Effects of Polarity for Monophasic and Biphasic Shocks on

Effects of Polarity for Monophasic and BiphasicShocks on Defihrillation Efficacy with anEndocardiai System

MASAHIRO USUI, GREGORY P. WALCOTT, S. ADAM STRICKBERGER,*DENNIS L. ROLLINS, WILLIAM M. SMITH, and RAYMOND E. IDEKER

From the Departments of Medicine and Pathology, Duke University Medical Center, and theEngineering Research Center for Emerging Cardiovascular Technologies of the School ofEngineering, Duke University, Durham, North Carolina; and the 'Department of Cardiology,University of Michigan Medical Center, Ann Arbor, Michigan

USUI, M., ET AL.; Effects of Polarity for Monophasic and Biphasic Shocks on Defihrillation Efficacy withan Endocardiai System. Electrode polarity bas been reported to be one ofthefactoTs that af feet defibrilla-tion efficacy. We studied the influence of polarity on defibrillation efficacy when monophasic and biphasicwaveforms were used with an endocardiai lead system. In six anesthetized pigs, defibrillation catheterswere placed in the right ventricular (RV) apex and at the junction of the superior vena cava (SVC) andright atrium. Monophasic shocks were 6 ms in duration, while for biphasic shocks the first phase was 6ms and the second was 4 ms in duration. Four electrode configurations were tested: H:S, M (the RVelectrode, cathode; the SVC electrode, anode, with a monophasic shock); S:R. M; R:S, B (the RV electrode,first phase cathode; the SVC electrode, first phase anode, with a biphasic shock); S:R. B. Defibrillationprobability of success curves were determined using an up/down protocol requiring 15 shocks for eachconfiguration. For monophasic shocks, total delivered energy at the 50% probability of success point wassignificantly lower when the RV electrode was an anode than when it was a cathode (R:S, M: 24.4 ± 7.4/ [mean ± SD] vs S:R, M: 16.4 ± 5.5 J; P < 0.05). For biphasic shocks, total energy was not affected bypolarity reversal of the electrodes (R:S, B: 8.7 ± 1.4 J vs S:R, B: 8.4 ± 2.5 J; P = NS). The endocardiaielectrode configuration with the RV electrode as an anode requires less energy for defibrillation with amonophasic but not a biphasic waveform. (PACE 1996; 19:65-71)

transvenous defibrillation, polarity reversal, monophasic waveform, biphasic waveform

Introduction

At implantation of implantable cardioverterdefibrillators (ICDs), several factors influence defi-brillation effectiveness including the size^ and lo-cation^ of the defibrillation electrodes, the wave-form '̂̂ and the sequence of delivery^ of the defi-brillation pulse. In patch electrode systems.

Supported in part by the National Institutes of Health researchgrants HL-427B0. HL-44066, by Cardiac Pacemakers, Iuc. (St.Paul, MN), and hy the Japan Foundation of Aging and Health(Tokyo, fapan).

Address for reprints: Raymond E. Ideker, M.D., Ph.D., Cardiac;Rhythm Management Laboratory, Volker Hall G78A, 1670 Uni-versity Blvd., Birmingham. AL 35294-0019. Fax: (205) 975-4720.

Received September 6, 1994; revision December 5, 1994; ac-cepted December 22, 1994.

electrode polarity is another factor reported to af-fect defibrillation efficacy.^"^ Optimal polarity hasheen reported to vary fTom patient to patient so itis recommended that hoth polarities be assessedat the time of ICD implantation/"^ For extemaldefibrillation, electrode polarity does not appearto affect cardiac resuscitation.^° Recent reportssuggest that the defihrillation threshold [DFT) islower with the right ventricular (RV) electrode asan anode than with the RV electrode as a cathodein a catheter-to-subcutaneous patch system in dogswith monophasic and biphasic shocks^^ and in atotally catheter-based system in humans with mo-nophasic shocks.^^ The purpose of this study wasto determine probability of success curves for defi-hrillation in pigs to evaluate whether the electrodepolarity of monophasic and hiphasic shocks af-fects defihrillation efficacy with an endocardiai

PACE, Vol. 19 January 1996 65

USUI, ET AL.

lead system having electrodes in the superior venacava (SVC) and RV.

Methods

This study was approved by the InstitutionalAnimal Care and Use Committee at Duke Univer-sity. It conformed to the guidelines of the Ameri-can Heart Association on Research Animal Useadopted November 11. 1984.

