Electrocardiography

“ECG” redirects here. For other uses, see ECG (disam-biguation).“EKG” redirects here. For the album by Edyta Górniak,see EKG (album).Not to be confused with other types of electrography orwith echocardiography.

Electrocardiography (ECG or EKG[lower-alpha 1]) is theprocess of recording the electrical activity of the heartover a period of time using electrodes placed on the skin.These electrodes detect the tiny electrical changes on theskin that arise from the heart muscle's electrophysiologicpattern of depolarizing and repolarizing during eachheartbeat. It is a very commonly performed cardiologytest.In a conventional 12-lead ECG, 10 electrodes are placedon the patient’s limbs and on the surface of the chest.The overall magnitude of the heart’s electrical potentialis then measured from 12 different angles (“leads”) andis recorded over a period of time (usually 10 seconds).In this way, the overall magnitude and direction of theheart’s electrical depolarization is captured at each mo-ment throughout the cardiac cycle.[4] The graph of voltageversus time produced by this noninvasive medical proce-dure is referred to as an electrocardiogram.During each heartbeat, a healthy heart has an orderly pro-gression of depolarization that starts with pacemaker cellsin the sinoatrial node, spreads out through the atrium,passes through the atrioventricular node down into thebundle of His and into the Purkinje fibers, spreadingdown and to the left throughout the ventricles. This or-derly pattern of depolarization gives rise to the character-istic ECG tracing. To the trained clinician, an ECG con-veys a large amount of information about the structureof the heart and the function of its electrical conductionsystem.[5] Among other things, an ECG can be used tomeasure the rate and rhythm of heartbeats, the size andposition of the heart chambers, the presence of any dam-age to the heart’s muscle cells or conduction system, theeffects of cardiac drugs, and the function of implantedpacemakers.[6]

1 History

The etymology of the word is derived from the Greekelectro, because it is related to electrical activity, kardio,Greek for heart, and graph, a Greek root meaning “to

An early commercial ECG device (1911)

Electrocardiography (1957)

write”.Alexander Muirhead is reported to have attached wiresto a feverish patient’s wrist to obtain a record of the pa-tient’s heartbeat in 1872 at St Bartholomew’s Hospital.[7]Another early pioneer was Augustus Waller, of St Mary’sHospital in London.[8] His electrocardiograph machineconsisted of a Lippmann capillary electrometer fixed toa projector. The trace from the heartbeat was projectedonto a photographic plate that was itself fixed to a toytrain. This allowed a heartbeat to be recorded in real time.An initial breakthrough came when Willem Einthoven,working in Leiden, the Netherlands, used the string gal-vanometer (the first practical electrocardiograph) he in-vented in 1901.[9] This device was much more sensi-tive than both the capillary electrometer Waller used andthe string galvanometer that had been invented sepa-rately in 1897 by the French engineer Clément Ader.[10]Einthoven had previously, in 1895, assigned the letters P,Q, R, S, and T to the deflections in the theoretical wave-form he created using equations which corrected the ac-tual waveform obtained by the capillary electrometer tocompensate for the imprecision of that instrument. Usingletters different from A, B, C, and D (the letters used forthe capillary electrometer’s waveform) facilitated com-parison when the uncorrected and corrected lines weredrawn on the same graph.[11] Einthoven probably chose

1

2 2 MEDICAL USES

the initial letter P to follow the example set by Descartesin geometry.[11] When a more precise waveform was ob-tained using the string galvanometer, which matched thecorrected capillary electrometer waveform, he continuedto use the letters P, Q, R, S, and T,[11] and these lettersare still in use today. Einthoven also described the elec-trocardiographic features of a number of cardiovasculardisorders. In 1924, he was awarded the Nobel Prize inMedicine for his discovery.[12]

In 1937, Taro Takemi invented the first portable electro-cardiograph machine.[13]

Though the basic principles of that era are still in usetoday, many advances in electrocardiography have beenmade over the years. Instrumentation has evolved from acumbersome laboratory apparatus to compact electronicsystems that often include computerized interpretation ofthe electrocardiogram.[14]

2 Medical uses

A 12-lead ECG of a 26-year-old male with an incomplete RBBB

The overall goal of performing electrocardiography is toobtain information about the structure and function of theheart. Medical uses for this information are varied andgenerally relate to having a need for knowledge of thestructure and/or function. Some indications for perform-ing electrocardiography include:

• Suspected myocardial infarction (heart attack) ornew chest pain

• Suspected pulmonary embolism or new shortness ofbreath

• A third heart sound, fourth heart sound, a cardiacmurmur[15] or other findings to suggest structuralheart disease

