Analysis and Applications of Monophasic Action...

Academic year 2010 - 2011

Analysis and Applications of

Monophasic Action Potentials in

Electrophysiology

Vincent KEEREMAN

Promotor: Prof. dr. ir. Patrick SegersCo-promotor: Prof. dr. Roland Stroobandt

Supervisors: Dr. Thierry Bove and Ir. Milad El Haddad

Thesis submitted in the 2nd Master as partialfulfillment of the requirements for

MASTER IN MEDICINE

The author and promotors give the authorization to consult and copyparts of this thesis for personal use. Any other use is subject to copyrightlaw, especially concerning the obligation to refer to the source whenever re-sults from this thesis are cited.

Date: 5/04/2011

Vincent Keereman Prof. dr. ir. Patrick Segers

Preface

Many people have been involved in the work presented in this thesis.First of all I would like to thank prof. dr. ir. Patrick Segers for takingon the promotorship of this master thesis and granting me the freedom tochoose my own direction in the research process. I also want to acknowledgethe help of prof. dr. Roland Stroobandt. I have learnt a lot about cardiacelectrophysiology during the many interesting discussions we have had inthe last two years. I want to thank dr. Thierry Bove for giving me theopportunity to collaborate on the subject that he is investigating for his PhD.I owe specific gratitude to him for holding the MAP electrode for so manyhours of experiments. I also much appreciated the help of Milad El Haddad.It was nice to have another engineer in the room during the experiments,definitely when the recording equipment was causing trouble. I also want tothank dr. Stefaan Bouchez, Mieke Olieslagers and all other people who hadsome part in the experiments for their help.

Apart from the people who have contributed to this work directly, thereare many others to whom I owe gratitude for the support during my stud-ies. First of all I want to thank my girlfriend Lynn for always being thereand bearing with me through these busy times. Secondly I want to thank myparents and the rest of my family. They have always supported my decisionto start studying medicine and their continuing interest in my work is per-haps the most important motivator for me. I want to thank my friends forthe many good times we spent together. I strongly believe that it is only abalanced combination of work and pleasure that keeps a man productive. Ialso want to mention my colleagues at the MEDISIP research group, whereI have been working for almost four years now.The friendly atmosphere inthe group makes it so much fun to work there. I will definitely regret that Ihave to quit next year, when I start my medical internships.

Vincent Keereman, May 2011

Contents

Abstract 1

Samenvatting 3

1 Introduction 6

1.1 The cardiac action potential . . . . . . . . . . . . . . . . . . . 61.2 Acquisition methods . . . . . . . . . . . . . . . . . . . . . . . 8

1.2.1 First measurements . . . . . . . . . . . . . . . . . . . 81.2.2 Suction method . . . . . . . . . . . . . . . . . . . . . . 91.2.3 Contact electrode method . . . . . . . . . . . . . . . . 111.2.4 Intramural measurement . . . . . . . . . . . . . . . . . 12

1.3 Origin of the signal . . . . . . . . . . . . . . . . . . . . . . . . 121.3.1 Measurement set-up and MAP morphology . . . . . . 131.3.2 1930 - 2004: changing opinions . . . . . . . . . . . . . 141.3.3 Unifying theory . . . . . . . . . . . . . . . . . . . . . . 17

1.4 Properties of monophasic action potentials . . . . . . . . . . . 201.4.1 Correlation with transmembrane action potentials . . 201.4.2 Field of view . . . . . . . . . . . . . . . . . . . . . . . 211.4.3 Afterdepolarizations . . . . . . . . . . . . . . . . . . . 221.4.4 MAP duration . . . . . . . . . . . . . . . . . . . . . . 23

2 Measurements 26

2.1 Experimental setup . . . . . . . . . . . . . . . . . . . . . . . . 262.2 MAP induction . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2.3 Artefacts in the MAP signal . . . . . . . . . . . . . . . . . . . 282.3.1 Stimulus artefact . . . . . . . . . . . . . . . . . . . . . 282.3.2 Wandering baseline . . . . . . . . . . . . . . . . . . . . 302.3.3 Negative terminal deflection . . . . . . . . . . . . . . . 302.3.4 Diastolic deflections . . . . . . . . . . . . . . . . . . . 36

3 Analysis 39

3.1 Manual analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 403.2 Algorithm overview . . . . . . . . . . . . . . . . . . . . . . . . 413.3 Artefact handling . . . . . . . . . . . . . . . . . . . . . . . . . 423.4 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . 443.5 Graphical User Interface (GUI) . . . . . . . . . . . . . . . . . 463.6 Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

4 Application 50

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

5 Conclusion 57

Bibliography 60

A Permission to use copyrighted material 64

Abstract

INTRODUCTION Tetralogy of Fallot (ToF) is a congenital heart de-fect which occurs in approximately 3 out of 10.000 live births. It is causedby pathological development of the right ventricular infundibular septumand results in 4 key anatomic features: overriding aorta, right ventricularoutflow tract (RVOT) obstruction, ventricular septum defect and hyper-trophy of the right ventricle. Surgical correction is usually successful byprimary repair, despite some residual dysfunction of the right ventricularoutflow tract. Most often a combination of scar tissue in the right ventricleand pulmonary valve incompetence is seen. The damaged pulmonary valveleads to chronic volume overload and dilatation of the right ventricle. Somepatients also develop late arrhythmias, eventually causing sudden death. Itis unclear whether these arrhythmias are caused by the dilatation of theright ventricle, by the scar tissue in the right ventricle, or by a combinationof both.

Monophasic action potentials (MAPs) can be used to investigate thelocal repolarization properties of cardiac tissue. In contrast to transmem-brane action potentials (TAPs), which are difficult to measure on a beatingheart, MAPs can be acquired in in-vivo studies. Therefore, this techniqueis useful for investigations of the electrophysiological properties of cardiactissue in pathological conditions. The analysis of MAPs has mostly beendone manually, as the recordings can be subject to many artefacts. Thesemake automatic analysis difficult.

METHODS In a first study, we investigated the origin of several arte-facts seen during MAP recordings. Based on the results of these investiga-tions an automatic processing algorithm was designed and implemented inMATLAB. The algorithm allows the determination of the action potentialduration (APD), which is a quantitative parameter related to the repolar-ization of the cardiac tissue. A graphical user interface was also designedto enable quick and correct analysis of multiple MAP recordings. The algo-rithm was validated against manual analysis of 24 MAPs for its reliability.

1

In a second part, the electrophysiological effects of the late sequelae ofsurgical repair of ToF were evaluated in a pig model. Three groups of 4animals, in whom a different surgical RVOT lesion was created, were com-pared to a sham group. The first group comprised 4 pigs with isolatedpulmonary valve insufficiency. Group 2 had an outflow patch inserted intothe infundibulum of the right ventricle, resulting in local scar tissue. Thethird group combined both the infundibular scar and pulmonary valve in-sufficiency. The control group had a normal right ventricular outflow tract.After 3 months, electrophysiological testing was done including the record-ing of MAPs from 4 different epicardial regions: the inflow part of the rightventricle (RVIT), the RVOT, the apex of the right ventricle (RVA) andthe apex of the left ventricle (LVA). The APD was determined using theimplemented algorithm.

RESULTS With corrections for the investigated MAP artefacts, theautomatic processing algorithm showed a close correlation with manual de-termination of the APD, with a statistically non-significant difference be-tween both analyses (p < 0.05). Based on the reliability of this method,the algorithm was used for examination of the APD in the animal study.A statistically significant (p < 0.001) shorter APD was found in group 2 inthe RVOT region and in group 3 in both the RVIT and RVOT region incomparison with the control group.

CONCLUSION The feasibility of performing automatic analysis ofMAP recordings was shown. Good reliability compared to manual analysiswas also demonstrated. The applicability of the algorithm has been shown ina larger study, investigating the electrophysiological effects of surgical repairof ToF on the right ventricle in an animal model. The first results indicatesignificant electrophysiological myocardial changes induced by scarring ofthe right ventricle. Isolated pulmonary valve insufficiency does not appearto affect APD significantly through proper right ventricle dilation. However,the first insights into these data are still preliminary and definite conclusionscan only be drawn at the endpoint of the complete project.

2

Samenvatting

INLEIDING Tetralogie van Fallot (ToF) is een congenitale hartaan-doening die voorkomt in ongeveer 3 op 10.000 levend geborenen. Het wordtveroorzaakt door een pathologische ontwikkeling van het infundibulair sep-tum van het rechter ventrikel en resulteert in 4 anatomische kenmerken:overrijdende aorta, obstructie van het uitvloeitraject van het rechter ven-trikel, ventrikel septum defect en hypertrofie van het rechter ventrikel. Chirur-gische correctie is meestal succesvol door primaire herstelling, ondanks watresiduele dysfunctie van het uitvloeitraject van het rechter ventrikel. Meestalwordt een combinatie van littekenweefsel in het rechter ventrikel en pul-monalisklep insufficientie gezien. De beschadigde pulmonalisklep veroorza-akt chronische volumeoverbelasting en dilatatie van het rechter ventrikel.Sommige patienten ontwikkelen ook cardiale ritmestoornissen op latere leeftijd,die uiteindelijk plotse cardiale dood veroorzaken. Het is onduidelijk of dezeritmestoornissen veroorzaakt worden door de dilatatie van het rechter ven-trikel, door het littekenweefsel, of door een combinatie van beide.

Monofasische actiepotentialen (MAPs) kunnen gebruikt worden op delokale repolarizatie-eigenschappen van hartweefsel te onderzoeken. In tegen-stelling tot transmembranaire actiepotentialen (TAP’s), die moeilijk meet-baar zijn op een kloppend hart, kunnen MAPs gemeten worden in in-vivo ex-perimenten. Deze techniek is daarom interessant om de elektrofysiologischeeigenschappen van cardiaal weefsel in pathologische omstandigheden te on-derzoeken. De analyse van MAPs wordt meestal manueel gedaan, aangeziende opnames vaak veel artefacten vertonen. Deze artefacten bemoeilijken deautomatische analyse.

METHODEN In een eerste deel onderzochten we de oorsprong vanverschillende artefacten die gezien werden tijdens MAP experimenten. Opbasis van de resultaten van dit onderzoek werd een automatisch verwerk-ingsalgoritme ontworpen en geımplementeerd in MATLAB. Het algoritmelaat de bepaling van de duurtijd van de actiepotentiaal (APD) toe. Dit iseen kwantitatieve parameter gerelateerd aan de repolarizatie van cardiaal

3

weefsel. Een grafische gebruikersinterface werd ook ontworpen om snelle encorrecte analyse van meerdere MAP opnames mogelijk te maken. Het algo-ritme werd gevalideerd tegenover de manuele analyse van 24 MAPs om debetrouwbaarheid te evalueren.