Animal Preparation

Six, 23- to 27-kg pigs were preanesthetizedwith 74 mg/kg ketamine and 0.74 mg/kg acepro-mazine, given intramuscularly. Subsequently, an-esthesia was maintained with sodium pentobarbi-tal by a 10 mg/kg initial intravenous dose followedhy a continuous intravenous infusion of 0.05 mg/kg per minute. Succinylcholine was initially givenat an intramuscular dose of 1 mg/kg and later at0.25-0.5 mg/kg no more than once per hour to de-crease muscle contraction induced by defibrilla-tion shock. Morphine sulfate was initially given atan intramuscular dose of 0.4 mg/kg and later at 0.2mg/kg once per 2 hours to maintain analgesia. Thepigs were intubated with a cuffed endocardiai tubeand ventilated with room air and oxygen through arespirator (Harvard Apparatus, Inc., South Natick,MA, USA). Arterial hlood pressure was monitoredwith a catheter inserted in the femoral artery andconnected to a Statham transducer (Gould, Inc.,Valley View, OH, USA). Blood pressure and a leadII electrocardiogram were continuously displayedon a monitor (VSM, Physio-Control Corp., Red-mond, WA, USA). Rectal temperature was moni-tored continuously and maintained within normallimits with an electric blanket. Normal saline wascontinuously infused through a catheter placed inthe right internal jugular vein. Blood samples weretaken every 60 minutes to determine the pH, P02.Pc;o2. base excess, CO3, HCO;," contents, and cal-cium, potassium, and sodium concentrations. Nor-mal metabolic status was maintained throughoutthe study hy administrating electrolytes andchanging the oxygen concentration of inspired air.

Two 3.4-cm long catheter platinum-coated ti-tanium electrodes, 3.9 cm^ in area (Cardiac Pace-makers, Inc., St. Paul, MN, USA) were used. Onewas inserted from the left external jugular vein and

the other was inserted from the right external jugu-lar vein. These two electrodes were randomly ex-changed for each experiment. The electrodes wereadvanced to the proper position under fluoro-scopic guidance. The SVC electrode was posi-tioned at the right atrial/SVC junction. The RVelectrode was advanced as far as possible into theRV apex. Each catheter was secured with a ligatureat the venotomy site to stabilize its position.

Fibrillation and Defibrillation Procedures

Ventric:ular fibrillation was induced with 60-Hz alternating current delivered through the twodefihriHating catheters. Fibrillation was allowedto continue 10 seconds before a defibrillation testshock was given. Defihrillation testing was per-formed during expiration with the respirator tem-porarily disconnected from the intubation tube. Ifa test shock failed, a rescue shock of higher defi-brillation energy was given immediately throughthe same catheter system. A minimum of 4 min-utes was allowed to elapse before another shockwas tested.

Monophasic or biphasic, fixed duration, trun-cated exponential shocks were generated by a 150-(JLF defibrillator (Ventritex HVS-02, Sunnyvale,CA, USA). Monophasic shocks were 6 ms in dura-tion, while for biphasic shocks the first phase was6 ms and the second was 4 ms in duration (Fig. 1).For biphasic shocks, leading edge voltage of phasetwo (V2L) equaled the trailing edge voltage ofphase one (VlT) (Fig. 1), and the overall tilt variedwith system impedance.

Four electrode configurations were tested(Fig. 2):

1. The RV electrode (R), cathode ( - ) to theSVC electrode (S), anode ( + ), monophasic wave-form (R:S, M);

2. S ( - ] to R ( + ), monophasic waveform (S:R, M);

3. R first phase ( - ) to S, first phase { + ), bi-phasic waveform (R:S, B);

4. S ( - ) to R (-I-), biphasic waveform eachexperiment.

The sequence of order for testing electrodeconfigurations was randomized to account forvariation during the course of the experiment.Each trial consisted of four shocks of these con-

66 January 1996 PACE, Vol. 19

EFFECTS OF POLARITY ON DEFIBRILLATION

Monophasic

6 ms

Biphasic

6 ms-

^-

tV2L1

1V1T1

-—4 ms ^

^—

Figure 1. \Naveforms for defibrillation shocks. The mo-nophasic waveform was 6 ms and the biphasic wave-form was 6/4 ms in duration. For the biphasic waveform,leading edge voltage of phase two (V2L) equaled thetrailing edge voltage of phase one (VlT). Time betweenphases of the biphasic shock was 0.2 ms.

figurations. The four shocks in each trial were de-livered in random order.