• Perceived cardiac dysrhythmias[15] either by pulse orpalpitations

• Monitoring of known cardiac dysrhythmias

• Fainting or collapse[15]

• Seizures[15]

• Monitoring the effects of a heart medication (e.g.drug-induced QT prolongation)

• Assessing severity of electrolyte abnormalities, suchas hyperkalemia

• Hypertrophic cardiomyopathy screening in adoles-cents as part of a sports physical out of concern forsudden cardiac death (varies by country)

• Perioperative monitoring in which any form of anes-thesia is involved (e.g. monitored anesthesia care,general anesthesia); typically both intraoperativeand postoperative

• As a part of a pre-operative assessment some timebefore a surgical procedure (especially for thosewith known cardiovascular disease or who are un-dergoing invasive or cardiac, vascular or pulmonaryprocedures, or who will receive general anesthesia)

• Cardiac stress testing

• Computed tomography angiography (CTA) andMagnetic resonance angiography (MRA) of theheart (ECG is used to “gate” the scanning so thatthe anatomical position of the heart is steady)

• Biotelemetry of patients for any of the above rea-sons and such monitoring can include internal andexternal defibrillators and pacemakers

The United States Preventive Services Task Force doesnot recommend electrocardiography for routine screen-ing procedure in patients without symptoms and those atlow risk for coronary heart disease.[16][17] This is becausean ECG may falsely indicate the existence of a prob-lem, leading to misdiagnosis, the recommendation of in-vasive procedures, or overtreatment. However, personsemployed in certain critical occupations, such as aircraftpilots,[18] may be required to have an ECG as part of theirroutine health evaluations.Continuous ECG monitoring is used to monitor criticallyill patients, patients undergoing general anesthesia,[15]and patients who have an infrequently occurring cardiacdysrhythmia that would be unlikely to be seen on a con-ventional ten second ECG.Performing a 12-lead ECG in the United States is com-monly performed by specialized technicians that may becertified electrocardiogram technicians. ECG interpre-tation is a component of many healthcare fields (nursesand physicians and cardiac surgeons being the most obvi-ous) but anyone trained to interpret an ECG is free to doso. However, “official” interpretation is performed by acardiologist. Certain fields such as anesthesia utilize con-tinuous ECG monitoring and knowledge of interpretingECGs is crucial to their jobs.One additional form of electrocardiography is used inclinical cardiac electrophysiology in which a catheter isused to measure the electrical activity. The catheter isinserted through the femoral vein and can have severalelectrodes along its length to record the direction of elec-trical activity from within the heart..

3

3 Electrocardiographs

An electrocardiograph with integrated display and keyboard ona wheeled cart

An electrocardiograph is a machine that is used to per-form electrocardiography, and produces the electrocar-diogram. The first electrocardiographs are discussedabove and are electrically primitive compared to today’smachines.The fundamental component to electrocardiograph is theInstrumentation amplifier, which is responsible for tak-ing the voltage difference between leads (see below) andamplifying the signal. ECG voltages measured across thebody are on the order of hundreds of microvolts up to 1millivolt (the small square on a standard ECG is 100 mi-crovolts). This low voltage necessitates a low noise circuitand instrumentation amplifiers are key.Early electrocardiographs were constructed with analogelectronics and the signal could drive a motor to print thesignal on paper. Today, electrocardiographs use analog-to-digital converters to convert to a digital signal that canthen bemanipulated with digital electronics. This permitsdigital recording of ECGs and use on computers.There are other components to the electrocardiograph:[19]

• Safety features that include voltage protection forthe patient and operator. Since the machines arepowered by mains power, it is conceivable that ei-ther person could be subjected to voltage capable ofcausing death. Additionally, the heart is sensitive tothe AC frequencies typically used for mains power(50 or 60 Hz).

• Defibrillation protection. Any ECG used in health-

care may be attached to a person who requires defib-rillation and the electrocardiograph needs to protectitself from this source of energy.

• Electrostatic discharge is similar to defibrillationdischarge and requires voltage protection up to18,000 volts.

• Additionally circuitry called the right leg driver canbe used to reduce common-mode interference (typ-ically the 50/60 Hz mains power).

Typical design for a portable electrocardiograph is a com-bined unit that includes a screen, keyboard, and printer ona small wheeled cart. The unit connects to a long cablethat branches to each lead which attaches to a conductivepad on the patient.Lastly, the electrocardiographmay include a rhythm anal-ysis algorithm that produces a computerized interpreta-tion of the electrocardiogram. The results from thesealgorithms are considered “preliminary” until verifiedand/or modified by someone trained in interpreting elec-trocardiograms. Included in this analysis is computationof common parameters that include PR interval, QT du-ration, corrected QT (QTc) duration, PR axis, QRS axis,and more. Earlier designs recorded each lead sequentiallybut current designs employ circuits that can record allleads simultaneously. The former introduces problems ininterpretation since there may be beat-to-beat changes inthe rhythm that makes it unwise to compare across beats.