In het tweede deel werden de elektrofysiologische effecten van de sequelaevan chirurgische correctie van ToF bestudeerd in een varkensmodel. Driegroepen van 4 dieren, waarin een verschillende chirurgische lesie gecreerdwerd in het uitvloeitraject van het rechter ventrikel (RVOT), werden vergelekenmet een controlegroep. De eerste groep bestond uit 4 varkens met geısoleerdepulmonalisklep insufficientie. Groep 2 kreeg een uitvloei patch in het in-fundibulum van het rechter ventrikel met als resultaat lokaal littekenweefsel.De derde groep had zowel een infundibulair litteken als een pulmonalisklepinsufficientie. De controlegroep had een normaal RVOT. Na drie maan-den werd een elektrofysiologische evaluatie gedaan, inclusief de meting vanMAPs op 4 verschillende epicardiale regio’s: het invloeigedeelte van hetrechterventrikel (RVIT), het RVOT, de apex van het rechter ventrikel (RVA)en de apex van het linker ventrikel (LVA). De APD werd bepaald met hetgeımplementeerde algoritme.

RESULTATEN Het algoritme toonde een goede correlatie met manueleanalyse van de APD, met een statistisch niet-significant verschil tussen beideanalysen (p > 0.05). Omwille van de betrouwbaarheid van deze methodewerd ze gebruikt voor de analyse van de APD in een studie met een dier-model. Een statistisch significant (p < 0.001) kortere APD werd gevondenin groep 2 in het RVOT en in groep 3 in zowel het RVOT als het RVIT invergelijking met de controlegroep.

CONCLUSIE De haalbaarheid van automatische analyse van MAPsignalen werd gedemonstreerd. Een goede betrouwbaarheid in vergelijkingmet manuele analyse werd aangetoond. De toepasbaarheid van het algo-ritme werd geıllustreerd in een grotere studie, die de elektrofysiologischeeffecten van de chirurgische correctieprocedure voor ToF op het rechter ven-trikel onderzocht. De eerste resultaten tonen significante elektrofysiologis-che veranderingen geınduceerd door littekenweefsel in het rechter ventrikel.Geısoleerde pulmonalisklep insufficientie blijkt de APD niet significant te

4

beınvloeden door rechter ventrikeldilatatie. De eerste inzichten in dezedata zijn echter nog preliminair en definitieve conclusies zullen pas kunnengetrokken worden op het einde van het volledige project.

5

Chapter 1

Introduction

In this chapter the concept of monophasic action potentials is introduced.First we recapitulate the shape of a normal ventricular action potential.Then the different acquisition methods that can be used to acquire a monopha-sic action potential (MAP) are discussed. Since the start of MAP acquisi-tions, there has been a lot of debate on the origin of the signal. In thethird section we elaborate on the most important theories that have beenproposed. The last section covers some general properties of MAPs, whichare relevant to the rest of the thesis.

In the next chapter the acquisition of MAPs is discussed, together withthe problems that can occur during MAP experiments. The third chaptercovers the analysis of MAP signals. An automatic processing algorithmis also derived in the third chapter. In the fourth chapter the designedalgorithm is used to analyze MAP measurements acquired in a study inan animal model of Tetralogy of Fallot. Chapter 5 contains a summarizingconclusion.

1.1 The cardiac action potential

The cardiac action potential has a much longer duration than an actionpotential generated by a nerve cell because the contraction of the heart dur-ing systole lasts for several hundred milliseconds. The shape of the cardiac

6

CHAPTER 1. INTRODUCTION 7

Figure 1.1: The normal shape of a cardiac action potential with the ionfluxes causing it. Figure courtesy of R. Stroobandt.

action potential has been studied extensively, mainly by the measurementof transmembrane action potentials. This is done by measuring the voltagebetween a microelectrode that is plunged through the cell wall of a sin-gle cardiac cell and a reference electrode in the extracellular fluid. Usingthis setup the measured signal is strongly negative (-80 mV) or ”polarized”during diastole and becomes slightly positive (+ 20 mV) or ”depolarized”during systole.

The different phases in the cardiac action potential are governed by fluxesof different ions, going either inward or outward. Fig. 1.1 shows a schematicdrawing of a cardiac action potential and the ion fluxes that generate it.The first phase (phase 0) is the fast upstroke, which is caused by very rapidinflux of Na+ ions, which causes rapid depolarization of the transmembranevoltage. These Na+-channels become unexcitable (refractory) and closewhen the transmembrane voltage reaches a certain level. Phase 1 is a briefand incomplete repolarization caused by the closing of the Na+-channels. Inphase 2, called the plateau phase, the depolarization of the cell is maintainedby influx of Ca++ ions. Outflux of K+ ions causes the repolarization tothe resting potential (phase 3). Phase 4, which is the diastolic phase, ischaracterized by a constant resting potential.

As the cardiac action potential is the base of cardiac electrophysiology,it is interesting to investigate its changes in pathologic conditions. This canbe done in-vitro using transmembrane action potentials. However, it wouldbe interesting if it would also be possible to investigate the cardiac action


potential in-vivo on the beating heart. Transmembrane action potentials canbe acquired on a beating heart, but this is very difficult and impractical.In the rest of this thesis the concept of monophasic action potentials isdiscussed. This is a measurement technique which enables the acquisition ofcardiac action potentials in-vivo. In the last part of this work, the conceptof MAPs is extended to the measurement and analysis of multiple in-vivocardiac MAPs.

1.2 Acquisition methods

1.2.1 First measurements

The first acquisition of a MAP was performed in 1888 by Burdon-Sandersonand Page[1]. They investigated the time-relations in the activation of theventricle of the frog heart. They measured the epicardial electrocardiogram(ECG) by means of a much more complicated setup than we know of nowa-days, as Einthoven had yet to invent his string galvanometer and apply itto ECG. Measurements of the conduction velocity and effective refractoryperiod (ERP) were done. They acquired the first MAP while investigat-ing the effect of injury on the epicardial ECG. By producing a burn injuryon the epicardial surface and measuring the voltage difference between thisinjured spot and a non-injured spot, they saw that ”[...] if either of theleading-off contacts is injured the terminal phase disappears, and the initialphase is followed by an electrical condition in which the injured surface ismore positive [...] relatively to the uninjured surface”. This also shows theorigin of the term ”monophasic”: up to that moment, all acquired electro-cardiograms were multiphasic, as they were acquired using bipolar leads.The injury potential that was measured showed only one phase: a positiveone, which lasted for the entire contraction of the ventricle. A graph repre-senting the voltages they measured is shown in fig. 1.2. The shape of themeasured injury potential resembles that of a MAP, as will be seen later.


Figure 1.2: The measurement of Burdon-Sanderson and Page: a biphasic(from an uninjured region) and monophasic (from an injured region) actionpotential.

1.2.2 Suction method

Creating a frank injury, such as burning the epicardium or stabbing a holeinto the epicardium, was obviously not a good method for research. Usingthis method, questions would remain whether the measured signal was notpurely related to the injury that was created, and had no relevance to viablecardiac tissue. It was Schutz who introduced the suction method in 1934 andthereby provided a more useful technique for acquiring monophasic actionpotentials[2]. His method consisted of sucking up a piece of epicardial tissueinto a tube by use of a vacuum pump, tying off this piece of tissue andthen applying an electrode to the tied off tissue, while a reference electrodewas placed on viable tissue. Wiggers improved this method in 1936 byusing a tube which had an electrode inside, thereby making the tying offunnecessary[3]. This configuration is illustrated in fig. 1.3. An improvedsuction electrode design was presented by Churney et al. in 1964[4]. Theyalso evaluated the difference between MAPs acquired with suction electrodesand MAPs acquired with stab electrodes. They showed that, although the


Amplifier

‐+

Suc/ontube

Cardiac/ssue

Depolarizedregion

Figure 1.3: The suction method.

form of MAPs was comparable, MAPs acquired with the suction methodhad a higher amplitude and proved more stable over time.

All of the previous measurements were only performed on animals andon the epicardium. The first measurements of endocardial MAPs in-vivowere done in Lund, Sweden in 1966. A new suction electrode was designedby Sjostrand and tested on dogs[5]. Korsgren did the first measurementsin man[6], showing MAPs of the right atrium in 3 patients during diagnos-tic catheterization. The first study showing that useful clinical informationcould be retrieved from MAP measurements was done by Shabetai et al. in1968[7]. They evaluated the effect of infusion with CaCl, EDTA and acetyl-strophantidin on the shape and duration of the MAP in the right atrium andright and left ventricle. They showed that the effect was comparable to thatseen in epicardial measurements in dogs. These measurements showed thepossibility of using MAPs for the evaluation of the effect of drugs on the car-diac action potential in-vivo. During the following years, the suction methodwas further improved by Olsson[8]. He also discussed the precautions thatshould be taken in order to ensure safe application of this method. Forexample, extra filters had to be used in order to prevent air emboli. Theseconcerns led to the fact that the suction method was never widely used in a


clinical setting - it was also never FDA approved.

1.2.3 Contact electrode method

Injury or suction of epicardial tissue generates a map by depolarizing theaffected part of the epicardium. Applying light to moderate pressure tothe epicardium can have the same effect. This was first shown in-vivo byJochim in 1934[9]. He was working in the group of Katz, who were atthat time looking for the origin of the T-wave[10, 11]. He acquired MAPsfrom the epicardial surface of dog hearts by applying light to moderatepressure on a glass electrode, leading to a minor and reversible injury. Healso showed that, in order for the MAP to be positive, the electrode on theinjured region should be connected to the positive terminal of the amplifier.As will be discussed in the next section, there was already debate at thattime which electrode was the ”different” electrode. Jochim was convincedby basic measurements that it was the electrode on the uninjured regionthat was providing the signal.

Although the contact electrode method had the advantage of inflicting noreal injury (with the suction method this could still be debated), it was quitehard to implement for clinical use as well. While there were no concernsfor safety with this method, there were problems with obtaining a stableMAP signal. The suction electrode is tightly fastened to the endocardialwall and is not affected by motion of the heart. The contact electrode isnot attached to the endocardial wall and this leads to bad signal qualityin some cases. It was only in 1980 that Franz and colleagues developeda new contact electrode and showed clinical applicability for measurementof atrial MAPs (fig. 1.4)[12]. In the following years they demonstratedthe possibility of acquiring stable MAP signals in the atria and ventriclesfor over one hour[13]. An improved electrode was presented by the samegroup in 1991[14], where pacing electrodes were also mounted onto the MAPelectrode. This provided the possibility of pacing and measuring a MAP atthe same location. Since 1980, the contact electrode method was the mostwidely used and has gained clinical acceptance as well as FDA approval.