A probahility of success method that used anup/down protocol was used to determine defihril-lation efficacy.""^^ An up/down protocol requir-ing 15 shocks was used to determine each defibril-lation prohability of success curve. Counting of the15 shocks was not started until the first reversalin response. The starting voltage was 600 V formonophasic shocks and 400 V for biphasic shocks.Voltage steps of 40 V were used initially. Everytime a shock succeeded, the next test shock wasdecreased hy one step size. Conversely, every timea shock failed, the next shock was increased hyone step size. Step size was reduced to 20 V follow-ing the first reversal of outcome from success tofailure or from failure to success.

At the conclusion of the study, the anesthe-tized animal was terminally fibrillated. The chest

was opened, and the positions of the catheterswere checked to verify their locations. The cathe-ters were removed, and the heart was excised andweighed.

Data Analysis

The actual current and voltage waveforms de-livered to the electrodes were obtained hy isolatingand recording the voltage across a 0.25-ohm resis-tor in series with the electrodes and a 200:1, 100M-ohm resistor divider in parallel with the elec-trodes. These waveforms were digitized at a fre-quency of 20 kHz and recorded by a waveform ana-lyzer (model 6100, Data Precision, Inc., Danvers,MA, USA). Signal analysis software within the an-alyzer was used to calculate the impedance andenergy from the current and voltage measure-ments. The output of the waveform analyzer wasstored in a computerized datafile (Sun Microsys-tems, Inc., Mountain View, CA, USA).

For monophasic shocks, voltage was ex-pressed as leading edge voltage, current as the av-erage current, and energy as the total delivered en-ergy. For biphasic shocks, voltage was expressedas leading edge voltage of phase one, current asthe average current of phase one, and energy the

B

R:S, M

R:S, B

S:R, M

S:R, B

Figure 2. Electrode configurations. A superior venacaval (SVC) electrode (S) was positioned at the rightatrial/SVC junction, and o right ventricular (RV) elec-trode (B) was placed in the RV apex. Four configurationswere tested: R cathode (- )to S anode (+), monophasicwaveform IR:S. M) (ponel A); S (- ) to R (+). monopha-sic waveform (S:R, M) (panel Bj; R first phase (-) to Sfirst phase (—) to R first phase (+ j , biphasic waveform(R:S, B) (panel A}: S first phase (+). biphasic waveform(S:R. B) (panel B).


USUI, ET AL.

sum of the delivered energy of both phases of thetest shock.

For each animal, sigmoid defibrillation proba-bility curves were generated for each measured pa-rameter using probit analysis.^^ The mean values± SD for leading edge voltage, total delivered en-ergy, and average current were determined at the50% and 80% probability of success points foreach configuration. Impedance was calculated byaveraging the data from the 15 shocks for each con-figuration in each animal. The mean values ± SDof impedance were determined for each configura-tion. Repeated measures analysis of variance withthe Student-Newman-Keul's test'^ was used tocompare these variables. Significance was definedas P < 0.05.

Results

The mean heart weight ± SD was 138 ± 22g for six pigs. Voltage, energy, and current at the50% and 80% success points and the impedancefor each configuration are summarized in Table I.

For monophasic shocks, the polarity reversalof the RV electrode from cathode to anode causeda significant decrease in voltage, energy, and cur-rent. At the 50% success point, voltage and currentweredecreasedby 18%, and energy was decreasedby 33%. Polarity reversal did not affect the intere-lectrode impedance.

For biphasic shocks, which were 4 ms longerin total duration than monophasic shocks, voltage,energy, and current all were significantly lowerthan for monophasic shocks. However, polarity re-

versal ofthe RV electrode from first phase cathodeto first phase anode did not significantly affect de-fibrillation efficacy. Although interelectrodeimpedance was slightly higher than it was for mo-nophasic shocks probably because the shock volt-age was lower/^ polarity reversal did not affect theinterelectrode impedance, either.

Discussion

This study compared the influence of polarityon defibrillation efficacy for monophasic and bi-phasic shocks with an endocardial electrode con-figuration. For monophasic shocks, defibrillationenergy requirements were lower when the RV elec-trode was the anode than when it was the cathode.For biphasic shocks, defibrillation energy require-ments were not different whether the RV electrodewas a first anode or a cathode.

