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Resuscitation 84 (2013) 1596– 1603

Contents lists available at ScienceDirect

Resuscitation

j ourna l ho me p age: www.elsev ier .com/ locate / resusc i ta t ion

xperimental paper

lectrical features of eighteen automated external defibrillators: systematic evaluation�

ulvio Kettea,∗, Aldo Locatelli a, Marcella Bozzolaa, Alberto Zoli a, Yongqin Lib,arco Salmoiraghia, Giuseppe Ristagnoc, Aida Andreassi a

AREU Azienda Regionale Emergenza Urgenza (Lombardia Regional Emergency Service), ItalySchool of Biomedical Engineering, Third Military Medical University, Chongqing, ChinaMario Negri Institute for Pharmacological Research, Milan, Italy

r t i c l e i n f o

rticle history:eceived 12 April 2013eceived in revised form 17 May 2013ccepted 17 May 2013

eywords:utomated external defibrillatorsnergyurrentaveform

a b s t r a c t

Aim: Assessment and comparison of the electrical parameters (energy, current, first and second phasewaveform duration) among eighteen AEDs.Method: Engineering bench tests for a descriptive systematic evaluation in commercially available AEDs.AEDs were tested through an ECG simulator, an impedance simulator, an oscilloscope and a measuringdevice detecting energy delivered, peak and average current, and duration of first and second phase ofthe biphasic waveforms. All tests were performed at the engineering facility of the Lombardia RegionalEmergency Service (AREU).Results: Large variations in the energy delivered at the first shock were observed. The trend of currenthighlighted a progressive decline concurrent with the increases of impedance. First and second phaseduration varied substantially among the AEDs using the exponential biphasic waveform, unlike rectilinear

entricular fibrillation waveform AEDs in which phase duration remained relatively constant.Conclusions: There is a large variability in the electrical features of the AEDs tested. Energy is likely not tobe the best indicator for strength dose selection. Current and shock duration should be both consideredwhen approaching the technical features of AEDs. These findings may prompt further investigations todefine the optimal current and duration of the shock waves to increase the success rate in the clinicalsetting.

© 2013 Elsevier Ireland Ltd. All rights reserved.

. Introduction

More than thirty years have elapsed since the first report onhe use of automated external defibrillation into clinical practice.1

ince then, automated external defibrillators (AEDs) have beenidely spread not only in the emergency medical service setting

ut also among lay people in public places.2–7

Technology has been greatly improved and the AEDs adopt biphasic waveform strategy, in contrast to the traditionalonophasic defibrillators, to promote an increased success of defi-

rillation by concurrently reducing the myocardial damage due to

he shock itself.8 Biphasic waves exploit less energy than monopha-ic wave and achieve greater defibrillation efficacy.9–11

� A Spanish translated version of the abstract of this article appears as Appendixn the final online version at http://dx.doi.org/10.1016/j.resuscitation.2013.05.017.∗ Corresponding author at: Via Campanini, 6, 20124 Milano, Italy.

E-mail address: f.kette@areu.lombardia.it (F. Kette).

300-9572/$ – see front matter © 2013 Elsevier Ireland Ltd. All rights reserved.ttp://dx.doi.org/10.1016/j.resuscitation.2013.05.017

Two main types of biphasic waveforms are available: biphasictruncated exponential (BTE) and rectilinear biphasic (RLB). Amongthese, some companies developed some variations, like the pul-satile truncated exponential and the rectangular waveform.12,13

Based on scientific data, the ILCOR recommendations stated that“. . .there is no evidence of greater effectiveness of one biphasic wave-form or device on another”. The guidelines for cardiac arrest and CPRthus recommend that “the initial biphasic shock should be no lowerthan 150 J for BTE and 120 J for RLB”.12,13

Under the clinical point of view, there is as yet no evidenceon the best biphasic waveform nor on the best energy to achievea successful defibrillation.14 Accordingly, companies have devel-oped their own technology and features based on the internationalrecommendations.