Amplifier

‐+

Pressure

Cardiac3ssue

Depolarizedregion

Figure 1.4: The contact electrode method.

1.2.4 Intramural measurement

Yet another design for MAP measurements was presented by Nesterenkoin 1995[15]. It consists of one electrode which is placed on a small regiondepolarized using KCl and another electrode which consists of a thin tung-sten wire inserted into viable uninjured cardiac tissue (fig. 1.5). Althoughthis method is not applicable to endocardial clinical measurements, it hasa smaller field of view than the contact electrode method and can thereforebe interesting for use in epicardial research measurements.

1.3 Origin of the signal

From the start of experiments with MAPs there has always been the ques-tion which electrode was the different electrode. Multiple researchers haveintensively debated whether the MAP signal characteristics are generatedby the electric activity of the injured (by pressure, suction, ...) or the un-injured (reference) region. In this section we will first describe the normalconfiguration that is used to measure a MAP and the morphology of a nor-mal MAP. Then we will briefly discuss the different opinions that have beenargued since the 1930’s. After that a theory is introduced which explains


Amplifier

‐+

KCl

Cardiac1ssue

Depolarizedregion

Figure 1.5: The intramural method.

all the observations that have been made concerning the origin of the MAPsignal.

1.3.1 Measurement set-up and MAP morphology

To understand the discussion explained below, the reader needs a conceptualunderstanding of how a MAP is measured. As explained in the previous sec-tion, a MAP is a voltage signal measured between an injured region of theheart and an uninjured region of the heart. It is therefore a bipolar signal(both electrodes are placed on the heart). In general, the electrode on theinjured surface is connected to the positive terminal of the amplifier. Thisyields a negative signal during rest and a positive signal during excitationof the cardiac cells, as shown in fig. 1.6. As the measured voltage is the po-tential difference between both electrode sites, this means that the potentialof the injured region is smaller than the potential of the uninjured regionduring rest, and vice versa during excitation. The question at hand is nowwhat causes the positive MAP signal during excitation: is it the potential ofthe injured region becoming larger or is the potential of the uninjured regionbecoming smaller? This is important with respect to the interpretation ofthe MAP signal. Indeed, in the first case this means that MAPs reflect the


‐20mV

0mV

+50mV

REST ACTIVATION

Figure 1.6: Shape of a normal MAP measurement.

properties of the injured tissue or its surroundings. In the latter case a MAPreflects the properties of the healthy tissue.

1.3.2 1930 - 2004: changing opinions

At first it was considered logical that only the uninjured region could con-tribute to the genesis of the MAP signal, as the injured region was assumedto be electrically inactive. Wilson[16] was the first to show that this is afalse assumption. He showed with measurements on tortoise hearts that thevoltage measured with a unipolar electrode on the injured region changedduring the excitation cycle. He was therefore convinced that, as MAPs couldonly be measured if an electrode was placed on an injured region, the injuredregion was generating the signal. Jochim did not agree with this opinion. Inhis paper describing the first MAP measurements with the contact electrodemethod, he also did some measurements to determine which electrode wasthe different one[9]. He saw that changes to the injured region, such as achange in electrolyte content, did not affect the MAP. If the same changeswere made in the uninjured region, the MAP was changed. He thereforeconcluded that it was the uninjured region that formed the MAP signal.

Eyster, working in the same group as Jochim, did further measurementsand calculations to determine the origin of the MAP signal. In 1938 heclaimed to have found the explanation[17]. Rather than trying to determinethe origin of the signal by changing the properties of the tissues measured, hetried to measure the potential distribution in the injured region. He observed


that, during activation, the potential change in the injured region was muchlarger than in the uninjured region. In fact, the large potential in the injuredregion almost completely obliterates the signal from the uninjured region.This was demonstrated for example when he put the injured region on theatrium and the uninjured region on the ventricle[18]. The general shapeand amplitude of the MAP stayed the same, but a small deflection in theatrial MAP was seen at the moment of ventricular activation. From hisexperiments, he concluded that the MAP signal was for the largest partgenerated by the injured region and the healthy cells directly surroundingthis region.

Eyster also searched for the physical explanation behind the signal thatwas measured. He argued that the observed potential change could only becaused by a charge distribution with two rings at the border of the injuryregion. This is depicted in fig. 1.7. During the resting state the inner ring isnegative and the outer ring is positive. This gives rise to the negative restingMAP, as the injured region will have a strongly negative potential. Whenthe surrounding tissue becomes active, the charge distribution is inverted,with the inner ring now being positive and the outer ring being negative.This yields a positive MAP during activation.

The most relevant part of Eyster’s theory was that the MAP signal wascaused by the tissue closely surrounding the region of injury. This wasfurther investigated by Franz[19, 14], working intensively with the contactelectrode method. He stated that the MAP was a reflection of the transmem-brane voltage of the cells in the margin around the injury. The measuredsignal is actually caused by current flow, the direction of which changes be-tween rest and activation. During rest, the current flows towards the injuryand yields a negative voltage. When the margin cells become active, theirmembrane voltage inverses and causes opposite current flow, yielding a pos-itive voltage. Franz also thought that the MAP signal was in part causedby the volume of uninjured cardiac muscle below the contact site which wasnot depolarized by pressure. This theory was interesting for the contactelectrode method, as it claimed that the field of view of this method waslimited to a few millimeters outside the contact electrode. The position of


Uninjuredregion

Depolarizedregion

‐

‐

‐

‐

‐

‐

‐

‐

+

+

+

+

+ +

+

+

Uninjuredregion

Depolarizedregion

+

+

+

+

+

+

+

+

‐

‐

‐

‐

‐ ‐

‐

‐

REST ACTIVATION

‐ + ‐ +

Figure 1.7: Eyster’s theory on the generation of the MAP signal: two con-centric charge rings.

the reference electrode, which is in general further away (≥ 5 mm), does notmake a big difference in this case. This makes the application of the contactelectrode method in a clinical setting, where it is often difficult to know theorientation of the catheter and the position of the reference electrode, mucheasier.

The theory of Franz was accepted for many years, until Kondo and col-leagues more recently raised questions about it[20]. They had developed anew method for measuring intramural MAPs, using KCl to create a depolar-ized region[15], as described in the previous section. Again they showed thatit was the uninjured region that was generating the signal. They measuredtransmembrane action potentials (TAPs), contact MAPs using a Franz-likecatheter and intramural MAPs using their own method. In a compara-ble experiment to the one performed by Jochim in 1938, they changed theproperties of the injured and uninjured regions by cooling and by injectingATX-II, a Na+-channel blocking agent. Only modifications in the uninjuredregion changed the MAP morphology. With this experimental setup theyalso showed that Franz’s claim that uninjured cells below the injured regioncontributed to the MAP signal was not true. This also shedded doubt on


the accuracy of measurements with the contact electrode method, definitelyconcerning the field of view of this method. A heavy debate followed betweenboth groups[21, 22], until Vigmond finely pointed out that they neither ofthem was completely right or completely wrong. He had already solved theproblem in 1999[23], but unfortunately his publication had gone unnoticeduntil then.

1.3.3 Unifying theory

Vigmond tackled the problem of the genesis of the MAP signal by usingcomputer simulations of the electromagnetic interactions that occur when aMAP is measured[24]. Although his theory was developed with the contactelectrode method in mind, it can be applied to all methods that measurethe signal between a depolarized (injured) region of cardiac tissue and areference region. His hypothesis is explained below. The symbols used arelisted in table 1.1 and also illustrated in fig. 1.8.

Table 1.1: Symbols used in the explanation of Vigmond’s hypothesis.Symbol Definition

VMAP Measured MAP voltage

V d Transmembrane voltage in the depolarized region

φdi Intracellular potential in the depolarized region

φde Extracellular potential in the depolarized region

V r Transmembrane voltage in the reference region

φri Intracellular potential in the reference region

φre Extracellular potential in the reference region

Two assumptions are needed for his theory to apply:

• The transmembrane voltage in the depolarized region (V d) is constant.

• The intracellular domain is well connected between the region underthe electrode (the depolarized region) and the reference region: φd

i =φr

i .


Figure 1.8: Illustration of the symbols used in Vigmond’s theory.

Using the definition of the transmembrane voltage:

V = φi − φe (1.1)

and as the measured MAP voltage is the difference between the extra-cellular potential below the electrode and at the uninjured region:

VMAP = φde − φr

e (1.2)

this means that the measured MAP voltage is actually the differencebetween the transmembrane voltages of the depolarized cells and the cellsin the reference region:

V r − V d = (φri − φr

e)− (φdi − φd

e) (1.3)

= φde − φr

e (1.4)

= VMAP (1.5)

As the transmembrane voltage in the depolarized region is consideredconstant, or at least only varies slightly with time, the MAP shape will thusbe a reflection of the transmembrane voltage of the reference region. Theabsolute value of the MAP voltage depends on the transmembrane voltageof both regions. Suppose for example that the transmembrane voltage ofthe depolarized region is fixed to -50 mV and that the reference regionis a volume of uninjured cells. As the resting transmembrane voltage of


uninjured cells is -80 mV, this will lead to a negative resting MAP of -30 mV. When the uninjured cells region produce an action potential, theirmembrane depolarizes up to a transmembrane voltage of +10 mV. Thiswould lead to a positive MAP amplitude of +60 mV.

With this theory the question about the genesis of the MAP signal reallybecomes the question of the field of view of the reference electrode. In thisrespect the experiments and conclusions of Kondo et al. seem correct. Ifit is accepted that the electrode they use as a reference electrode, a smalltungsten wire, has a small field of view, then it is clear that in their case theMAP signal will be a reflection of the transmembrane voltage of the cells ina small region. On a Franz catheter the reference electrode is located on theshaft of the catheter and about 5 mm away from the tissue surface. In thatcase it is much less clear what the field of view of the reference electrode isand hence which cells influence the measured MAP. It is conceivable thatlocal heterogeneities in transmembrane voltage will produce a MAP that isan average of the transmembrane voltage of the surrounding cells. This canproduce misleading results, as is discussed more in depth in the paragraphabout afterdepolarizations in the next section.