Influence of Polarity Reversalfor Monophasic Shocks

Defibrillation energy requirements werelower witb the RV electrode as an anode for mono-phasic shocks. We used two electrodes ofthe sametype as the SVC and RV electrodes. Thus, the re-sults cannot be explained by differences in thesize, surface area, or material of the electrodessince they were the same for both electrodes.Changes in impedance cannot explain tbese re-sults either, because interelectrode impedanceswere not affected by polarity reversal. Therefore,different responses of the myocardium to the two

Configuration

R:S.S:R,R:S,S:R,

MMBB

Effects

Volts

664 :547 :362 I357 z

t 92t 88'b 19"t 48 "

of Polarity or

50% :

Table 1.

1 Defibrillation Probability of

Success

Joules

24.4 :16.4 :8.7 :8.4 :

t 7.4t 5.5*t 1.4"t 2.5"

Amps

8.26 ± 1.286.78 ± 0.99"4.42 ± 0 .51"4.30 ± 0.62"

Volts

720 :602 :395 :406 :

t 91t 75b 58b 74

Success

80%

and Impedance

Success

Joules

27.6' 19.4" 10.1" 10.6

± 7.6± 4.9*+ 3.0"± 4 .0"

Amps

8.66 =7.41 :4.64 :4.75 :

b 1.21b 1.22*t 0 . 67 "b 0 .90 "

ImpedanceOhms

61.7 ± 3.461.9 ± 3.263.0 ± 3.2"62.7 ± 3.0"

Configurations are in Figure 2. Values are mean ± SD." P < 0.05 when compared to R;S. M."* P < 0.05 when comparing S:R, M versus R:S, B, and S:R, M versus S;R, B.

68 January 1996 PACE, Vol. 19


shock polarities must be responsible for the differ-ent defibrillation efficacies.

Schnder et al.*' found that the percentage ofsuccessful defibrillation was slightly higher whenthe upper RV patch was used as an anode thanwhen the left ventricular (LV) apical patch wasused as an anode in dogs. In contrast, Bardy et al.''reported that the DFT in terms of delivered energywas 23% lower when the posterolateral LV patchwas positive than when the anterior RV patch waspositive during clinical implantation of ICDs. Thedifferent results between these studies might beexplained by the different positions of the LVpatch. When the LV patch is placed on the apex,dofibrillation efficacy would be greater with thepatch as a cathode. When the LV patch is placedon the posterolateral wall, defibrillation efficacywould be greater with the patch as an anode. Tha-kur et al ." found that defibrillation energy require-ments were lower when the RV catheter electrodewas an anode than wben the left chest wall subcu-taneous patch was an anode in dogs. Schuder etal.'' found that for transthoracic defibrillation incalves the percentage of successful defibrillationwas higher when the electrode over tbe apex wasa cathode. However, Weaver et al.^" reported thatfor external defibriliation in humans polarity didnot affect the outcomes of cardiac resuscitation.The results of these studies and our study suggestthat defibrillation energy requirements may belower when the electrode attached to the RV isused as an anode or when the left thoracic elec-trode over the apex is used as a cathode, but thatin clinical practice other factors such as longer fi-brillation time or the existence of myocardial in-farction may minimize the effect of polarity on de-fibrillation efficacy.

The experimental results of this study supportthe findings of one family of mathematical modelsof the relationship between shock fields andthe transmembrane potential called bidomainmodels.^"'-'While predicting that a cathode depo-larizes the transmembrane potential of cells imme-diately adjacent to tbe shocking electrode, thesemodels also predict that, beginning 1 to 4 mmaway from the cathode and extending for severalcentimeters or more, the transmembrane potentialis hyperpolarized. Conversely, immediately adja-cent to an anode the transmembrane potential ishyperpolarized, while tissue farther than 1-4 mm

from the anode is depolarized. Recently, hyperpo-larized regions near a cathode (virtual anodes) anddepolarized regions near an anode (virtual cath-odes) were observed experimentally in cardiac tis-sue.^"'^^ Previous experimental results indicatethat the ventricular region from which activationfirst appears after a failed defibrillation shock andin which the shock extracellular potential gradientis weak for the electrode configuration used in thisstudy is the LV apex and LV lateral free wall.^^'^''The bidomain models raise the possibility that thisregion is hyperpolarized when the RV electrode isa cathode and is depolarized when the RV elec-trode is an anode. If we assume similarly that it iseasier to defibrillate depolarized tissue than hy-perpolarized tissue with truncated exponentialwaveforms, defibrillation efficacy should begreater when the RV electrode is an anode, sincethis will cause the tissue in which the shock poten-tial gradient is weak and in which earliest activa-tion appears following failed defibrillation shocksto be depolarized. The results of this study confirmthis prediction. This theory predicts that, if theSVC electrode is placed in the region ofthe innom-inate vein or in the coronary sinus with a totallycatheter-based system, defibrillation efficacyshould still be greater with the RV electrode as ananode because the anode should depolarize the LVapex. However, if an LV patch is placed on theapex or if a left thoracic electrode is placed overthe apex, defibrillation efficacy should be greaterwith the patch or thoracic electrode as a cathodebecause the cathode should depolarize the LVapex underlying the electrode.