4 Electrodes and leads

RL LL

RA LA

RL LL

LARA

RA = Right ArmLA = Left ArmRL = Right LegLL = Left Leg

RA - WhiteLA - BlackRL - GreenLL - Red

Proper placement of the limb electrodes. The limb electrodes canbe far down on the limbs or close to the hips/shoulders as long asthey are placed symmetrically.[20]

A “lead” is not the same as an “electrode”. Whereas anelectrode is a conductive pad in contact with the body thatmakes an electrical circuit with the electrocardiograph, alead is a connector to an electrode. Since leads can sharethe same electrode, a standard 12-lead EKG happens toneed only 10 electrodes (as listed in the table below).

4 4 ELECTRODES AND LEADS

Placement of the precordial electrodes.

A lead is slightly more abstract and is the source of mea-surement of a vector. For the limb leads, they are “bipo-lar” and are the comparison between two electrodes. Forthe precordial leads, they are “unipolar” and compared toa common lead (commonly theWilson’s central terminal),as described below.[21]

Leads are broken down into three sets: limb; augmentedlimb; and precordial. The 12-lead EKG has a total ofthree limb leads and three augmented limb leads arrangedlike spokes of a wheel in the coronal plane (vertical)and six precordial leads that lie on the perpendiculartransverse plane (horizontal).In medical settings, the term leads is also sometimes usedto refer to the electrodes themselves, although this is nottechnically a correct usage of the term, which complicatesthe understanding of difference between the two.The 10 electrodes in a 12-lead EKG are listed below.[22]

Two common electrodes used are a flat paper-thin stickerand a self-adhesive circular pad. The former are typi-cally used in a single ECG recording while the latter arefor continuous recordings as they stick longer. Each elec-trode consists of an electrically conductive electrolyte geland a silver/silver chloride conductor.[23] The gel typicallycontains potassium chloride — sometimes silver chlorideas well — to permit electron conduction from the skin tothe wire and to the electrocardiogram.The common lead, Wilson’s central terminal VW, is pro-duced by averaging themeasurements from the electrodesRA, LA, and LL to give an average potential across the

body:

VW =1

3(RA+ LA+ LL)

In a 12-lead ECG, all leads except the limb leads areunipolar (aVR, aVL, aVF, V1, V2, V3, V4, V5, andV6). The measurement of a voltage requires two con-tacts and so, electrically, the unipolar leads are measuredfrom the common lead (negative) and the unipolar lead(positive). This averaging for the common lead and theabstract unipolar lead concept makes for a more challeng-ing understanding and is complicated by sloppy usage of“lead” and “electrode”.

4.1 Limb leads

The limb leads and augmented limb leads

Leads I, II and III are called the limb leads. The electrodesthat form these signals are located on the limbs—one oneach arm and one on the left leg.[24][25][26] The limb leadsform the points of what is known as Einthoven’s trian-gle.[27]

• Lead I is the voltage between the (positive) left arm(LA) electrode and right arm (RA) electrode:

4.4 Specialized leads 5

I = LA−RA

• Lead II is the voltage between the (positive) left leg(LL) electrode and the right arm (RA) electrode:

II = LL−RA

• Lead III is the voltage between the (positive) left leg(LL) electrode and the left arm (LA) electrode:

III = LL− LA

4.2 Augmented limb leads

Leads aVR, aVL, and aVF are the augmented limb leads.They are derived from the same three electrodes as leadsI, II, and III, but they use Goldberger’s central terminalas their negative pole. Goldberger’s central terminal isa combination of inputs from two limb electrodes, witha different combination for each augmented lead. It isreferred to immediately below as “the negative pole”.

• Lead augmented vector right (aVR)' has the positiveelectrode on the right arm. The negative pole is acombination of the left arm electrode and the leftleg electrode:

aV R = RA− 1

2(LA+ LL) =

3

2(RA− VW )

• Lead augmented vector left (aVL) has the positiveelectrode on the left arm. The negative pole is acombination of the right arm electrode and the leftleg electrode:

aV L = LA− 1

2(RA+ LL) =

3

2(LA− VW )

• Lead augmented vector foot (aVF) has the positiveelectrode on the left leg. The negative pole is a com-bination of the right arm electrode and the left armelectrode:

aV F = LL− 1

2(RA+ LA) =

3

2(LL− VW )

Together with leads I, II, and III, augmented limb leadsaVR, aVL, and aVF form the basis of the hexaxial refer-ence system, which is used to calculate the heart’s elec-trical axis in the frontal plane.