Some questions can still be raised with regards to the theory of Vig-mond. One of them concerns the amplitude of the MAP, which is smallerthan that of a transmembrane action potential. This can be explained byassuming that there are leakage currents in the membrane of the depolar-ized cells, leading to the fact that the transmembrane voltage of these cellsis not perfectly constant but changes in the direction of the transmembranevoltage of the reference cells. This will lead to a smaller MAP. If we assumethat the leakage current is inversely proportional to the stability of the de-polarization that is caused by the injury, this can also explain why differentMAP techniques lead to different MAP amplitudes. The suction method,which yields the most stable depolarization, also gives the largest and moststable MAPs. The quality of the MAPs generated by the contact electrodemethod largely depend on the quality of the contact that is made. If thepressure is varied, the MAP amplitude also varies. In all MAP methods theamplitude of the MAP falls after a period of time. This can be explained


by an increase in leakage current over time.

1.4 Properties of monophasic action potentials

1.4.1 Correlation with transmembrane action potentials

Although there was discussion about the origin of the MAP signal for along time, it was quickly seen that the shape and timing of the MAP signalresembled those of transmembrane action potentials (TAPs). Validationwas therefore sought to prove that MAPs could be used as an easier to usein-vivo alternative to TAPs. The first measurements of TAPs on beatingdog hearts were done in 1950 by Woodbury et al. and in 1951 by Draper etal[25, 26]. The first validation of MAPs against TAPs was done by Hoffmanin 1959 and was purely qualitative[27]. He performed measurements onisolated papillary muscles and perfused rabbit hearts. His most importantconclusions, which are still valid, were:

• The amplitude of a MAP is smaller than of a TAP and depends onthe type of injury. The largest amplitude is obtained using the suctionmethod.

• The depolarization phase is not representative for the TAP. This iscaused by dispersion: a MAP electrode is too large to measure indi-vidual cells, therefore the depolarization phase is an average of thedepolarization phases of a number of cells. This yields a slope that isless steep.

• The repolarization phase is comparable to the TAP.

• ”Bumps” and afterdepolarizations can sometimes be seen in MAPs,but they are most likely the effect of movement of the electrode.

In 1986 Franz did a quantitative in-vitro validation of a new MAPelectrode[28]. He investigated the duration at 30, 60 and 90 % repolar-ization of MAPs and TAPs in the isolated rabbit septum. Experiments


Figure 1.9: An overlap of a MAP and TAP signal measured by Franz etal. for the validation of their contact electrode method. Reproduced withpermission from [28].

were performed in different situations: during normal contractions, duringextrasystoles and during changed electrolyte balance (hypocalcemia and hy-perkalemia). He showed that the duration of MAPs and TAPs was similar(mean absolute difference ≤ 5 ms) and correlated (R ≥ 0.8). An illustrationof the excellent agreement of MAP and TAP measurements is shown in fig.1.9. In a comparable experiment Ino repeated these measurements in dogsin 1988[29].

1.4.2 Field of view

The field of view of the MAP electrode is important as this determines howaccurately MAPs can measure local repolarization changes. Levine triedto give a quantitative estimate of the field of view of MAP measurementsof isolated and superfused canine cardiac tissue[30]. In his experimentshe showed that the upstroke of the MAP contained information about thelocal conduction properties of the cardiac tissue. These properties thendetermine the field of view of the MAP. As local conduction depends onfiber orientation inside the cardiac tissue, this meant that the field of viewof the MAP can be different in different directions and therefore does not


need to be circular. Influences of cardiac tissue up to 10 mm away from thecontact electrode were seen in the MAP. However, as it is unclear from hispaper where the reference electrode was located, this particular distance isnot relevant considering the hypothesis of Vigmond.

Two years earlier, Franz et al. determined the border of myocardialischemia in-vivo in dogs after coronary artery occlusion which lead to asharply defined region of ischemia[31]. They showed that MAPs were moreaccurate than bipolar TQ-ST segment mapping. The resolution of the MAPmethod was estimated at around 5 mm, as this was the area over which theMAP changed from the healthy to the ischemic region. In a later paper,Franz claimed that the field of view could even be limited to the surfaceof the contact electrode[14]. This was not true, as Kondo showed in hispaper that a Franz-like catheter picks up signals from cells up to 5 mmaway from the contact electrode[20]. The intramural electrode had a muchsmaller field of view (≤ 1 mm). The reference electrode on the contactcatheter that was used by Kondo was 5 mm away. For mouse heart studies,Franz et al. have developed miniaturized versions of their catheter witha smaller contact electrode and a reference electrode that is closer to thecontact electrode[32]. It is conceivable that the field of view of this cathetermight be smaller, but it has never been quantitatively evaluated.

1.4.3 Afterdepolarizations

Early (EAD) or delayed (DAD) afterdepolarizations of the cardiac actionpotential can be measured with TAPs. These afterdepolarizations are im-portant, as they can cause arrhythmias. It would be very interesting ifEAD’s or DAD’s could also be reliably observed in the MAP signal. Thiswould enable the in-vivo determination of the proarrhythmic potential ofdrugs. However, as the MAP signal can be unstable and show artefactsresembling afterdepolarizations, the observation of afterdepolarization-likesignals in MAP recordings has always been handled with caution. Franz hasproposed a number of conditions under which an afterdepolarization seenon a MAP recording can be accepted as a true afterdepolarization[19]:


1. The baseline recordings (before the application of the drug) should bestable and show a good quality MAP. In particular, phase 3 should besmooth and phase 4 should be constant.

2. The afterdepolarizations obtained in-vivo should be compared to thoseobtained with TAP measurements with the same drug in-vitro.

3. After washout of the drug the recordings should be identical to thebaseline recordings.

Even then, there is no absolute proof that an afterdepolarization-likesignal in the MAP is a real afterdepolarization. In fact, Kondo showed inhis paper in 2004 that the apparent afterdepolarizations in the MAP signalacquired with a Franz-like catheter can be pure artefacts[20]. Suppose thattwo types of cells with different repolarization time courses (one shorter thanthe other) are within the field of view of the reference electrode. Using thetheory explained above, both types of cells will contribute to the measuredMAP signal and this MAP will be an average of the transmembrane voltagesof both types of cells, as shown in fig. 1.10. It can easily be observed thatthis will lead to an apparent afterdepolarization in the MAP signal. Whenusing the intramural MAP electrode design used by Kondo, it could bepossible to register true afterdepolarizations.

1.4.4 MAP duration

Definition

When MAPs are used for analyzing the repolarization time course of cardiactissue, a quantitative parameter is needed to measure this. In this purposethe MAP duration is used. The start of the MAP can easily be defined asthe start or the steepest part of the upstroke. However, as the repolariza-tion ends asymptotically, the end of the MAP is more difficult to define.Some authors have suggested defining the end of the MAP as the intersec-tion between the diastolic baseline and a tangent placed on phase 3 of theaction potential[33]. This can lead to arbitrary results, as the placement


+

Figure 1.10: The composition of TAP signals from regions with differentrepolarization courses can lead to an apparent afterdepolarization in therecorded MAP signal.

of the tangent on the repolarization phase can be arbitrary. We prefer thedefinition of Franz, where the action potential duration can be measured atdifferent percentages of repolarization[13]. The amplitude is then definedas the difference between the crest of the MAP plateau and the diastolicbaseline. The action potential duration (APD) at e.g. 30, 60 and 90 %repolarization can then be measured as shown in fig 1.9.

Automatic analysis

During an electrophysiologic study, thousands of MAPs can be recorded.Analysis of MAPs has in general been done manually, due to the difficultnature of the signal. However, some automatic implementations have beenproposed. The group of Franz developed a method for automatic analy-sis of the APD at user-defined levels of repolarization[34]. They validatedtheir program against two observers who did manual determination of theAPD. The inter-observer variation was larger than the observer-computervariation. The computer was obviously much faster than the observers: 1minute versus 2-4 hours. A comparable program was developed by Yuan etal. and validated with one observer[35]. In both implementations, manualvalidation of the APD analysis is still needed in order to exclude MAPs that


were not correctly measured.

Chapter 2

Monophasic action potential

measurements

The goal of this chapter is to provide insight into the acquisition of MAPsand the problems that can be encountered. First the setup of an acquisitionsystem for MAP measurements is discussed. Then the induction of a MAPsignal from the epicardium of a pig heart is illustrated. The largest part ofthis chapter is dedicated to a description of the artefacts in MAP signals.The underlying cause of each artefact is investigated, as this is importantfor the analysis of MAP signals.

2.1 Experimental setup

All measurements were done in the laboratory for experimental surgery atGhent University Hospital. The presented signals were acquired from theepicardium of female pigs during open-chest surgery. The EPTracer system(CardioTek, Maastricht, The Netherlands) was used for recording signals.This system provides the possibility to visualize and record up to 20 bipolaror unipolar signals simultaneously. Standard surface limb leads and up to3 pressure channels can be recorded at the same time. Basic filters, suchas a notch filter to remove A/C noise from the signals, are available to theuser. Apart from recording signals 2 stimulation channels can also be used

26

CHAPTER 2. MEASUREMENTS 27

to stimulate the heart.The MAPs were measured from the epicardial surface using a HSE-

Harvard MAP catheter (Hugo Sachs Elektronik, March-Hugstetten, Ger-many). The MAP catheter is of the contact electrode type, with a tipelectrode that is used to apply pressure. The catheter is pressed againstthe epicardium manually to depolarize the underlying tissue. A referenceelectrode is mounted on the shaft of the catheter, about 5 mm proximalfrom the tip electrode. The tip electrode is connected to the positive in-put and the reference electrode to the negative input of one of the channelsof the EPTracer system. The MAP is recorded as a bipolar signal with ahigh pass filter (cutoff frequency 0.05 Hz). Pacing was done using a simplebipolar electrode that was attached to the epicardium of the apex of the leftventricle. The leads of the pacing electrode were also connected to one ofthe channels of the EPTracer system.

2.2 MAP induction

As has already been elaborately discussed above, a MAP signal can onlybe measured if the tissue below the electrode connected to the positive in-put (the tip electrode in our case) is depolarized. This means that a MAPdoes not appear from the moment the electrode contacts the epicardium.Instead, it is generated over a few beats. This can be seen in fig. 2.1. Thecatheter first touches the epicardium around 2 seconds from the start ofthe displayed recording. Stable contact is made with the epicardium at 4seconds. A multiphasic bipolar epicardial ECG is then measured for threebeats. This consists of a short QRS-complex followed by a constant STsegment and finishes with a wider negative T-wave. In the next two beats- starting at approximately 6.5 seconds - the tissue under the tip electrodegets more and more depolarized and starts acting as a reference. This depo-larization leads to a change in waveform, from multiphasic to monophasic.The QRS-complex is now converted to the MAP upstroke, the T-wave isconverted to the MAP repolarization phase. This measurement shows howa MAP can only be measured if the underlying tissue is sufficiently depolar-


Figure 2.1: Induction of a monophasic action potential. The buildup of themonophasic action potential takes place over several heartbeats.

ized. A non-perfect MAP is generated, with some artefacts in the diastolicinterval (the baseline is not flat). However, as will be shown below, thisMAP is certainly of high enough quality to allow automatic analysis.