Influence of Polarity Reversalfor Biphasic Shocks

As opposed to a monophasic shock, the bipha-sic waveform can depolarize all portions of theventricles. Part of the tissue will be depolarizedduring the first phase of the shock; the remainderof the tissue, which is hyperpolarized during thefirst phase, will be depolarized by the secondphase if the amount of current during the secondphase of the shock is sufficiently large. Reversingthe polarity of a biphasic shock simply inter-changes which portions of the heart are depolar-ized by the first phase and by the second phase.Therefore, in contrast to monopbasic shocks, re-


USUI, ET AL.

versing shock polarity for biphasic shocks wouldnot necessarily be expected to increase defibrilla-tion efficacy if field requirements for defibrillationare lower for depolarized than hyperpolarized tis-sue. The finding in this study that biphasic shockefficacy was not altered by changing shock polar-ity supports this explanation.

Other findings, however, do not support thisexplanation. The biphasic waveform used in thisstudy delivered much more current in the firstphase than in the second phase. According to thisexplanation, reversing the sequence of the twophases should not affect defibrillation efficacy,since with either sequence the two phases of thebiphasic waveform should depolarize all portionsof the ventricles. It has been shown, however, thatreversing the two phases of the biphasic wave-form, so that the amount of current delivered dur-ing the first phase is much smaller than that deliv-ered during the second phase, greatly decreasesdefibrillation efficacy.̂ "̂ "̂ ^

Thakur et al.̂ ^ reported that polarity reversalalso affected defibrillation efficacy for biphasicshocks with the RV-subcutaneous patch configura-tion. Defibrillation energy requirements werelower when the RV catheter electrode was a firstphase anode than when the left chest wall suhcuta-neous patch was a first phase anode. This discrep-ancy between their results and ours suggests thatdifferences in electrode configurations may influ-ence the effect of polarity on bipbasic defibrilla-tion.

References

1. Troup P|, Chapman PD, Olinger GN, et al. The im-planted defibrillator: Relation to defibrillating leadconfiguration and clinical variables to defibrilla-tion threshold. J Am Coll Cardiol 1985: 6:1315-1321,

2. Ideker RE, Wolf PD, Alferness CA, ot al. Currentconcepts for selecting the location, size, and shapeof defibrillation electrodes. PACE 1991; 14:227-240.

3. Winkle RA, Mead RH. Ruder MA, et al. Improvedlow energy defibrillation efficacy in man with theuse of a biphasic truncated exponential waveform.Am Heart J 1989: 117:122-127.

4. Bardy GH, Ivey TD, Allen MD, et al. A prospectiverandomized evaluation of biphasic versus mono-phasic waveform pulses on defibrillation efficacyin humans. ] Am Coll Cardiol 1989; 14:728-733.

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Limitations

Other waveforms of various duration were nottested. For biphasic shocks, a 6/4-ms waveformwas chosen because waveforms with a shorterphase two than phase one duration are more effec-tive for defibrillation.^^-^^ If biphasic waveformswith a longer or shorter second phase duration hadbeen used, polarity reversal migbt have made adifference in defihrillation efficacy. Similarly,other defibrillation electrode configurations werenot tested. Electrode location may also alter theeffects of shock polarity on defibrillation.

ConclusionsThe major findings from this study are: (1) for

monophasic shocks, leading edge voltage, averagecurrent, and total delivered energy at 50% and80% probability of success were significantlylower when the RV electrode was an anode thanwhen it was a cathode with an SVC-RV endocar-dial system in pigs; and (2) for biphasic shocks,50% and 80% probability of success values werenot different whether the RV electrode was a firstphase cathode or anode. Therefore, the configura-tion with the RV electrode as an anode should betested first in clinical DFT testing wben monopha-sic waveforms are used.

Acknowledgments: The atithors would like to thank EllenDixon-TuUoch, Jenny Hagler, Letealia Oliver, and KimberlyMulligan for their technical assistance.

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70 January 1996 PAGE. Vol. 19


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Documents

Effects of Polarity for Monophasic and Biphasic Shocks on