Energy has traditionally been the parameter used to estimatethe strength of the shock although it is the current flowing through

the heart that defibrillates the myocytes. Biphasic defibrillatorsmodify the delivered current in relationship to trans-thoracicimpedance. Thus far, however, the precise amount of currentrequired to achieve a successful defibrillation is still unknown. This

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ccounts for the variability of waveforms, peak and average currentnd of the duration of the first and second phase.

We therefore decided to systematically test several com-ercially available AEDs sold on Italian land following a large

nvestment from the National Ministry of Health to the Italianegions for a wide spread diffusion of AEDs in our country.

. Methods

Overall, eighteen AEDs from twelve different manufacturesere tested:

SaverOne (Ami Italia, Napoli, Italy); G3 Pro (Cardiac Science, Bohtell, WA, USA); G5 Pro (Cardiac Science, Bohtell, WA, USA); Lifeline AED (Defibtech, Guilford, CT, USA); Responder AED (General Electric, Schenectady, NY, USA); Sam300P (HeartSine, Belfast, Ireland); Lifepak 1000 (Physio Control, Redmond, WA, USA); Lifepak expess (Physio Control, Redmond, WA, USA); Cardiolife 2100 (Nihon Kohden, Shangai, China); FR2+ (Philips, Eindhoven, Netherlands); FRx (Philips, Eindhoven, Netherlands); FR3 (Philips, Eindhoven, Netherlands); RescueSAM (Progetti, Trofarello, Italy); AED HeartSave (Primedic, Rottweil, Germany); FRED Easy (Schiller, Baar, Switzerland); FRED Easyport (Schiller, Baar, Switzerland); AED Plus (Zoll, Chelmsford, UK); AED Pro (Zoll, Chelmsford, UK).

Tests were performed by using a defibrillator analyzer (Impulse000D, Fluke Biomedical, Everett). This device allows three differ-nt functions: defibrillation, ECG, pacing. Peak and average currentthe maximum and average values of current delivered during thehock) and shock duration were measured in defibrillation mode.ach shock was delivered by the AEDs by increasing sequentiallyhe impedance from 25 ohm (�) up to 200 � by incremental stepsf 25 �. The AED was turned off at every shock and the impedanceas changed. Changes of impedance were obtained through an

mpedance simulator (Impulse 7010D, Fluke Biomedical, Everett).his device allowed variation of impedance since the 7000D models set at fixed 50 � impedance.

Biphasic waveforms were displayed on a 2 channel oscilloscopeTHS720P model, Tektronik, Beaverton) which had a sensitivityrom 5 millivolt (mV) to 50 volt per division (V/div) and a 8 bitertical resolution with a scale of time which can be set from 5anoseconds (ns) to 50 second per division (s/div).

Tests were made at the Engineering Laboratory of the Lombardiaegional Emergency Service. In order to avoid bias measurements,ll test were made by a single biomedical electronic engineer whoonsistently performed all evaluations. All but one tests were con-ucted between January 2012 and May 2012, with the exception of

newly introduced device which came out on the market in sum-er 2012. Measurements of this device were performed at the end

f September 2012. The pads of each model were cut, replaced withuitable plugs and connected to the defibrillator analyzer.

The following parameters were measured at every shock:

Delivered energy (E), [joule].

Peak current of first and second impulse phase (Ip1, Ip2), (A)[ampere].

Average current of first and second impulse phase (Iavg1, Iavg2),(A) [ampere].

84 (2013) 1596– 1603 1597

- Duration of first and second impulse phase (T1, T2) and total dura-tion (Ttot), (ms), [milliseconds].

For measurements we maintained the energy default settings.All tests were repeated three times.