2.3 Artefacts in the MAP signal

MAP signals can show a lot of artefacts. To enable the analysis of MAPsignals the origin of these artefacts should be investigated. From that infor-mation the proper way of handling these artefacts can be deducted. In thissection four different artefacts are discussed that are frequently observedin MAP signals. For each artefact an example is given and the supposedunderlying cause is investigated. The next chapter covers the handling ofthese artefacts in automatic analysis.

2.3.1 Stimulus artefact

As the duration of the cardiac action potential is strongly dependent on thepreceding diastolic interval, most MAP measurements are done while theheart is paced at a certain cycle length. In our experiments bipolar epicar-dial pacing was performed from the left ventricular apex. The stimuli that


Figure 2.2: A MAP measurement in sinus rhythm (top) and while pacingat a cycle length of 400 ms (bottom), illustrating the stimulus artefact.

are applied by this electrode generate a deflection on the MAP signal. Anexample of a MAP measurement during sinus rhythm and during pacing isshown in fig. 2.2. This stimulus artefact can be seen as a far field mea-surement. It is not caused by cardiac muscle contractions or even actionpotentials in the cells close to the pacing electrode. The stimulus artefactcan be distinguished from a MAP signal as it is much shorter in duration,has a multiphasic appearance and mostly has a smaller amplitude than theMAP.


Figure 2.3: Strong baseline wander in a MAP measurements where thereference electrode was not well-submersed into the blood pool.

2.3.2 Wandering baseline

It is often difficult to acquire a MAP signal with a stable baseline over along period of time. Sometimes it is even difficult to record a signal that hasa stable baseline over a short period of time, e.g. 10 seconds. The variationof the baseline over periods of seconds is called wandering baseline. It is anartefact that also may occur during the recording of ECG’s and is mostlydue to cable movements or bad electrode contact.The wandering baselineseen in MAP measurements probably has a comparable cause. The MAPmeasurement shown in fig. 2.3 was acquired with the reference electrode notsubmersed in the blood pool (usually it is submersed). It shows strong base-line wander, which is related to bad contact between the reference electrodeand the blood pool.

2.3.3 Negative terminal deflection

A high-quality MAP measurement is purely monophasic and therefore onlyshows a positive phase. However, in many measurements we observed anegative deflection at the end of the MAP wave. An example is shown infig. 2.4. This negative deflection is not seen in TAP measurements and istherefore an artefact. The origin of this artefact was unclear at the startof our experiments. Franz et al. claim that this artefact is caused by the


Figure 2.4: An example of a MAP measurement with a clear negative de-flection.

change in depolarization of the cells under the tip electrode. This changein depolarization could be caused - although never proved - by a drop inpressure on the tip (when measuring on the endocardium) at the beginningof diastole as the heart wall starts moving outwards.

The origin of the artefact is important in order to know the meaningof a MAP with a negative terminal deflection. Indeed, if the APD at X %repolarization has to be calculated, the level of 100 % repolarization needsto be clear. Is it at the minimum? Or is it at the intersection with thediastolic baseline just before the MAP? We therefore decided to investigatethis artefact thoroughly. In our opinion there are three possible causes forthe artefact: pressure, blood contact or far field.

Pressure

At the start of diastole, the heart moves towards the tip electrode in epi-cardial measurements. Therefore the pressure on the tip electrode couldincrease. If we assume that the depolarization increases ( = the transmem-brane voltage of the cells under the tip electrode becomes less negative) withincreasing pressure, this could cause the negative deflection. Indeed, if we


Figure 2.5: MAP measurements with low (top) and high (bottom) pressureon the MAP tip.

look at the formula from Vigmond’s theory:

VMAP = V r − V d (2.1)

an increase in V d will lead to a more negative MAP. If this is causing thenegative deflection, a difference in this artefact should be seen when applyingmore or less pressure to the catheter. Fig. 2.5 shows two MAP measurementsdone with high and low pressure on the electrode. The measurements weredone at the same location on the heart with only a few seconds in between.It is clear that the low-pressure measurement has a lower quality and shows amuch less stable signal. However, there is no apparent change in the shape oramplitude of the negative terminal deflection between both measurements.It is therefore unlikely that the artefact is caused by pressure. Anotherargument against this theory is that the same artefact can be observedin epicardial and endocardial measurements, while the pressure change isopposite in both situations.


Blood contact

In epicardial measurements during open-heart surgery there is usually enoughblood in the pericardial sac so that the tip electrode as well as the referenceelectrode are submersed in blood. However, the blood is removed by suctionfrom time to time. This leads to less blood in the pericardial sac, and thereference electrode may then only be submersed in blood during systole.The change in contact between the reference electrode and the blood couldalso cause the negative terminal deflection, as it is then unclear what thereference electrode is measuring.

Fig. 2.6 shows two MAP measurements, one with the reference electrodesubmersed in the blood pool and one where this was not the case. Themeasurement with no contact between the blood and the reference electrodeis of lower quality, showing a less steep upstroke and a varying baseline.However, the negative terminal deflection is present in both measurements.Therefore we can conclude that the negative terminal deflection is not causedby a lack of contact between the reference electrode and the blood pool.

Far field

The negative terminal deflection could also be explained as far field ”pol-lution” in the signal measured on the reference electrode. Indeed, if thereference electrode measures a wide field-of-view, which is conceivable inepicardial measurements with the contact electrode method, the repolar-ization of all cells in the heart could contribute to the MAP signal. Therepolarization of the heart can be seen on the ECG as the T-wave. Weobserved that the negative terminal deflection was mostly seen during theT-wave on the surface ECG.

A special measurement was set up to verify if this could explain the arte-fact. The signals from both electrodes on the MAP catheter were acquiredas two unipolar signals instead of a combined bipolar signal. The resultsare depicted in fig. 2.7. The unipolar signals were too large to acquire withthe amplifier so unfortunately the signals are saturated. However, the mostimportant observations can still be made:


Figure 2.6: MAP measurements with the MAP electrode submersed in theblood pool (top) and not submersed in the blood pool (bottom).

1. The tip electrode measures almost a block wave, which has a highamplitude.

2. The shape of the MAP originates from the reference electrode. Thesignal is upside down, as the reference electrode is connected to thepositive terminal of the channel in the unipolar measurement, whereasit is usually connected to the negative terminal for the bipolar MAPmeasurement.

3. The terminal deflection is measured by the reference electrode, not thetip electrode. This is more proof that pressure can not be the causeof the artefact.

4. The terminal deflection is coincident with the T-wave on the surfaceECG. There is also a small deflection just before the MAP upstroke,this is seen in conjunction with the QRS-complex of the ECG.

5. The third beat, which is an extra beat, has a larger QRS-complex and


Figure 2.7: The origin of the negative terminal deflection. Top: unipolarmeasurement from the MAP tip electrode (saturated). Middle: unipolarmeasurement from the MAP reference electrode (saturated). Bottom: aVRlead of the surface ECG. All measurements were done simultaneously.


a larger T-wave in the ECG. This beat also shows a distinctly largerterminal deflection.

Therefore, it is likely that the negative terminal deflection in the MAPoriginates from the T-wave of the far field that is measured by the referenceelectrode. Another argument in favor is that the negative deflection wasoften more pronounced in MAP measurements on the epicardium of the leftventricle. The left ventricle has the largest muscle mass and will thereforealso give rise to the largest part of the T-wave. If the negative terminaldeflection is caused by the far field, this will lead to a larger deflection inMAP measurements on the left ventricle.

Interpretation

It can be questioned now how MAPs with a negative terminal deflectionshould be analyzed? What is the signal level at which the MAP is com-pletely repolarized? Under the assumption that the T-wave causes the neg-ative terminal deflection, it is clear that the baseline that is seen before theupstroke should be used as the reference level. Indeed, the T-wave will causea negative superposition onto the original monophasic signal, but this farfield signal will eventually return to 0, just like the surface ECG in diastole.Just before the MAP it has definitely returned to 0, as the heart is com-pletely repolarized. Therefore the effect of the far field at that moment isminimal. This means that this level can be used as a reference.

2.3.4 Diastolic deflections

The diastolic baseline of a MAP measurement should be constant. Apartfrom the problem of wandering baseline, which is discussed above and evolvesfrom beat to beat, there are also small deflections during diastole that canbe observed in some measurements. These could be delayed afterdepolar-izations, but this seems unlikely as it is often seen in a measurement wherethese afterdepolarizations are not expected. The deflections can also disap-pear and reappear in an apparently random manner. Therefore it is likelythat these deflections are also artefacts.


As the amplitude of the deflections is small and no other explanationcould be found, we proposed that these deflections could be caused by move-ment of the catheter, or pressure changes on the tip electrode. To get aqualitative impression of the pressure changes on the tip electrode, a Swan-Ganz catheter (normally used for measuring pulmonary artery pressure) waspressed against the epicardium close to the MAP electrode. The pressurechanges in the Swan-Ganz catheter were recorded on a pressure channel ofthe EPTracer system, simultaneously with the MAP signal. The results ofthis experiment are shown in fig. 2.8.

At the moment of the small diastolic deflections, there is a sharper de-flection in the contact pressure curve. During the rest of the MAP cycle nosharp abrupt changes in the contact pressure curve can be observed. Thismeasurement provides some indication that the diastolic deflections couldbe related to pressure changes. It also provides more proof that the nega-tive terminal deflection discussed above is definitely not caused by pressurechanges, as there is no change in pressure during that artefact.


Figure 2.8: MAP signal (top) acquired together with a pressure measure-ment (bottom) done by pressing a Swan-Ganz catheter against the epi-cardium in the same location and at the same time.

Chapter 3

Analysis of monophasic

action potentials

It is clear from the previous chapter that MAPs are subject to many arte-facts. Therefore up to now analysis of MAPs was mostly done manually. Theadvantage of manual analysis is that there is no risk that artefacts lead tocompletely false results. A manual analysis can therefore be seen as the goldstandard for the analysis of MAPs. However, manual analysis also has somedisadvantages. First of all it is very time consuming. Hence the analysis oflarge data sets, which are often available from electrophysiological experi-ments, is impossible. Second, there can be inter-observer variation. Third,analysis during an experiment (on-line) is impossible. For these reasons wehave developed an algorithm that automatically analyzes large MAP datasets.

