895

Impact of Biphasic Electrical Cardioversion of Atrial Fibrillationon Early Recurrent Atrial Fibrillation and Shock Efficacy

STEPHANOS SIAPLAOURAS, M.D., AXEL BUOB, M.D., CARSTEN ROTTER,MICHAEL BOHM, M.D., and JENS JUNG, M.D.

From Klinik fur Innere Medizin, Kardiologie, Angiologie und Internistische Intensivmedizin, Universitatsklinikumdes Saarlandes, Homburg/Saar, Germany

Impact of Biphasic Cardioversion on ERAF and Efficacy. Introduction: Early recurrent atrialfibrillation (ERAF) after external cardioversion of atrial fibrillation (AF) occurs in 12% to 26% of patients.Whether biphasic cardioversion has an impact on the incidence of ERAF after cardioversion of AF isunclear.

Methods and Results: Consecutive patients (n = 216, mean age 66 years, 71% male, 88% with structuralcardiovascular disease or hypertension) underwent cardioversion with a biphasic (Bi) or monophasic (Mo)shock waveform in randomized fashion. Energies used were 120-150-200-200 Ws (Bi) or 200-300-360-360Ws (Mo). The two study groups (Bi vs Mo) did not differ with regard to age, sex, body mass index, underlyingcardiovascular disease, left atrial diameter, left ventricular ejection fraction, duration of AF fibrillation,and antiarrhythmic drug therapy. Mean delivered energy was significantly lower in the Bi group (Bi:186 ± 143 Ws vs Mo: 324 ± 227 Ws; P < 0.001). Overall incidence of ERAF (AF relapse within 1 minuteafter successful cardioversion) was 8.9% and showed no difference between the two groups (Bi: 8.1% vsMo: 9.7%, P = NS). Cardioversion was successful in 95.4% of patients. The success rate was comparablein both groups (Bi: 94.3% vs Mo 96.8%; P = NS). First shock efficacy did not differ between Bi and Mo(76.4% vs 67.7%; P = NS). Mean number of shocks were 1.4 shocks per patient in both groups.

Conclusion: Biphasic cardioversion allows comparable success rates with significantly lower energies.However, the incidence of ERAF is not influenced by biphasic cardioversion. With the energies used, biphasicand monophasic shock waveforms are comparable with regard to first shock and cumulative shock efficacy.(J Cardiovasc Electrophysiol, Vol. 15, pp. 895-897, August 2004)

electrical cardioversion, early recurrent atrial fibrillation, atrial fibrillation, biphasic

Introduction

Atrial fibrillation (AF) is the most common sustained ar-rhythmia, accounting for 30% to 40% of hospitalizations dueto a cardiac rhythm disturbance.1,2 Electrical cardioversionis an effective, safe, and established method to convert AFinto sinus rhythm. The reported success rates after externalmonophasic cardioversion are between 67% and 90%.3-7 Theincidence rates reported for the early relapse of atrial fibril-lation (ERAF) are 12% to 26% after external monophasiccardioversion.7-9 Improvement of cardioversion success hasbeen reported after alternating electrode placement,10 activepressure on electrodes,11 fluoroscopic paddle control,12 andantiarrhythmic drug therapy.13 A reduction of the incidenceof ERAF has been shown by repeated shock delivery,7,9 an-tiarrhythmic drug therapy,7,8 and overdrive pacing.14

In clinical practice, commercially available biphasic exter-nal defibrillators are gaining more importance. First studiesshowed that biphasic shock waveforms might have advan-tages compared to conventional monophasic damped sinu-soidal shock waveforms. A higher cumulative efficacy for

Address for correspondence: Stephanos Siaplaouras, M.D., Klinik fur In-nere Medizin, Kardiologie, Angiologie und Internistische Intensivmedizin,Universitatsklinikum des Saarlandes, D-66421 Homburg, Germany. Fax:49-6841-1623394; E-mail: siaplaouras@aol.com

Manuscript received 15 January 2004; Accepted for publication 22 March2004.

doi: 10.1046/j.1540-8167.2004.04027.x

converting ventricular fibrillation and AF,15,16 a higher firstshock efficacy,17,18 and less energy requirement of biphasiccompared to monophasic shock waveforms16,17 have been re-ported. However, the impact of biphasic cardioversion on theincidence of ERAF after external cardioversion of AF hasnot yet been investigated. Therefore, the aim of this studywas to compare a rectilinear biphasic shock waveform (Bi)with a conventional damped sinusoidal monophasic shockwaveform (Mo) with regard to the incidence of ERAF andthe shock efficacy of external cardioversion of AF.