Additional measurements included peak and average voltage,size, weight, time required to analyze the ECG signal and timeelapsed between turning on the AED and the ready-to-shockmoment. These data, however, are not herein presented as theyare part of separate reports. Preliminary results were reported inabstract forms.15–17

3. Results

Highly consistent data in terms of precision of measurementswere registered. Accordingly, due to the negligible standard devi-ation, the data in the tables reported values without the standarddeviation. Overall, there were four types of trends. In the first one,including 6 AEDs, an energy decline ranging from 5 to 36.5% from25 to 200 � was identified. A second group (two defibrillators)showed a raise in energy in relationship to an impedance increasewith, however, a large difference among their percentage energyincrease, from 5 to 26.9%. In a third group four AEDs maintainedapproximately the same energy value at every impedance level. Inthe fourth group there was an initial increase in energy which thendeclined steadily. Overall, despite the large energy variation, themajority of the energy delivered was within the range declared byeach manufacturer for every given impedance level. The results ofenergy measurements are shown in Table 1.

The peak current of the first phase showed marked decreases inall eighteen AEDs concurrent with the increases in impedance value(Fig. 1). The greatest variation was seen in FRED Easyport AED thatdelivered a peak current of 95.5 A at an impedance value of 25 �and ended up with a peak current of 14 A when the impedance was175 �. Conversely, the AED Pro and AED Plus showed a minor rangeof variation by maintaining a relatively low peak value. More specif-ically, the peak current of these two AEDs varied from 25.6 to 8 Afrom 25 to 200 �. The diversity in peak current among the AEDs wasmore evident at low impedance values than at high impedance lev-els. At impedance values greater than 100 �, the peak current wassimilar for all tested AEDs. The second phase peak current showeda similar trend to that of the first one, but Ip2 maintained lowervalues as compared to those of Ip1.

The first and second phase average current delivered during theshocks showed a similar trend to that described for peak current(Fig. 2).

The first phase, second phase and total wave duration variedamong the AEDs in relationship to the impedance (Table 2). Thegreatest variation in the first phase duration was observed in theCardiolife AED. This parameter, indeed, increased from 3.9 ms at25 � to 18.7 ms at an impedance value of 175 �. Instead, the great-est variation in the total duration of the shock was seen in Sam 300P,in which the Ttot varied from 6.5 ms at an impedance value of 25 �to 31.9 ms at an impedance value of 200 �. Fig. 3 represents the FRxwaveform showing a larger variation in time duration in contrastto the AED Plus which maintained the same duration regardless ofthe changes in impedance.

4. Discussion

The Truncated Exponential and the RectiLinear are the most

common biphasic waveforms currently available in the automatedexternal defibrillators. The recommendations of both guidelineson CPR, American Heart Association and European Resuscita-tion Council, however, only relate to the energy that should be

1598 F. Kette et al. / Resuscitation 84 (2013) 1596– 1603

Table 1Comparison of energy values (J) in relationship to impedance. The table reports the measured value, the maximum and the minimum declared by the manufacturer for eachAED.

AED 25 ohm 50 ohm 75 ohm 100 ohm

Manufacturer Model Measured Mindeclared

Maxdeclared

Measured Mindeclared

Maxdeclared

Measured Mindeclared

Maxdeclared

Measured Mindeclared

Maxdeclared

Ami Italia Saver One 148 132 168 148 132 168 146 132 168 146 132 168Cardiac Science G3 230 193 260 200 170 230 182 155 209 168 144 194Cardiac Science G5 235 193 260 235 170 230 206 155 209 186 144 194Defibtech Lifeline AED 154 132 168 152 132 168 153 ND ND 151 132 168General Electric Responder 235 193 260 206 170 230 187 155 209 174 144 194Heart Sine SAM 300 151 135 165 150 135 165 154 135 165 155 135 165Nihon Kohden Cardiolife 2100 125 127 172 145 135 165 156 127 172 160 127 172Philips FR2+ 60 119 161 134 127 172 142 130 176 145 133 176Philips FR3 128 109 147 149 127 172 153 132 178 155 133 180Philips FRx 130 109 147 151 127 172 154 132 178 156 133 180Physio Control Lifepak 1000 196 170 230 200 180 220 198 170 230 198 170 230Physio Control Lifepak Express 195 170 230 200 180 220 199 170 230 199 170 230Primedic HeartSave 159 121 164 308 239 323 351 296 400 333 292 396Progetti Rescue SAM 185 180 220 186 180 220 188 180 220Schiller Fredeasy 154 127 172 154 127 172 152 127 172Schiller Fredeasy port 152 127 172 153 127 172 151 127 172 149 127 172Zoll AED+ 96 81 109 123 105 143 146 126 170 141 125 169Zoll AED Pro 95 81 109 121 105 143 142 126 170 141 125 169