In this chapter the manual analysis of MAP signals is first discussed.Then a basic algorithm structure that can be used for automatic MAP pro-cessing is introduced, as well as the corrections that should be implementedin this algorithm for handling artefacts. In a final section the algorithmimplementation is validated against manual analysis of a limited number ofMAPs.

39

CHAPTER 3. ANALYSIS 40

Figure 3.1: MAP recording printed on gridded paper for manual analysis.

3.1 Manual analysis

To illustrate how time consuming manual analysis of MAP signals is, theprocess is described here for the derivation of the APD at 50 % and at 90% repolarization. This is also the process that was used to determine theAPD’s used to validate the automatic processing algorithm (section 3.6).As a first step the MAP signal should be printed on paper with a grid inboth the amplitude and the time direction. For example, an interval of 5 msbetween grid lines can be chosen for the time scale and an interval of 1 mVcan be chosen for the amplitude scale. An example of a MAP measurementon gridded paper is shown in fig. 3.1.

On this sheet, the following steps should be repeated for each MAP:

1. Determine the start of the MAP (upstroke).

2. Determine the peak amplitude of the MAP.

3. Determine the baseline amplitude of the MAP. This is the baselinejust before the MAP starts, as was decided in the previous chapter.

4. Calculate the amplitudes at which the MAP is 50 % and 90 % repo-larized from the peak and baseline amplitude of the MAP.

5. Determine intersection of the MAP signal with the horizontal lines atthe 50 % and 90 % repolarization amplitudes.


peakamplitude

baselineamplitude

90%repolariza5on

50%repolariza5onMAPstart

Figure 3.2: Diagram of a simple MAP, showing the different variables usedin the analysis.

6. Measure the time difference between the start of the MAP and bothintersections determined in the previous step.

Fig. 3.2 shows the different variables that are used in this process.

3.2 Algorithm overview

An automatic MAP processing algorithm implemented on a computer hasto work with digital signals. These signals consist of many samples, eachrepresenting the amplitude that was measured at a certain time point. Thisamplitude and time information is therefore the only information availableto the automatic processing algorithm. When a MAP recording is presentedto the algorithm, it repeats the following steps until the end of the recording(= the last sample) is reached:

1. Search for the start of a MAP: go through all samples until a sample isreached where the amplitude increases significantly. This is the startof the MAP.

2. From the start, determine the peak height of the MAP. This is done bylooking for the point at which the amplitude starts decreasing again.The peak of the MAP is the maximum amplitude that is reached.


3. From the peak, look for the end of the MAP. This is the point at whichthe amplitude stops decreasing significantly.

4. The amplitude at which the MAP is 50 % repolarized can now be cal-culated as the amplitude that is in the middle between the amplitudein diastole and the peak amplitude.

5. The time point at which the MAP is 50 % repolarized can then befound by looking for the point where the signal amplitude becomeslower than the calculated amplitude.

6. The APD50 is calculated as the difference between that time point andthe start of the MAP. Steps 4-5-6 should be repeated to determine theAPD90.

3.3 Artefact handling

The simple algorithm discussed in the previous section will only work onperfect MAP signals. Before the algorithm can work with real MAP signals,a number of problems need to be solved. These problems consist of theartefacts discussed in the previous chapter and some other characteristics ofthe MAP signal that can interfere with automatic analysis. The solution toeach of the issues is discussed below.

Noise The MAP signal can be noisy. The noise is reduced significantlyby decimating the signal with a factor 5. This is comparable to applying alow-pass filter. However there can still be small variations in the baseline.To make sure that these variations are not interpreted as the upstroke ofa MAP, a detection threshold is set. The start of a MAP is only detectedwhen a sample has an amplitude above this threshold.

Varying baseline To compensate for baseline variation from beat tobeat, the baseline amplitude is determined independently for each MAP. Itis calculated as the average of the 20 samples just before the start of the


upstroke of the MAP.

Varying amplitude Apart from variation in the baseline there can alsobe a large variation in the amplitude of the MAP signal. This means thatthere is a variation in the difference between the peak of the MAP and thebaseline. To take this into account, the detection threshold is set dynam-ically. At each time point, it is calculated as the amplitude that is at 70% between the minimum and maximum of a 2 second interval around thatpoint.

Negative terminal deflection When there is a negative terminal de-flection, the algorithm will detect the minimum of the terminal deflection asthe end of the MAP. If this amplitude was used as the baseline this wouldnot be correct. Use of the baseline determination as described above solvesthis problem, as this detects the baseline just before the MAP starts.

Diastolic deflections As diastolic deflections usually have a small am-plitude, they are ignored by the algorithm if the detection threshold is setproperly.

Stimulus artefact A stimulus artefact with high amplitude could bedetected as the upstroke of a MAP if no precautions are taken. Threesafeguards are implemented to prevent this:

1. The decimation of the signal leads to reduction of the amplitude ofthe stimulus artefact, as it is a signal with a high frequency and issmoothed out. This may already yield a stimulus artefact that has anamplitude below the detection threshold.

2. If a peak (presumably a MAP peak) is detected, the algorithm checksif this peak is really the maximum in a 150 ms interval. If a differentmaximum is found, the first peak was probably a stimulus artefact andthe maximum is the MAP peak.

3. The stimulus artefact always has a much shorter duration than a MAP.


If a MAP is detected the total duration is therefore checked. If it isshorter than 150 ms, the MAP is disregarded. If a stimulus artefactis falsely detected as a MAP, its duration will be shorter than theminimum duration and it will not be counted as a MAP.

3.4 Implementation

An advanced algorithm, using the general structure defined in section 3.2and implementing all corrections described in section 3.3 was designed usingMATLAB. In this section the different steps that are implemented in thealgorithm are described in their correct order. A schematic overview of thealgorithm is depicted in the flowchart in fig. 3.3

1. Read data from file. The algorithm was designed to work with thenative EPTracer format.

2. Decimate MAP signal.

3. Determine MAP threshold to start with: set at 70 % of the differencebetween the maximum and minimum amplitude in the first second ofthe recording.

4. Find the first sample that has an amplitude above the MAP threshold,then:

(a) Find the peak of the MAP.

(b) Look for the maximum in a 150 ms interval around the peak. Ifthe maximum is not the peak that was detected, that peak wasprobably a stimulus artefact. The real maximum should then beused as the peak of the MAP.

(c) From the peak, search backward for the start of the MAP.

(d) From the peak, search forward for the end of the MAP.

(e) If the time from start to end is less than 150 ms, the peak underexamination is probably a stimulus artefact. It is disregarded and


Read EPTracer file

Decimate MAP signal

Calculate MAP

threshold

Find next sample above threshold

Find peak of MAP

Check for maximum in

150 ms interval

Find start (backward from peak)

Find end (forward

from peak)

Check duration (> 150 ms)

Calculate baseline

amplitude

Calculate 50 and 90 % repolarization

amplitudes

Find 50 and 90 % repolarization

time points

Calculate APD50 and

APD90

Figure 3.3: Flowchart of the algorithm implemented in MATLAB.


the algorithm restarts at step 3 from the first sample after theend of the stimulus artefact.

(f) Calculate the baseline from the samples just before the start.

(g) Calculate the amplitudes at which the MAP is 50 % and 90 %repolarized using the detected baseline and peak amplitudes.

(h) Find the time points at which the MAP is 50 % and 90 % repo-larized.

(i) Calculate time difference with start (= APD50, APD90).

(j) Determine the threshold for the next MAP: 70 % of the differencebetween the maximum and minimum amplitude in a 2 secondinterval around the end of the current MAP.

(k) Continue at step 3 from the first sample after the end of thecurrent MAP.

5. If the end of the recording is reached when the end of the current MAPis not yet detected, the current MAP is disregarded.

A visualization of an automatic analysis of a MAP recording is shown infig. 3.4.

3.5 Graphical User Interface (GUI)

In order to make the algorithm easy-to-use, a GUI was designed in MAT-LAB. This GUI lets the user select the EPTracer file that was saved fromthe recording device during the experiment. Different channels can be dis-played simultaneously on the screen. The logfile, which contains user notesmade during the experiment, is also displayed. This makes it easy to selectthe time point during the experiment that is of interest to the user. TheMAP processing algorithm can be called using a simple click on the ”Pro-cess MAP” button or it can even be run automatically each time the timeposition is changed. This way the user has a ”live” view of the analysis ofthe MAP signal. The results of the MAP analysis can also be exported toa text file. A screenshot of the GUI is shown in fig. 3.5.


Figure 3.4: Example of an automatically processed MAP recording. Top:the MAP recording with the detected peak (red dot) and baseline amplitude(green line). Bottom: detected APD90 (circle) and APD50 (triangle) of theMAPs in the recording.


Figure 3.5: Screenshot of the GUI that is used for processing of the MAPrecordings.

3.6 Validation

Although the manual analysis of MAP signals has its downsides, it is stillconsidered the gold standard. Therefore the designed algorithm should bevalidated against manual analysis of a MAP recording. This was done for aMAP recording of 12 seconds, recorded while pacing at a cycle length of 400ms. This recording contained a total of 24 complete MAPs. For each MAPthe APD90 and APD50 was determined using the manual method describedin section 3.1 and using the designed algorithm.

A summary of the results can be found in table 3.1. There was goodagreement between the manual and automatic determination of the APD’s,with only a 1.3 % average relative difference between both analyses. Thestatistical significance of this difference was evaluated using a paired Stu-dent’s t-test. The difference was non-significant for both APD90 and APD50(p > 0.05).


Table 3.1: Results of the validation of the algorithm for automatic analysisagainst manual analysis.

APD90 APD50

Average (manual) 131.7 ms 215.8 ms

Average absolute difference 1.7 ms 2.7 ms

Average relative difference 1.3 % 1.3 %

Chapter 4

Application to in-vivo

experiments

The eventual goal of recording and analyzing monophasic action potentialsis the application of this technique to in-vivo experiments. In this chaptera small part of a larger in-vivo study is described. Apart from the MAPrecordings a number of other electrophysiological experiments were also donein this study. However, these measurements are outside of the scope of thisthesis. The purpose of this chapter is to describe an example of the typeof study in which the developed algorithm could be useful. For a completedescription of the study we refer to upcoming publications.