Methods

Study Group

Consecutive patients referred to our hospital for electivecardioversion of symptomatic persistent AF following thedefinition of Fuster et al.19 were included in the study.

Exclusion criteria were an acute cardiopulmonary de-compensation, significant electrolyte imbalance (potassium<3.5 or >5.0 mM), a reversible cause of AF (e.g. hyperthy-roidism), ineffective anticoagulation during the last 4 weeksprior to cardioversion (international normalized ratio [INR]target range: 2–3), and an AF duration >1 year.

Electrical Cardioversion

Administration of the established chronic antiarrhythmictherapy was not interrupted for the procedure. All patients gota venous access. Blood pressure, ECG, and oxygen satura-tion were monitored continuously throughout the procedure

896 Journal of Cardiovascular Electrophysiology Vol. 15, No. 8, August 2004

and for at least 3 hours after cardioversion. A standardizedanteroposterior position of the self-adhesive cardioversionpads was achieved following the manufacturer’s instructions(anterior right parasternal, posterior left subscapular). Theprocedure was performed with patients in deep sedation usingintravenous (IV) midazolam (5 mg initially with increasingdosage, and additional fentanyl 0.05–0.1 mg IV if neces-sary). R wave synchronized electrical cardioversion usingan external defibrillator (Bi: Zoll M-series biphasic, ZollMedical Corp., Burlington, MA, USA; Mo: Zoll M-seriesmonophasic, Zoll Medical Corp.) was performed with in-creasing energies up to the maximum output of each defibril-lator (Bi: 120-150-200-200 Ws; Mo: 200-300-360-360 Ws).Active pressure was applied on the anterior pad by the at-tending physician.

Successful cardioversion was defined as termination ofAF with at least two consecutive sinus beats. ERAF was de-fined as a relapse of AF within 1 minute after a successfulcardioversion.

Statistical Analysis

All data are presented as mean ± SD. To compare continu-ous variables of groups, the Student’s t-test or Mann-Whitneyrank sum test was used. To compare categorical variables, theChi-square and Fisher’s exact test were used. P < 0.05 wasconsidered statistically significant.

Results

Study Population

Two hundred sixteen patients who fulfilled the crite-ria discussed earlier were included. The characteristicsof the patients, predominant cardiovascular diseases, andchronic antiarrhythmic treatment are summarized in Table 1.There were no statistically significant differences between

TABLE 1

Baseline Characteristics of the Patients (n = 216)

Mo Bi P Value

Clinical characteristicsAge (years) 65 ± 10 66 ± 10 NSSex (M/F) 72/28% 71/29% NSBody mass index 27.4 ± 4 27.9 ± 4 NSDuration of AF (months) 3.2 ± 4 4.1 ± 10 NS

LVEF (%) 62 ± 15 59 ± 13 NSLA diameter (mm) 48 ± 6 48 ± 7 NSPredominant cardiovascular disease

Arterial hypertension (%) 31 34 NSValvular disease (%) 27 23 NSCoronary artery disease (%) 17 20 NSCardiomyopathy (%) 11 10 NSLone AF (%) 13 12 NSPostoperative ASD (%) 1 1 NS

Antiarrhythmic drug therapy at the time of cardioversionClass I (%) 9 6 NSClass II (%) 23 39 NSSotalol (%) 26 17 NSAmiodarone (%) 28 29 NSClass IV (%) 0 1 NSDigitalis (%) 7 4 NSNo antiarrhythmic therapy (%) 7 4 NS

AF = atrial fibrillation; ASD = atrial septal defect; Bi = biphasic shockwaveform; LA = left atrium; LVEF = left ventricular ejection fraction;Mo = monophasic shock waveform.

67

26

61

77

127 4

0

20

40

60

80

100

1 2 3 4

Mo Bi

Mean: Mo: 1.4 ± 0.7Bi: 1.4 ± 0.8p = ns

%

Per

cent

ofpa

tien

ts

Number of shocks

Figure 1. Number of applied shocks in the two study groups. Bi = biphasicshock waveform; Mo = monophasic shock waveform.

the two study groups with regard to all investigated clinicalparameters.