AED 125 ohm 150 ohm 175 ohm 200 ohm

Manufacturer Model Measured Mindeclared

Maxdeclared

Measured Mindeclared

Maxdeclared

Measured Mindeclared

Maxdeclared

Measured Mindeclared

Maxdeclared

Ami Italia Saver One 146 132 168 146 132 168 146 132 168 146 132 168Cardiac Science G3 159 136 184 152 131 176 146 126 170Cardiac Science G5 172 136 184 162 131 176 155 126 170Defibtech Lifeline AED 152 132 168 147 ND ND 143 ND ND 137 ND NDGeneral Electric Responder 164 136 184 156 131 176 151 126 170Heart Sine SAM 300 155 135 165 157 135 165 158 135 165 157 135 165Nihon Kohden Cardiolife 2100 161 127 172 164 127 172 171 127 172 148 127 172Philips FR2+ 150 137 185 146 133 176 141 128 174Philips FR3 158 135 183 159 136 184 157 134 182Philips FRx 157 135 183 158 136 184 156 134 182 150 ND NDPhysio Control Lifepak 1000 197 170 230 196 170 230 196 170 230 196 170 230Physio Control Lifepak Express 199 170 230 199 170 230 199 170 230 198 170 230Primedic HeartSave 305 267 361 281 246 333 258 228 309 239 ND NDProgetti Rescue SAM 188 180 220 188 176 224 188 176 224Schiller Fredeasy 153 127 172 148 127 172 142 127 172Schiller Fredeasy port 144 127 172 139 127 172 133 127 172Zoll AED+ 132 116 157 124 108 146 113 101 137 107 ND NDZoll AED Pro 131 116 157 122 108 146 113 101 137 105 ND ND

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dttltslihitrfmciorceso

D, not declared; Min declared, minimum energy value declared by the manufactuhe missing data refer to those AEDs that did not deliver the shock at the impedanc

elivered being slightly different from BTE (no lower than 150 J)o RLB (no lower than 120 J). Based on these recommendations,he AED manufactures defined different settings of default energyevel. By measuring every device we identified four different energyrends: a steady decline, a progressive increase, an approximatelytable value and a dual response characterized by an increase fol-owed by a decrease of energy concurrent with the increase inmpedance. Overall, several AEDs delivered an amount of energyigher than the recommended values raising up to more than 300 J

n one model. Other devices delivered energy values lower thanhe minimum limit indicated by the guidelines throughout theange of impedance (from 25 to 200 �). It is likely that these dif-erences are related to the engineering solutions chosen by each

anufacturer. A high energy delivery, however, does not imply aomparable amount of current delivered during the shock. Indeed,t has to be taken into account that energy depends also on the timever which the shock is given. According to its mathematical rep-esentation (E =

∫ t

t0 i2.R dt, which is the integration of the square

urrent multiplied by the resistance over time) a high amount ofnergy may be either the result of high current delivered in a veryhort time or the result of low current given over a longer periodf time. This concept accounts for the reason why energy is not

ax declared, maximum energy value declared by the manufacturer.es of 25 and 200 �. Standard deviation not reported because of negligible values.

the proper parameter to indicate the “strength” of the dischargeand, ultimately, of the appropriate measure of shock effectiveness.These observations were already reported in earlier studies18–20

and have been re-emphasized by more recent investigations.21–23

Despite these observations, joules have traditionally remained theunit of the shock “strength”.

The current is delivered by the capacitor which is the principalcomponent of AED electronic circuit. It can store a different quantityof energy and can deliver the current through the resistance of thecircuit. This is related to the capacitor capacitance (in term of Faradunit), and to trans-thoracic resistance (in term of Ohm unit).