4.1 Introduction

Tetralogy of Fallot is a congenital heart defect that is present in approxi-mately 3 out of 10.000 live births. It is caused by pathological development ofthe infundibular septum of the right ventricle and results in 4 key anatomicfeatures, also shown in fig. 4.1:

1. Overriding aorta.

2. Right ventricular outflow tract (RVOT) obstruction.

50

CHAPTER 4. APPLICATION 51

Figure 4.1: A normal heart and one suffering from Tetralogy of Fallot.

3. Ventricular septum defect (VSD).

4. Right ventricular hypertrophy.

The etiology is unknown and most patients will die during childhood ifno correction is done. Since the 1960’s a surgical correction procedure hasbeen established, which is mostly performed at the age of 3-6 months. Itconsists of the closing of the VSD and relief of the RVOT stenosis. Althoughthis procedure is very successful in repairing the primary defects of the con-dition, some damage during the repair procedure is unavoidable. Most oftena combination of scar tissue in the right ventricle and pulmonary valve in-competence is seen. Both were thought to be harmless in the first decadesafter the introduction of early complete repair for tetralogy patients. How-ever, after 20-30 years many patients develop sequelae from the surgery.The damaged pulmonary valve produces chronic volume overload and di-latation of the right ventricle. This may lead to exercise intolerance. Manypatients also develop arrhythmias and a number of cases of sudden deathhave occurred.


This raises a few questions. First of all what causes the arrhythmias andsudden death? Is it purely the scar tissue? Is it the dilatation of the rightventricle which also causes electrophysiological changes? Or is it a combi-nation of both? Secondly, one should question the timing of the surgicalrepair in relation to the extent of RVOT relief, from both hemodynamicaland electrophysiological point of view. Some surgeons have argued that itmight be better to delay the repair procedure until the right ventricle hasbecome slightly hypertrophic, as a hypertrophic right ventricle might betterwithstand the chronic regurgitation through the pulmonary valve.

One step towards answering these questions is a thorough investigationof how the electrophysiological properties of the right ventricle change aftera period of volume overload or when a scar is induced. As MAPs are avery good tool to investigate the local electrophysiological properties of theheart, we have decided to investigate these changes using MAPs.

4.2 Methods

All experiments were done on pigs. The ethical committee of the UniversityHospital Ghent granted permission for this study. Surgical procedures wereperformed under general anesthesia. Anesthesia was induced with propofol1 % (1mg/kg). Anesthesia maintenance was achieved by sevoflurane inhala-tion (2 % End-Tidal). Intermittent positive pressure mechanical ventilationwas provided by a constant-volume ventilator with a fixed oxygen / air mix-ture (FiO2=0,5). Physiological monitoring was performed in accordancewith the American Society of Anesthesiologists standards.

Three study groups, each containing 4 pigs were created. On each studygroup a specific surgery was performed at the age of 3 months, each de-signed to model one of the possible causes of arrhythmias as described inthe previous section:

1. Isolated scar tissue : a scar was created on the infundibulum, com-parable to the scar created by the repair procedure. The pulmonaryvalve was left intact.


2. Isolated pulmonary regurgitation : partial resection of a pul-monary valve leaflet.

3. Combined scar tissue and pulmonary regurgitation : a transan-nular patch was placed in the RVOT in association with a partialpulmonary valve resection.

All surgical procedures were performed via a right thoracotomy. A fourthstudy group, in which no surgical intervention was done, was used as acontrol.

Three months postoperatively the hearts of the pigs were exposed througha sternotomy and MAP measurements were done on the epicardium. TheMAP measurement electrode and recording setup were the same as describedin section 2.1. To determine the regional electrophysiological changes, MAPswere measured in 4 different locations on the heart: the outflow tract of theright ventricle (RVOT), the inflow tract of the right ventricle (RVIT), theapex of the right ventricle (RVA) and the apex of the left ventricle (LVA).All MAP measurements were done while pacing at a cycle length of 400 msto eliminate the effect of the length of the preceding diastolic interval on theMAP duration. During the experiments blood gas measurements were takenat regular intervals to ensure the results were not corrupted by electrolytedisturbances.

The MAP recordings were analyzed using the GUI described in the pre-vious chapter and APD50 and APD90 were determined for each of the sub-jects. For each study group the statistical significance of the difference inAPD with the control group was evaluated using a Mann-Whitney U-test.A significant result was defined as a result with p < 0.001.

4.3 Results

Sixty-four MAP recordings, containing a total of approximately 800 MAPs,were analyzed in less than one hour. No misdetections were made by thealgorithm, as could be verified visually with the software. Fig. 4.2 shows


*

0

50

100

150

200

250

300

RVIT RVOT RVA LVA

APD

90(m

s)

**

** *

0

50

100

150

200

250

300

RVIT RVOT RVA LVA

APD

50(m

s)

Control PI Scar PI+Scar

Figure 4.2: Average APD50 (top) and APD90 (bottom) for all study groupsand evaluated heart regions (* = significant difference with control group, P< 0.001). Abbreviations: RVOT: right ventricle outflow tract, RVIT: rightventricle inflow tract, RVA: right ventricle apex, LVA: left ventricle apex,PI: pulmonary insufficiency.

the average APD90 and APD50 for each of the evaluated regions and eachof the study groups. Significant differences are marked.

4.4 Discussion

The use of the automatic processing algorithm for the MAPs was a big ad-vantage. All recordings were easily selected from the large recorded datasets using the implemented GUI. Verification of the performance of the al-gorithm could be done on-line while selecting the appropriate time framesof the MAP recordings. Analysis of a 10 second MAP recording only takesapproximately 20 ms, enabling updating of the MAP analysis while scrolling


through the data file. If this analysis would have to be done manually, itwould take much longer.

The brief description of results in this chapter does not warrant extensiveconclusions about the origin of arrhythmias in repaired Tetralogy of Fallotpatients. As mentioned above, the MAP measurements are part of a largerelectrophysiological study which includes other measurements as well. Theresults should therefore be interpreted in conjunction with the rest of thestudy. However, some indications may be derived. When looking at thedifference in MAP duration at 90 % and 50 % repolarization between thecontrol group and the other groups, 3 significant differences are found. Allthree are situated around the right ventricle in- and outflow, which is thearea where the surgery was performed. A significant difference was foundin the study group with a transannular patch and in the study group withan isolated scar in the RVIT. In the RVOT the difference was only signifi-cant for the pigs with a transannular patch. Pigs with isolated pulmonaryinsufficiency had MAP durations that were not significantly different fromthe control group.

In all significant cases the average APD50 and APD90 were smaller thanin the control group. This means that the repolarization of the cardiac cellsoccurs faster in these cases. This change in electrophysiological propertiescould provide substrate for the generation or support of cardiac arrhythmias.Indeed, a faster repolarization means that these cells will have shorter re-fractory period and hence become excitable more quickly than is normal. Inextreme cases this could lead to re-entry or ectopic beats, causing arrhyth-mias or sudden death. If the data obtained from the other measurements inthe study supports similar conclusions, this would point us in the directionthat the problems of repaired Tetralogy of Fallot patients are mainly causedby the scar or the combination of the scar and dilatation, not by dilatationonly.


4.5 Conclusion

The study described in this chapter illustrates the applicability of automaticanalysis of MAP signals in in-vivo studies. However, as the described resultsare only part of a larger study, no definite conclusions can be drawn fromthis data with regard to the origin of arrhythmias in repaired Tetralogy ofFallot patients.

Chapter 5

Conclusion

This master thesis provides an overview of the theory, acquisition methodsand analysis of monophasic action potentials. In the first chapter the MAPwas introduced as an interesting technique to measure local repolarizationproperties of cardiac tissue. The discussion about the origin of the MAP sig-nal, and mainly which electrode is the recording electrode, was summarized.This discussion went on for over 100 years, until finally Vigmond presentedhis theory, supported by computer simulations. It states that both the tipand the reference electrode are needed for MAP recording, and that in anideal MAP the shape of the MAP represents the shape of the transmem-brane action potential in the cardiac cells in the field of view of the referenceelectrode.

The second chapter focused on the MAP measurement setup and theproblems that can arise with MAP recordings. A thorough investigationof four artefacts was performed, aiming to provide an explanation for eachartefact and some pointers on how to handle the analysis of a MAP signalwith artefacts. The first artefact that was investigated was the stimulusartefact, which is caused by far field from the pacing electrode. Then baselinewander was discussed. This artefact is mainly caused by bad electrodecontact, most often between the reference electrode and the blood. As anegative terminal deflection is often seen in MAP measurements but neverin transmembrane action potential measurements, this was also considered

57

CHAPTER 5. CONCLUSION 58

an artefact. It has been argued by some authors that this negative deflectionis caused by movement of the tip electrode. However, we have shown thatthis is unlikely and that the negative terminal deflection is most likely farfield from the T-wave that is picked up by the reference electrode. As a finalartefact small diastolic deflections were investigated. These are most likelycaused by small changes in the pressure on the tip electrode, as suggestedby measurements with a Swan-Ganz catheter on the epicardium. Thesediastolic deflections are so small that they hardly ever cause problems forthe analysis of the signal.

The analysis of MAP signals has mostly been done manually. This hassome downsides as manual analysis is very time-consuming and can alsointroduce inter-observer bias. Therefore an automatic signal processing al-gorithm was introduced in the third chapter. This signal processing algo-rithm uses a number of techniques to ensure that artefacts, such as thosedescribed in the second chapter, do not cause mistakes in the analysis. Thealgorithm was implemented in MATLAB and a GUI was designed to pro-vide an interface that is easy to use. The complete program works with thenative EPTracer file format, so that the user can import electrophysiologicalexperiment data straight into the program without additional conversions.The performance of the algorithm was validated against manual analysis,and no significant difference was found between the manual and automaticanalysis of action potential durations.

The goal of using MAPs is to use this technique to perform in-vivostudies. These studies can produce insights in local electrophysiologicalchanges of the heart, which may lead to clinically relevant conclusions. In thefourth chapter, an example of a study in which MAPs were used is described.Experiments were done on an animal (pig) model of repaired Tetralogy ofFallot, in order to determine the best course of action for patients with thiscongenital heart defect. Although definite conclusions could not be drawnfrom the limited results that were presented - these results are part of alarger study - this description shows that MAPs can provide interestinginformation in in-vivo studies. It also shows that MAPs can be analyzedquickly and easily using the program presented in chapter 3.