4.3 Precordial leads

The precordial leads lie in the transverse (horizontal)plane, perpendicular to the other six leads. The six pre-cordial electrodes act as the positive poles for the six cor-responding precordial leads: (V1, V2, V3, V4, V5 andV6). Wilson’s central terminal is used as the negativepole.

4.4 Specialized leads

Additional electrodes may rarely be placed to generateother leads for specific diagnostic purposes. Right-sidedprecordial leads may be used to better study pathology ofthe right ventricle or for dextrocardia (and are denotedwith an R (e.g., V5R)). Posterior leads (V7 to V9) maybe used to demonstrate the presence of a posterior my-ocardial infarction. A Lewis lead (requiring an electrodeat the right sternal border in the second intercostal space)can be used to study pathological rhythms arising in theright atrium.An esophogeal lead can be inserted to a part of theesophagus where the distance to the posterior wall ofthe left atrium is only approximately 5–6 mm (remain-ing constant in people of different age and weight).[28] Anesophageal lead avails for a more accurate differentiationbetween certain cardiac arrhythmias, particularly atrialflutter, AV nodal reentrant tachycardia and orthodromicatrioventricular reentrant tachycardia.[29] It can also eval-uate the risk in people with Wolff-Parkinson-White syn-drome, as well as terminate supraventricular tachycardiacaused by re-entry.[29]

An intracardiac electrogram (ICEG) is essentially anECG with some added intracardiac leads (that is, insidethe heart). The standard ECG leads (external leads) are I,II, III, aVL, V1, and V6. Two to four intracardiac leadsare added via cardiac catheterization. The word “electro-gram” (EGM)without further specification usually meansan intracardiac electrogram.

4.5 Lead locations on an ECG report

A standard 12-lead ECG report (an electrocardiograph)shows a 2.5 second tracing of each of the twelve leads.The tracings are most commonly arranged in a grid offour columns and three rows. the first column is thelimb leads (I,II, and III), the second column is the aug-mented limb leads (aVR, aVL, and aVF), and the last twocolumns are the precordial leads (V1-V6). Additionally,a rhythm strip may be included as a fourth or fifth row.The timing across the page is continuous and not tracingsof the 12 leads for the same time period. In other words,if the output were traced by needles on paper, each rowwould switch which leads as the paper is pulled under theneedle. For example, the top row would first trace leadI, then switch to lead aVR, then switch to V1, and thenswitch to V4 and so none of these four tracings of theleads are from the same time period as they are traced insequence through time.

4.6 Contiguity of leads

Each of the 12 ECG leads records the electrical activityof the heart from a different angle, and therefore align

6 6 INTERPRETATION

I Lateral

II Inferior

III Inferior aVF Inferior

aVL Lateral

aVR V1 Septal

V2 Septal

V3 Anterior V6 Lateral

V5 Lateral

V4 Anterior

Diagram showing the contiguous leads in the same color in thestandard 12-lead layout

with different anatomical areas of the heart. Two leadsthat look at neighboring anatomical areas are said to becontiguous.In addition, any two precordial leads next to one anotherare considered to be contiguous. For example, thoughV4 is an anterior lead and V5 is a lateral lead, they arecontiguous because they are next to one another.

5 Electrophysiology

Main article: Cardiac electrophysiology

The formal study of the electrical conduction system ofthe heart is called cardiac electrophysiology (EP). Anelectrophysiology study involves a formal study of theconduction system and can be done for various reasons.During such a study, catheters are used to access the heartand some of these catheters include electrodes that can beplaced anywhere in the heart to record the electrical activ-ity from within the heart. Some catheters contain severalelectrodes and can record the propagation of electricalactivity.

6 Interpretation

Interpretation of the ECG is fundamentally about under-standing the electrical conduction system of the heart.Normal conduction starts and propagates in a predictablepattern, and deviation from this pattern can be a normalvariation or be pathological. An ECG does not equatewith mechanical pumping activity of the heart, for ex-ample, pulseless electrical activity produces an ECG thatshould pump blood but no pulses are felt (and constitutesa medical emergency and CPR should be performed).Ventricular fibrillation produces an ECG but is too dys-functional to produce a life-sustaining cardiac output.Certain rhythms are known to have good cardiac outputand some are known to have bad cardiac output. Ulti-mately, an echocardiogram or other anatomical imagingmodality is useful in assessing the mechanical function ofthe heart.

Like all medical tests, what constitutes “normal” is basedon population studies. The heart rate range of between60 and 100 is considered normal since data shows this tobe the usual resting heart rate.