The first phase peak current is the highest value of current deliv-ered by the capacitor. In our measurements we observed that itlargely varied among the AEDs with differences that were moreevident at low impedance than at higher impedance. The effects ofvery high peak current at low impedance are unknown althougha previous study by Lerman indicated an optimal amount of cur-rent ranging between 30 and 40 A.24 At an impedance value of

100 �, which is consistent with the majority of human impedancelevels,25–27 all AEDs were much below 30 A with the exception ofthe Fred Easy and Fred Easyport which had a peak current of 37.2and 32.6 A respectively. Comparable trends were observed in the

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Table 2Comparison of AED first and second phase duration in relationship to impedance.

AED Ami Italia Saver One Cardiac Science G3 Cardiac Science 5 Defibtech Lifeline AED General ElectricResponder

HeartSine Sam300P

Nihon KohdenCardiolife 2100

Philips FR2+ Philips FR3

Ohm T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt

25 4.4 5.7 10.5 3.2 3.2 6.9 3.2 3.2 6.9 2.9 2.9 6 3.2 3.2 7 3.1 3 6.5 3.9 4.3 8.4 2.8 2.8 5.8 2.8 2.8 5.850 6.1 4 10.5 4.5 3.2 8.2 4.5 3.2 8.2 4.2 4.2 8.6 4.4 3.2 8.3 4.6 4.5 9.5 6.3 4.1 10.6 4.1 4.1 8.4 4.5 4.5 9.275 6.8 3.3 10.5 5.7 3.2 9.4 5.7 3.2 9.4 5.8 3.9 9.9 5.7 3.2 9.5 6.6 6.5 13.5 8.8 4.3 13.3 7.2 4.8 12.2 6.3 5 11.5

100 8.7 4.1 13.2 6.9 3.2 10.6 6.9 3.2 10.6 9 6 15.2 6.9 3.2 10.7 8.1 8 16.5 11.3 4.3 15.8 8.9 6 15.1 7.9 5.3 13.4125 10.6 5 16 8.2 3.2 11.9 8.2 3.2 11.9 12.1 8.1 20.4 8.2 3.2 12 10.6 10.5 21.5 13.8 4.3 18.3 12 8 20.2 9.7 6.4 16.3150 12.5 5.8 18.7 9.4 3.2 13.1 9.4 3.2 13.1 12.1 8.1 20.4 9.4 3.2 13.2 12.1 12 24.5 16.3 4.4 20.9 12 8 20.2 11.4 7.6 19.2175 14.4 6.7 21.5 10.7 3.2 14.4 10.7 3.2 14.4 12.1 8.1 20.4 10.6 3.2 14.5 14.3 14 28.7 18.7 4.4 23.3 12 8 20.2 12 8 20.2200 16.3 7.6 24.3 12.1 8.1 20.4 15.6 15.5 31.9 20.9 21.1

AED Philips FRx Physio ControlLifepak 1000

Physio ControlLifepak Express

Primedic HeartSave Progetti Rescue Sam Schiller Fredeasy Schiller Fredeasy port Zoll AED Plus Zoll AED Pro

Ohm T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt T1 T2 Tt

25 2.9 2.9 5.6 3.8 9.6 5.6 3.8 10.2 4.9 4.9 10 6.1 4 10.3 6 4 10.250 4.6 4.6 9.4 7.4 5 12.6 7.4 5 13.2 11.3 3.7 15.2 7.9 5.9 14 4.2 3.2 7.6 5.1 4.9 10.2 6 4 10.2 6 4 10.275 6.3 5 11.5 8.6 5.8 14.6 8.6 5.8 15.2 11.3 3.7 15.2 7.9 5.9 14 4.2 3.2 7.6 5.4 4.2 9.8 6 4 10.2 6 4 10.2