CHAPTER 5. CONCLUSION 59

In conclusion, MAPs can be very useful to investigate the local repo-larization properties of cardiac tissue. Because the signals can show manyartefacts, the greatest care should be taken during acquisition to ensure opti-mum signal quality. This can be time-consuming but it will greatly improvethe reliability of the measured data. If high-quality data is acquired, it canbe post-processed reliably with the presented algorithm and GUI.

Bibliography

[1] Burdon-Sanderson J. On the time-relations of the excitatory process inthe ventricle of the heart of the frog. The Journal of Physiology. 1880Jan;.

[2] Schutz E. Elektrophysiologie des Herzens bei einphasischer Ableitung.Monatsschrift Kinderheilkunde. 1936 Jan;.

[3] Wiggers H. Pure monophasic action potentials and their employmentin studies of ventricular surface negativity. Proceedings of the Societyfor Experimental Biology and Medicine. 1936;.

[4] Churney L. An improved suction electrode for recording from the dogheart in situ. Journal of Applied Physiology. 1964 Jan;.

[5] Sjostrand U. A method for intracardiac recording of monophasic actionpotentials in the dog heart in situ. Acta Physiologica Scandinavica. 1966Jan;.

[6] Korsgren M, Leskinen E, Sjostrand U, Varnauskas E. Intracardiacrecording of monophasic action potentials in the human heart. ScandJ Clin Lab Invest. 1966 Jan;18(5):561–4.

[7] Shabetai R, Surawicz B, Hammill W. Monophasic action potentials inman. Circulation. 1968 Aug;38(2):341–52.

[8] Olsson B, Varnauskas E, Korsgren M. Further improved method formeasuring monophasic action potentials of the intact human heart.Journal of Electrocardiology. 1971 Jan;4(1):19–23.

60

BIBLIOGRAPHY 61

[9] Jochim K, Katz L, Mayne W. The monophasic electrogram obtainedfrom the mammalian heart. American Journal of Physiology. 1935 Jan;.

[10] Katz L. The significance of the T wave in the electrogram and electro-cardiogram. Physiological Reviews. 1928 Jan;.

[11] Katz L, Weinmann S. The relation of the T wave to the asynchro-nism between the ends of right and left ventricular ejection. AmericanJournal of Physiology. 1927 Jan;.

[12] Franz M, Schottler M, Schaefer J, Seed WA. Simultaneous recordingof monophasic action potentials and contractile force from the humanheart. Klin Wochenschr. 1980 Dec;58(24):1357–9.

[13] Franz MR. Long-term recording of monophasic action potentialsfrom human endocardium. American Journal of Cardiology. 1983Jun;51(10):1629–34.

[14] Franz MR. Method and theory of monophasic action potential record-ing. Prog Cardiovasc Dis. 1991 Jan;33(6):347–68.

[15] Nesterenko V, Weissenburger J. Experimental evidence for re-interpretation of basis for the monophasic action potential: a new tech-nique with large amplitude and stable transmural signals. Circulation.1995;92(8 Suppl I):299.

[16] Wilson F, MacLeod A, Johnston F. Monophasic electrical responseproduced by the contraction of injured heart muscle. Proceedings ofthe Society for Experimental Biology and Medicine. 1933;30:797.

[17] Eyster J, Meek W, Goldberg H, Gilson W. Potential changes in aninjured region of cardiac muscle. American Journal of Physiology. 1938Jan;.

[18] Eyster J, Gilson W. The development and contour of cardiac injurypotential. American Journal of Physiology. 1946 Jan;.

BIBLIOGRAPHY 62

[19] Franz MR. Current status of monophasic action potential recording:theories, measurements and interpretations. Cardiovascular research.1999 Jan;41(1):25–40.

[20] Kondo M, Nesterenko V, Antzelevitch C. Cellular basis for themonophasic action potential. Which electrode is the recording elec-trode? Cardiovascular research. 2004 Jan;.

[21] Franz M. What is a monophasic action potential recorded by the Franzcontact electrode? Cardiovascular research. 2005 Jan;.

[22] Nesterenko V, Kondo M, Antzelevitch C. Biophysical basis formonophasic action potential. Cardiovascular research. 2005 Jan;.

[23] Vigmond E. The electrophysiological basis of MAP recordings. Car-diovascular research. 2005 Jan;.

[24] Vigmond E, Leon L. Electrophysiological basis of mono-phasic actionpotential recordings. Medical and Biological Engineering and Comput-ing. 1999 Jan;.

[25] Draper M, Weidmann S. Cardiac resting and action potentials recordedwith an intracellular electrode. The Journal of Physiology. 1951Sep;115(1):74–94.

[26] Woodbury L, Woodbury J, Hecht H. Membrane resting and actionpotentials of single cardiac muscle fibers. Circulation. 1950 Jan;.

[27] Hoffman B, Cranefield P, Lepeschkin E, Surawicz B, Herrlich H. Com-parison of cardiac monophasic action potentials recorded by intracellu-lar and suction electrodes. American Journal of Physiology. 1959 Jan;.

[28] Franz M, Burkhoff D, Spurgeon H, Weisfeldt M, Lakatta E. In vitrovalidation of a new cardiac catheter technique for recording monophasicaction potentials. European Heart Journal. 1986 Jan;.

[29] Ino T, Karagueuzian H, Hong K, Meesmann M, Mandel W, Peter T. Re-lation of monophasic action potential recorded with contact electrode

BIBLIOGRAPHY 63

to underlying transmembrane action potential properties in isolatedcardiac tissues: a systematic microelectrode validation study. Cardio-vascular research. 1988 Jan;.

[30] Levine JH, Moore EN, Kadish AH, Guarnieri T, Spear JF. Themonophasic action potential upstroke: a means of characterizing localconduction. Circulation. 1986 Nov;74(5):1147–55.

[31] Franz MR, Flaherty JT, Platia EV, Bulkley BH, Weisfeldt ML. Lo-calization of regional myocardial ischemia by recording of monophasicaction potentials. Circulation. 1984 Mar;69(3):593–604.

[32] Knollmann BC, Katchman AN, Franz MR. Monophasic action potentialrecordings from intact mouse heart: validation, regional heterogeneity,and relation to refractoriness. Journal of Cardiovascular Electrophysi-ology. 2001 Nov;12(11):1286–94.

[33] Olsson SB. Right ventricular monophasic action potentials during reg-ular rhythm. A heart catheterization study in man. Acta Med Scand.1972 Mar;191(3):145–57.

[34] Franz MR, Kirchhof PF, Fabritz CL, Zabel M. Computer analysis ofmonophasic action potentials: manual validation and clinically perti-nent applications. Pacing and Clinical Electrophysiology. 1995 Sep;18(9Pt 1):1666–78.

[35] Yuan S, Wohlfart B, Olsson SB, Blomstrom-Lundqvist C. Clinical ap-plication of a microcomputer system for analysis of monophasic actionpotentials. Pacing and Clinical Electrophysiology. 1996 Mar;19(3):297–308.

Appendix A

Permission to use

copyrighted material

Vincent Keereman

!"#$%&'()*%()+,%)-.)/00",'123-4)

52'%()!"#$%&"'()*(+,%-.(/*00(/*123(

61-7()4-56"7.(8%"9:(;<-56"7.=%=>%"9:?@7%-:A9=97#B(

8-()C-9579#(D77%7<"9(;C-9579#=D77%7<"9?$E79#=F7B(

(

G7"%(C-9579#H(

(

I7%<-JJ-A9(E%"9#7&K((L6"9M('A$(>A%('A$%(-9#7%7J#(-9(#67(>"J5-9"N9E(J$FO75#(A>(4+IJ=(P>(P(5"9(

F7(A>(>$%#67%("JJ-J#"957H(,.7"J7(.7#(<7(M9AQ=(

(

R7J#(Q-J67J(>A%('A$%(#67J-JK(

(

I%A>=(4-56"7.(8%"9:(

(

Michael R Franz, MD, PhD, FHRS

Professor of Medicine and Pharmacology

Georgetown University Medical Center

Director, Arrhythmia Service and Research

VA Medical Center

50 Irving St, NW

Washington, DC 20422

Moblie: +1-202-361-2970

Email: [email protected]

(

S9(+,%()*H(/*00H("#(0/13T(I4H(C-9579#(D77%7<"9(Q%A#71(

(

G7"%(I%A>=(8%"9:H(

(

P("<("(<7&-5".(J#$&79#("#(U679#(V9-@7%J-#'H(QA%M-9E("#(<'(<"J#7%(#67J-J(#6-J(

'7"%=(L67(J$FO75#(A>(#6-J(#67J-J(-J(#67(<7"J$%7<79#("9&("9".'J-J(A>(<A9A,6"J-5(

"5NA9(,A#79N".J=(8A%(#67(-9#%A&$5NA9(P(6"@7(,7%>A%<7&("9(7W#79J-@7(.-#7%"#$%7(

J#$&'H(Q6-56(5A9#"-9J(%7>7%7957J(#A("(.A#(A>('A$%(QA%M=(8A%(5."%-#'(A>(#67(

.-#7%"#$%7(J#$&'H(P(QA$.&(.-M7(#A($J7("9(-..$J#%"NA9(>%A<(A97(A>('A$%(,$F.-5"NA9J=(

P#(5A957%9J(8-E$%7(/(A>('A$%(,",7%(XP9(@-#%A(@".-&"NA9(A>("(97Q(5"%&-"5(5"#67#7%(

#7569-Y$7(>A%(%75A%&-9E(<A9A,6"J-5("5NA9(,A#79N".JZ(,$F.-J67&(-9([$%A,7"9(

\7"%#(]A$%9".(-9(0^_`=(P>(,AJJ-F.7H(5"9('A$(E%"9#(<7(,7%<-JJ-A9(#A($J7(#6-J(

!""#$%&'()*+,-&,.),/,*00.,%),1)*%'1%,%20,3)#&*'",4)&,%2!$+,

,

52'*6,7)#8,

,

9!*.,&0:'&.$8,

,

;!*10*%,900&0<'*,

,

,

,

=!<':0>3?:@,,

;!*10*%,900&0<'*,

,

ABC/D/E,F,G20*%,H*!I0&$!%7,J,/KK5,J,/K!5012,

C0,E!*%0"''*,LMN,

OPPP,G0*%,

KBQG/HA,

,

;!*10*%>900&0<'*R#:0*%>S0,=TF<$:UJJVLJ;!*10*%>900&0<'*R#:0*%>S0@,,

AU,WXV,YZO,MMMXL[,

\U,WXV,O,XXV,YXV[,

,

,

Analysis and Applications of Monophasic Action...

Documents

Transcript of Analysis and Applications of Monophasic Action...