6.1 Theory

A BA

B

QRS is upright in a lead when its axis is aligned with that lead’svector

PWave

PRSegment

QRSComplex

STSegment

TWave

UWave

PRInterval

QTInterval

Schematic representation of normal ECG

Interpretation of the ECG is ultimately that of patternrecognition. In order to understand the patterns found,it is helpful to understand the theory of what ECGs rep-resent. The theory is rooted in electromagnetics and boilsdown to the four following points:

• depolarization of the heart toward the positive elec-trode produces a positive deflection

• depolarization of the heart away from the positiveelectrode produces a negative deflection

6.3 Rate and rhythm 7

• repolarization of the heart toward the positive elec-trode produces a negative deflection

• repolarization of the heart away from the positiveelectrode produces a positive deflection

Thus, the overall direction of depolarization and repolar-ization produces a vector that produces positive or neg-ative deflection on the ECG depending on which lead itpoints to. For example, depolarizing from right to leftwould produce a positive deflection in lead I because thetwo vectors point in the same direction. In contrast, thatsame depolarization would produce minimal deflection inV1 and V2 because the vectors are perpendicular and thisphenomenon is called isoelectric.Normal rhythm produces four entities— a Pwave, a QRScomplex, a Twave, and aUwave— that each have a fairlyunique pattern.

• The P wave represents atrial depolarization.

• The QRS complex represents ventricular depolar-ization.

• The T wave represents ventricular repolarization.

• The U wave represents papillary muscle repolariza-tion.

However, the U wave is not typically seen and its ab-sence is generally ignored. Changes in the structure ofthe heart and its surroundings (including blood composi-tion) change the patterns of these four entities.

6.2 Electrocardiogram grid

ECG’s are normally printed on a grid. The horizontal axisrepresents time and the vertical axis represents voltage.The standard values on this grid are shown in the adjacentimage:

• A small box is 1 mm x 1 mm big and represents 0.1mV x 0.04 seconds.

• A large box is 5 mm x 5mm big and represents 0.5mV x 0.2 seconds wide.

The “large” box is represented by a heavier line weightthan the small boxes.Not all aspects of an ECG rely on precise recordings orhaving a known scaling of amplitude or time. For ex-ample, determining if the tracing is a sinus rhythm onlyrequires feature recognition and matching, and not mea-surement of amplitudes or times (i.e., the scale of thegrids are irrelevant). An example to the contrary, thevoltage requirements of left ventricular hypertrophy re-quire knowing the grid scale.

One small 1 mm × 1 mm blockrepresents 40 ms time and 0.1 mV amplitude.

One large 5 mm × 5 mm boxrepresents 0.2 seconds (200 ms)time and 0.5 mV amplitude.1 mV (10 mm high)

reference pulse

Amplitude

Time

Measuring time and voltage with ECG graph paper

6.3 Rate and rhythm

In a normal heart, the heart rate is the rate in which thesinoatrial node depolarizes as it is the source of depolar-ization of the heart. Heart rate, like other vital signs likeblood pressure and respiratory rate, change with age. Inadults, a normal heart rate is between 60 and 100 beatsper minute (normocardic) where in children it is higher.A heart rate less than normal is called bradycardia (<60in adults) and higher than normal is tachycardia (>100 inadults). A complication of this is when the atria and ven-tricles are not in synchrony and the “heart rate” must bespecified as atrial or ventricular (e.g., atrial rate in atrialfibrillation is 300–600 bpm, whereas ventricular rate canbe normal (60–100) or faster (100–150)).In normal resting hearts, the physiologic rhythm ofthe heart is normal sinus rhythm (NSR). Normal sinusrhythm produces the prototypical pattern of P wave, QRScomplex, and T wave. Generally, deviation from normalsinus rhythm is considered a cardiac arrhythmia. Thus,the first question in interpreting an ECG is whether ornot there is a sinus rhythm. A criterion for sinus rhythmis that P waves and QRS complexes appear 1-to-1, thusimplying that the P wave causes the QRS complex.Once sinus rhythm is established, or not, the second ques-tion is the rate. For a sinus rhythm this is either the rateof P waves or QRS complexes since they are 1-to-1. Ifthe rate is too fast then it is sinus tachycardia and if it istoo slow then it is sinus bradycardia.If it is not a sinus rhythm, then determining the rhythm isnecessary before proceeding with further interpretation.Some arrhythmias with characteristic findings:

• Absent P waves with “irregularly irregular” QRScomplexes is the hallmark of atrial fibrillation

• A “saw tooth” pattern with QRS complexes is thehallmark of atrial flutter

• Sine wave pattern is the hallmark of ventricular flut-ter

8 6 INTERPRETATION

• Absent P waves with wide QRS complexes with fastrate is ventricular tachycardia

Determination of rate and rhythm is necessary in order tomake sense of further interpretation.