100 8.1 5.4 13.7 9.7 6.5 16.4 9.6 6.4 16.8 11.2 3.7 15.1 7.9 7.9 16 4.2 3.2 7.6 6 3.6 9.8 6 4 10.2 6 4 10.2125 9.8 6.5 16.5 10.4 7 17.6 10.4 7 18.2 11.2 3.7 15.1 9.9 9.9 20 4.4 3.2 7.8 6.1 3.3 9.6 6 4 10.2 6 4 10.2150 11.5 7.7 19.4 11.1 7.4 18.7 11.1 7.4 19.3 11.2 3.7 15.1 11.9 9.9 22 4.4 3.2 7.8 6.1 3.3 9.6 6 4 10.2 6 4 10.2175 12 8 20.2 11.7 7.8 19.7 11.7 7.8 20.3 11.2 3.7 15.1 11.9 9.9 22 4.4 3.2 7.8 6.1 3.3 9.6 6 4 10.2 6 4 10.2200 12 8 20.2 12.2 8.2 20.6 12.2 8.2 21.2 11.2 3.7 15.1 6 4 10.2 6 4 10.2

T1, first phase duration; T2, second phase duration; Tt, total duration of the shock (milliseconds).The missing data refer to those AEDs that did not deliver the shock at the impedance values of 25 and 200 �. Standard deviation not reported because of negligible values.

1600 F. Kette et al. / Resuscitation 84 (2013) 1596– 1603

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ig. 1. Upper panel: variation of first phase peak current in relationship to impedanncrease. Standard deviation not reported because of negligible values.

verage intensity although the differences among the AEDs wereess pronounced.

Previous studies by Kerber stated that excessive current mayause morphologic and functional damage to myocardial cells.owever, his study did not report whether it was a high peak or

high average current that caused these detrimental effects.18 Yet,is and other studies did not report if there was a critical thresholdbove which damage to the cells occurs.28,29 The effects of differ-nt levels of the defibrillation current in human fibrillating hearts,owever are, as yet, largely unknown.

Shock duration is the other variable that makes defibrillationore or less effective. To achieve successful defibrillation, a the-

retical model described by Kroll estimated that the ideal pulseuration for first phase of a biphasic shock should be comprisedetween 3.8 and 10.2 ms in a range of impedance from 40 to00 ohm by using a capacitor of 100–150 microFarad (�F).22 Aore precise duration of the first phase was demonstrated by Shan

t al. in a guinea pig model of ventricular fibrillation. These authorsemonstrated that the highest proportion of successfully defibril-

ated animals was achieved when the duration of the first phaseas set at 5 ms.30

The optimal duration of the first phase depends on the timeonstant of the myocardial cells. Since the cell membrane cane considered like a capacitor, the cell model consists in a RC

Resistance–Capacitance) electric circuit characterized by a timeonstant � (tau) related to capacitance and to resistance. The mem-rane response depends on the cell time constant and, typically,or exponential waveforms, it reaches a maximum value and then

ease; lower panel: variation of second phase peak current in relation to impedance

it decreases. The phase duration is optimized when it is truncatedat the time in which the membrane response reaches its maximumlevel. Shorter or longer phase duration determines a reduced waveeffectiveness leading in turn to waste of current.22 Previous animaland human studies demonstrated that the time constant rangesbetween 2 and 5 ms.22,31

The modern generation of AEDs adjusts defibrillation output bymeasuring the trans-thoracic impedance before the shock deliv-ery. Our data indeed highlighted that the duration of the firstand second phase of the two main types of waveforms, BTE andRLB, act differently by using two different methods of impedancecompensation32: time-based compensation and current-basedcompensation. The AEDs that use the first method act by increas-ing the shock duration according to the changes in impedance. Inthe second method the devices maintain a fixed shock duration atevery impedance values.29

Typically the BTE waveforms use the time-based compensationmethod. Our measurements showed a raise of first and secondphase duration in relationship to the increases in impedance. Onthe other hand, all devices that use a RLB waveform showed analmost unchanged durations for both first and second phase atevery impedance level.