Electrical Cardioversion

Cardioversion was successful in 206 (95.4%) of 216 pa-tients. The success rate was comparable in both groups (Bi:94.3% vs Mo 96.8%; P = NS). One hundred fifty-seven pa-tients (72.7%) could be converted with the first shock intosinus rhythm. First shock efficacy showed a slight tendencytoward an advantage of the biphasic cardioversion, but thisdid reach statistical significance (Bi: 76.4% vs Mo: 67.7%;P = NS). ERAF could be documented in 19 of 216 patients;therefore, the incidence of ERAF was 8.9%. There was no dif-ference in incidence between the two study groups (Bi: 8.1%vs Mo: 9.7%, P = NS). Mean number of shocks were 1.4shocks per patient in both groups (P = NS). Most patientscould be successfully converted with one or two shocks inboth study groups (Fig. 1). The mean energy delivered wassignificantly lower in the Bi group (Bi: 186 ± 143 Ws vs Mo:324 ± 227 Ws; P < 0.001).

Discussion

Following the success of biphasic shock waveforms forinternal cardioversion, defibrillation with implantable car-dioverter defibrillators, and external defibrillation of ven-tricular fibrillation, biphasic cardioversion of AF has gainedmore attention. In this study, we investigated the influenceof biphasic versus monophasic shock waveforms on shockefficacy and the incidence of ERAF after external cardiover-sion of AF. The following results will be discussed in greaterdetail: (1) biphasic cardioversion allows comparable suc-cess rates with significantly lower energies; (2) the incidenceof ERAF is not influenced by biphasic cardioversion; and(3) with the energies used, biphasic and monophasic shockwaveforms are comparable with regard to first shock and cu-mulative shock efficacy.

In the study presented, the incidence of ERAF was 8.9%.Yu et al.7 reported an approximately 26% incidence of ERAFafter external cardioversion. A possible explanation for thedifference is the considerably longer mean duration of AF

Siaplaouras et al. Impact of Biphasic Cardioversion on ERAF and Efficacy 897

in their patients (71 ± 54 months vs 3.7 ± 8 months in ourpatients). In a previous study of our working group of pa-tients with similar clinical characteristics9 and in a study byTimmermans et al.,20 the incidence of ERAF was 12% and13%, respectively, and therefore similar to the presented data.However, in this study there was no influence of the biphasicshock waveform used on the incidence of ERAF.

In our study, the efficacy of the electrical cardioversion washigh. The two shock waveforms were comparable with regardto first shock and cumulative shock efficacy at the energiesused. In other studies reported by Ricard et al.18 and Pageet al.,17 the first shock efficacy of the biphasic cardiover-sion was higher than that of the monophasic cardioversion.In these studies, the first energy level of the monophasiccardioversion was low (100–150 Ws). In contrast to ourstudy, their studies used equal energies in both study groups(Bi/Mo). Thereafter, the cumulative efficacies of biphasic andmonophasic shocks in both studies were comparable whenthe maximum output of each defibrillator was used, as in ourstudy. Mittal et al.16 reported a superior first shock and cu-mulative shock efficacy of the biphasic cardioversion. Theydescribed a therapy protocol similar to ours. However, theircumulative success in the monophasic group was only 79%after a 360-Ws shock. Because they reported a higher efficacyof the biphasic shock only in patients with high transthoracicimpedance, one could assume that this parameter differedbetween their study group and ours.

Our results are consistent with recently published data ofScholten et al.21 and Marinsek et al.,22 who reported compa-rable first shock and cumulative shock efficacy of biphasicand monophasic cardioversion of AF using a step-up protocolsimilar to ours.

Taken together, one could suggest that biphasic cardiover-sion yields comparable first shock and cumulative shock ef-ficacy as monophasic cardioversion in terminating AF, withsignificantly lower energy delivery. Whether the lower bipha-sic energy delivery harms myocardium less than the highermonophasic energy delivery, resulting in less functional car-diac damage, is likely but requires further investigation. How-ever, neither biphasic nor monophasic external cardioversionwith the reported energies has been shown to cause structuralmyocardial damage as measured by normal serum troponinand creatinine kinase activity.18

Conclusion

Biphasic cardioversion allows comparable success rateswith significantly lower energies. However, the incidence ofERAF is not influenced by biphasic cardioversion. With theenergies used, biphasic and monophasic shock waveforms arecomparable with regard to first shock and cumulative shockefficacy.

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