6.4 Axis

The heart has several axes, but the most common by faris the axis of the QRS complex (references to “the axis”implicitly means the QRS axis). Each axis can be compu-tationally determined to result in a number representingdegrees of deviation from zero, or it can be categorizedinto a few types.The QRS axis is the general direction of the ventricu-lar depolarization wavefront (or mean electrical vector)in the frontal plane. It is often sufficient to classify theaxis as one of three types: normal, left deviated, or rightdeviated. Population data shows that normal QRS axis isfrom −30° to 105° with 0° being along lead I and posi-tive being inferior and negative being superior (best un-derstood graphically as the hexaxial reference system).[30]Beyond +105° is right axis deviation and beyond −30° isleft axis deviation (the third quadrant of −90° to −180°is very rare and is an indeterminate axis). A shortcut fordetermining if the QRS axis is normal is if the QRS com-plex is mostly positive in lead I and lead II (or lead I andaVF if +90° is the upper limit of normal).The normal QRS axis is generally down and to the left, fol-lowing the anatomical orientation of the heart within thechest. An abnormal axis suggests a change in the physicalshape and orientation of the heart, or a defect in its con-duction system that causes the ventricles to depolarize inan abnormal way.The extent of normal axis can be +90° or 105° dependingon the source.

6.5 Amplitudes and intervals

All of the waves on an EKG tracing and the intervals be-tween them have a predictable time duration, a range ofacceptable amplitudes (voltages), and a typical morphol-ogy. Any deviation from the normal tracing is potentiallypathological and therefore of clinical significance.For ease of measuring the amplitudes and intervals, anEKG is printed on graph paper at a standard scale: each1 mm (one small box on the standard EKG paper) repre-sents 40 milliseconds of time on the x-axis, and 0.1 mil-livolts on the y-axis.

6.6 Ischemia and infarction

Main article: Electrocardiography in myocardial infarc-tion

Animation of a normal ECG wave

Ischemia or non-ST elevation myocardial infarctions maymanifest as ST depression or inversion of T waves. It mayalso affect the high frequency band of the QRS.ST elevation myocardial infarctions have different char-acteristic ECG findings based on the amount of timeelapsed since the MI first occurred. The earliest signis hyperacute T waves, peaked T-waves due to localhyperkalemia in ischemic myocardium. This then pro-gresses over a period of minutes to elevations of the STsegment by at least 1 mm. Over a period of hours, apathologic Q wave may appear and the T wave will in-vert. Over a period of days the ST elevation will resolve.Pathologic q waves generally will remain permanently.[33]

The coronary artery that has been occluded can be identi-fied in an ST-elevation myocardial infarction based on thelocation of ST elevation. The LAD supplies the anteriorwall of the heart, and therefore causes ST elevations inanterior leads (V1 and V2). The LCx supplies the lateralaspect of the heart and therefore causes ST elevations inlateral leads (I, aVL and V6). The RCA usually suppliesthe inferior aspect of the heart, and therefore causes STelevations in inferior leads (II, III and aVF).

6.7 Artifacts

An EKG tracing is affected by patient motion. Somerhythmic motions (such as shivering or tremors) can cre-ate the illusion of cardiac dysrhythmia.[34] Artifacts aredistorted signals caused by a secondary internal or ex-ternal sources, such as muscle movement or interferencefrom an electrical device.[35][36]

9

Distortion poses significant challenges to healthcareproviders,[35] who employ various techniques[37] andstrategies to safely recognize[38] these false signals. Ac-curately separating the ECG artifact from the true ECGsignal can have a significant impact on patient outcomesand legal liabilities.[39]

Improper lead placement (for example, reversing two ofthe limb leads) has been estimated to occur in 0.4% to4% of all EKG recordings,[40] and has resulted in im-proper diagnosis and treatment including unnecessary useof thrombolytic therapy.[41][42]

7 Diagnosis

Numerous diagnosis and findings can be made basedupon electrocardiography and many are discussed above.The following is an organized list of these and more.Rhythm disturbances/ Arrhythmias:

• Atrial fibrillation & atrial flutter without rapid ven-tricular response

• Premature atrial contraction (PACs) & Prematureventricular contraction (PVCs)