In their respective studies Gliner and Feeser demonstrated thatdefibrillation is more effective when the first phase is equal to or

longer than the second phase.9,33 However, Matula demonstratedthat the defibrillation success decreases when the total durationof the wave increases above 16 ms.31 With respect to these find-ings, our data showed a large difference among the AEDs. At an

F. Kette et al. / Resuscitation 84 (2013) 1596– 1603 1601

Fig. 2. Upper panel: variation of first phase average current in relationship to impedance increase; lower panel: variation of second phase average current in relation toimpedance increase. Standard deviation not reported because of negligible values.

Fig. 3. FRx = AED Philips model FRx. AED Plus = AED Zoll model AED Plus. Upper row: variation of shock duration in relationship to impedance increase. Lower row: AEDspattern which maintain the same shock duration at every impedance level.

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mpedance value equal to 100 � only two defibrillators showed total shock duration greater than the “limit” indicated by Mat-la. At the same time, when the impedance value rose up to 200 �ll devices using a BTE waveform showed a total shock durationreater than 16 ms.

Impedance thus represents a critical issue to achieve a suc-essful defibrillation. Kerber and Dalzell in their previous andndependent studies reported that the range of the trans-thoracicuman impedance did not exceed 160 �.34,35 However, moreecent studies by Chen reported measurements of human trans-horacic impedance much higher than 200 �.36 These findings aref paramount importance since AEDs should be able to detectmpedance levels higher that 200 ohm in order to deliver a shock.nstead we identified some AED which was not able to detect thenderlying rhythm when impedance was set at 200 ohm. In these

nstances these devices vocally prompted to connect the electrodess they were not able to detect the ECG signal. A similar behavioras seen at an impedance value of 25 �. This, however, might be

less critical issue because the AEDs are usually equipped withhe special pediatric paddles which support very low impedances.ediatric pads, however, were not tested in our measurements.

A previous study by Achleitner and coworkers compared seven-een defibrillators the majority of which (14/17) were monophasic

anual defibrillators and two were semi-automated monophasicefibrillators.37 However, the goal of their study was to comparehe selected energy and the delivered energy in relationship to thempedance increase. There is no mention on the real current deliv-red. In their second study four biphasic defibrillators (two manualnd two semi-automated) were tested by reporting the result val-es of energy, initial voltage, initial current, waveform duration andilt. These results were obtained by using a mathematical softwarehat analyzed the shock waveforms previously recorded. Accord-ngly, they did not measure directly those parameters, but theyather calculated them.38

The present work has some limitations: firstly, the tests wereade on the bench only, secondly, our evaluation did not consider

very AED presently available in the world.Another issue is the absence of the pads replaced by the plugs.

he characteristics of the electrode pads and how they modify cur-ent and duration of waveforms vary among manufacturers andads may not necessarily be made by the company that man-factured the defibrillator itself. Indeed, as previously reported,rans-thoracic impedance (TTI) relies on patient impedance and onhe skin/pad contact.39,40 We reasoned that the total TTI value was

ore appropriated to ascertain the effective current delivered as itonsiders both TTI components. Nevertheless, this issue could behe subject of further investigations.

As we are not aware of previous studies on restoration of sponta-eous cardiac function following defibrillation with different levelsf current applied to a defibrillating heart, our data may prompturther investigations in animal models in order to ascertain thempact of the shocks on the success of defibrillation by usingifferent current intensity and different time durations for both firstnd second phase. Our comparison could also be used by the man-factures to improve the technical features of their devices owingo the potential advantage of a systematic unbiased assessment of

large number of AEDs worldwide marketed.

. Conclusion

There are marked differences in energy, current delivered, firstnd second phase duration among the AEDs.

Several studies proposed that defibrillators should be current-ased rather than energy-based. We fully support this concept.eside the current the time duration represents the other vari-ble to be taken into account in order to achieve the maximal

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84 (2013) 1596– 1603

defibrillation effectiveness. These variables should be separatelyconsidered such as to precisely quantify them. This should allow todeliver a high current within an appropriate time interval. Addi-tional experimental and subsequent clinical data are warrantedto apply our results in the experimental and subsequently in theclinical setting.

Conflict of interest statement

The authors state the absence of any conflict of interest.

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