• Sinus arrhythmia

• Sinus bradycardia & sinus tachycardia

• Sinus pause & sinoatrial arrest

• Sick sinus syndrome: bradycardia-tachycardia syn-drome

• Supraventricular tachycardia

• Atrial fibrillation (afib) with rapid ventricularresponse

• Atrial flutter with rapid ventricular response• AV nodal reentrant tachycardia• Atrioventricular reentrant tachycardia• Junctional ectopic tachycardia• Atrial tachycardia

• Ectopic atrial tachycardia (unicentric)• Multifocal atrial tachycardia• Paroxysmal atrial tachycardia

• Sinoatrial nodal reentrant tachycardia

• Torsades de pointes (polymorphic ventricular tachy-cardia)

• Wide complex tachycardia

• Ventricular flutter• Ventricular fibrillation

• Ventricular tachycardia (monomorphic ven-tricular tachycardia)

• Pre-excitation syndrome

• Wolff–Parkinson–White syndrome

Heart block and conduction problems:

• Aberration

• Brugada syndrome

• First-degree AV block, Second-degree AV block(Mobitz I & II), Third-degree AV block

• Left anterior & left posterior fascicular block;bifasciular block and trifasciular blocks

• Incomplete and complete right bundle branch block(RBBB)

• Incomplete and complete Left bundle branch block(LBBB)

• Long QT syndrome

• Right and left atrial abnormality

Electrolytes disturbances & intoxication:

• Digitalis intoxication

• Calcium: hypocalcemia and hypercalcemia

• Potassium: hypokalemia and hyperkalemia

Ischemia and infarction:

• ST elevation and ST depression

• High Frequency QRS changes

• Myocardial infarction (heart attack)

• Non-Q wave myocardial infarction• NSTEMI• STEMI

Structural:

• Acute pericarditis

• Right and left ventricular hypertrophy

• Right ventricular strain / S1Q3T3

10 10 REFERENCES

8 See also• Electrical conduction system of the heart

• Electrogastrogram

• Electropalatography

• Electroretinography

• Heart rate monitor

• Emergency medicine

9 Notes[1] The version with -K-, which is rarer in British En-

glish than in American English, is an early-20th-centuryloanword from the German acronym EKG for Elek-trokardiogramm (electrocardiogram),[1] which reflects thatGerman physicians were pioneers in the field at thetime. Today AMA style and, under its stylistic influ-ence, most American medical publications use ECG in-stead of EKG.[2] The German term Elektrokardiogrammas well as the English equivalent electrocardiogram con-sist of the New Latin/international scientific vocabularyelements elektro- (cognate electro-) and kardi- (cognatecardi-), the latter from Greek kardia (heart).[3] The -K-version is more often retained under circumstances wherethere may be verbal confusion between ECG and EEG(electroencephalography) due to similar pronunciation.

10 References[1] EKG. Oxford Online Dictionaries

[2] American Medical Association, “15.3.1 Electrocardio-graphic Terms”, AMA Manual of Style

[3] Merriam-Webster. “Merriam-Webster’s Collegiate Dic-tionary”. Merriam-Webster.

[4] “ECG- simplified. Aswini Kumar M.D.”. LifeHugger.Retrieved 11 February 2010.

[5] Walraven, G. (2011). Basic arrhythmias (7th ed.), pp. 1–11

[6] Braunwald E. (ed) (1997), Heart Disease: A Textbook ofCardiovascular Medicine, Fifth Edition, p. 108, Philadel-phia, W.B. Saunders Co.. ISBN 0-7216-5666-8.

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Association Electrocardiography and Arrhythmias Com-mittee, Council on Clinical Cardiology; the Ameri-can College of Cardiology Foundation; and the HeartRhythm Society: endorsed by the International So-ciety for Computerized Electrocardiology”. Circula-tion. 115 (10): 1306–1324. PMID 17322457.doi:10.1161/CIRCULATIONAHA.106.180200.

[37] “northstarcpr.com”.

[38] Jafary, Fahim H (2007). “The “incidental” episode ofventricular fibrillation: A case report”. Journal ofMedicalCase Reports. 1: 72. PMC 2000884 . PMID 17760955.doi:10.1186/1752-1947-1-72.

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[40] Incorrect electrode cable connection during electrocardio-graphic recording (2007) Velislav N. Batchvarov, MarekMalik, A. John Camm, Europace, Oct 2007

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11 External links• The whole ECG course on 1 A4 paper fromECGpedia, a wiki encyclopedia for a course on in-terpretation of ECG

• Wave Maven – a large database of practice ECGquestions provided by Beth Israel Deaconess Medi-cal Center

• PysioBank – a free scientific database with physio-logic signals (here ecg)

• EKG Academy – free EKG lectures, drills andquizzes

12 12 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

12 Text and image sources, contributors, and licenses

12.1 Text• Electrocardiography Source: https://en.wikipedia.org/wiki/Electrocardiography?oldid=791703938 Contributors: Kpjas, Bryan Derksen,

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Granger, Celique, ClueBot, Sadm88, Mild Bill Hiccup, Shaun1045, Lbeben, Harland1, Trivialist,Youdiil, Walking Softly, Monobi, NuclearWarfare, Jotterbot, Razorflame, Den Hieperboree, Nawagaththegama, Kcallen78, Berean Hunter,A059970, XLinkBot, Staticshakedown, Facts707, WikHead, MystBot, Dnvrfantj, Toozdaygirl, Addbot, DOI bot, Fieldday-sunday, Mag-nusA.Bot, Diptanshu Das, MrOllie, Dapeda, Curap, LinkFA-Bot, Quercus solaris, Drjnk, Tahmmo, Tassedethe, Alphacolony, Medicellis,Cimiteducation, Tide rolls, Zorrobot, Ske, Legobot, Chaldor, Luckas-bot, Yobot, Mauler90, Donfbreed, Mmxx, Cardcop05, AnomieBOT,Piano non troppo, Bluerasberry, Materialscientist, Citation bot, Maxis ftw, Cjmike, Jmarchn, Obersachsebot, Zad68, JimVC3, Capri-corn42, Biophysiscool, Hyjl, DSisyphBot, HNE3, EdithStarling, Abce2, RibotBOT, ViolaPlayer, Trafford09, GhalyBot, Amitrajpalanand,Captain-n00dle, FrescoBot, Vijaypinu9, Dger, Electrophys, Z0OMD, OgreBot, GunnarK, Pinethicket, Marinov84, RedBot, Serols, James-Grimshaw, Jauhienij, Corinne68, عقیل ,کاشف Arfgab, Ndkartik, Megumegun, Inferior Olive, PRINCE 1983, Reaper Eternal, Vanisheduser aoiowaiuyr894isdik43, Angelito7, Gene Omission, Solzhenitsyn1, Ripchip Bot, Krishnendu4776, Xdaedalus, Liquefier, EmausBot,WikitanvirBot, Reinhold Schäfer, GoingBatty, Dcirovic, Jasonanaggie, Lunagron, JP75, Ronk01, Jer5150, Bamyers99, H3llBot, Unreal7,Erianna, Card Zero, Jay-Sebastos, TyA, Rhynd, Brandmeister, MonoAV, Donner60, Noblesunny, DSITelemetry, Hazard-Bot, Williambq,Matthewrbowker, Dotmed, Liamc91, Mni9791, Pramicy, Jeffo1025, ClueBot NG, Gareth Griffith-Jones, Gosbear, Morgankevinj huggle,Stan3000, Yg12, Khalid Yousuf, ,1991رائد Saistmp, Widr, Abio87, Pluma, HS Offenburg MT, Helpful Pixie Bot, Asimlimbu, Over-damped, Curb Chain, Wbm1058, Tailor-tinker, BG19bot, Roberticus, JaimeTorchiana, Scorpian ad, Crocodilesareforwimps, Neøn, Rayk-waku, NotWith, 220 of Borg, DanielChangMD, Scanbre, Rob Hurt, BattyBot, Yashovardhan Dhanania, Biosthmors, Millennium bug, Dan-luke007, Cyberbot II, Smagers, YFdyh-bot, Khazar2, Dexbot, Bop90, Kenneth.jh.han, JakobSteenberg, Frosty, Kkkchandu, Jamie bisson,Epicgenius, Scareccrow, Liuxv1986, BASA Спасимир, Muzzlenose, Davidirvan, Iztwoz, Tentinator, Peterjin3076, Ricktcb, HaveNoIdea,Sabrina Barton, Ashleyleia, Hamganu, Ugog Nizdast, Rbarraud, BruceBlaus, Schmidt23, Cbecc, Masterkielbaster, Anrnusna, Meteor sand-wich yum, Robevans123, M dhanushkodi, CMcMillan13, Cooker2007, Monkbot, NewEnglandDr, The Last Arietta, AashishAashish,Shubhu dhanke, Poiuytrewqvtaatv123321, Goggledude, Dr.tanjil, Doctor cardiologist, Steffylorzy, Jerodlycett, KasparBot, Sutatstupni,Yahyansari, Gibbh027, Unenthusiastic, ECG niche, Pseudopig, CLCStudent, Composcompos12, Mar11, Wasiq 9320, Dramitvmmcsjh,Halynoor, GreenC bot, Mariodano, Andrea SI-91, PrimeBOT, Justeditingtoday, Zingvin, Chinchorro y atarraya, Stevenscholfield, Magiclinks bot and Anonymous: 643

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