Journal of Interventional Cardiac Electrophysiology 9, 371–375, 2003C© 2003 Kluwer Academic Publishers. Manufactured in The Netherlands.

Internal Cardioversion of Persistent Atrial FibrillationUsing Rectilinear Biphasic Waveform

Georges H. Mairesse, Monique Raepers, IsabelleLegrand, Imad Baroud, Yvon Deheneffe, MichelEmonts, Jean-Louis Paquay and Kamal MitriCliniques du Sud-Luxembourg, Arlon, Belgium

Abstract. Internal electrical cardioversion is currentlyused in patients with persistent atrial fibrillation re-sistant to external electrical cardioversion. In exter-nal cardioversion, biphasic waveforms have shown agreater efficacy than monomorphic waveforms. Thepresent study aimed to test the safety and efficacy of rec-tilinear biphasic waveform in converting patients withpersistent atrial fibrillation to sinus rhythm using in-ternal electrical cardioversion, and to compare it withthat of classical monophasic waveform. Twenty-sevenconsecutive patients with persistent AF received 31 in-ternal cardioversions, using monophasic waveform in11 (group I), and rectilinear biphasic waveform in 20cases (group II). Baseline patients characteristics weresimilar in both groups. Multipolar catheters were posi-tioned in the distal coronary sinus and in the high rightatrium. Synchronised shocks were delivered using anescalating protocol of 2, 5, 10, 15, 20, 30, and 50 Joules. Ingroup I, 1 patient was resistant to maximal energy (suc-cess rate 91%). The mean energy of the maximal shockwas 18 ± 13 J. In group II, all patients were convertedto sinus rhythm. The mean energy of the maximal shockwas 9 ± 5 J (p< 0.01 vs. group I). No significant compli-cations occurred. At 3 months follow-up, 45% of group Iand 60% of group II patients remained in sinus rhythm(p= NS).

We conclude that internal cardioversion using rec-tilinear biphasic waveform is feasible and safe, andrequires less energy than classical monophasic wave-forms.

Key Words. atrial fibrillation, cardioversion, internalcardioversion, defibrillation

Electrical cardioversion remains the treatmentof choice to terminate persistent atrial fibrilla-tion [1]. External cardioversion has been used formore than 30 years, but success rate has neverbeen 100% [2–4]. Internal cardioversion usingelectrode catheters was proposed a few years ago,and is often effective when external cardiover-sion fails [5–14]. Biphasic waveforms are usu-ally more effective than classical monomorphicwaveforms for internal cardioversion [8–12]. How-ever, different types of biphasic waveforms areavailable.

Rectilinear biphasic waveform has been devel-oped initially for external defibrillation and takesinto account high and varied patient impedancelevel [15,16]. Unlike the biphasic truncated expo-nential waveform, the rectilinear biphasic wave-form maintains a stable shape in response toimpedance, and the constant current in the firstphase reduces potentially harmful peak currents.However, its efficacy in internal cardioversion hasnot yet been evaluated.

The present study was conducted to furtherevaluate the feasibility, safety and efficacy of rec-tilinear biphasic waveform for intracardiac car-dioversion of atrial fibrillation and to compare itwith that of classical monophasic waveform.

Methods

Patients SelectionTwenty-seven consecutive patients referred for 31internal cardioversions between may 2000 andmay 2001 were prospectively entered into thestudy. Two patients had 2 procedures for inter-nal cardioversions, and 1 patient had 3. Thesepatients were only considered reeligible for thestudy if their first internal cardioversion was suc-cessful, but had recurrent atrial fibrillation lateron. Indication for internal cardioversion was ei-ther failure of external cardioversion (n = 18),history of post-shock marked bradycardia (n = 3),presence of an implanted pacemaker (where inter-nal cardioversion was preferred to minimise therisk of pacemaker interference, n = 6), or develop-ment of atrial fibrillation during a radiofrequencyablation procedure for atrial flutter (n = 4). In

Address for correspondence: Dr. Georges H. Mairesse, MD,Cliniques du Sud-Luxembourg, Service de Cardiologie, Rue desDeportes, 137, B 6700 Arlon, Belgium. E-mail: drghmairesse@skynet.be

Received 22 October 2002; accepted 15 April 2003

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patients referred for internal cardioversion, previ-ous external cardioversion were performed usingmonophasic or biphasic energy at the discretionof the referring physician. All patients were anti-coagulated according to the standard anticoagula-tion policy in the hospital, either for >3 weeks withINR-adjusted warfarin, or with >48 hours sub-cutaneous weight-adjusted low-molecular-weightheparin in case a transoesophageal echocardio-gram showed no thrombotic formation in the leftatrium. Class III antiarrhythmic drugs were pre-scribed in all patients (except one with a previ-ous history of torsade de pointe). Amiodarone wasgiven before 27 procedures (alone, n = 15, in com-bination with class I antiarrhythmic drug, n = 6,in combination with a calcium antagonist, n = 5,in combination with a betablocker, n = 1). Sotalolwas given before 3 procedures. Propafenone withbetablocker was given in 1 case. All patients con-sented to the procedure.

Electrophysiological ProcedureThe electrophysiological study was performed un-der local anaesthesia (Lidocaine, 1%) in the fast-ing status. Three electrode catheters were insertedthrough the right femoral vein. One quadripo-lar catheter was left in the His bundle region,and could be advanced to the right ventricle incase of significant post-shock bradycardia, one10- or 20-polar commercially available deflectablecatheter (Daig) was positioned as far as possiblein the distal coronary sinus, and one catheter with75 mm-large parallel stainless steel rings (InCon-trol, Redmont, WA), specifically designed for in-ternal cardioversion, was positioned in the highright atrium. The 10 distal poles of the deflectablecatheter positioned in the coronary sinus were con-nected 〈〈all in one〉〉 and served as anode. Atrial fib-rillation was confirmed by intracardiac recording.When all catheters were in place, light sedationwas given using Midazolam (1 to 4 mg) and Pir-itramide (5 to 10 mg). The shock was synchronisedwith the external ECG and delivered 25 msec afterthe detected R-wave. An escalating protocol wasused to deliver 2, 5, 10, 15, 20, 30, and 50 Joules.The maximal energy of 50 Joules was decided ar-bitrarily, as it was presumed that application ofhigher currents internally could be harmful to thepatients. The defibrillation threshold was definedby the lowest demanded energy delivered to obtaincardioversion. When cardioversion was obtained,atrial fibrillation was not reinduced and no furthershocks were delivered.

Shock WaveformsThe first 11 procedures were performed using con-ventional damped sine wave monomorphic wave-

Fig. 1. Waveform morphology: Comparison of damped sinemonophasic waveform (in dotted line), and rectilinearbiphasic waveform (in black line).

forms (Group I patients). These were generatedby a Zoll M Series monophasic defibrillator (ZollMedical Corporation, Burlington, Mass), whichdelivered the stored charge on a 45 µF capacitorthrough a 20 MHz inductor and an internal resis-tance of 14 �.

The last 20 procedures were performed us-ing rectilinear biphasic waveforms (Group II pa-tients). These were generated by a Zoll M Seriesbiphasic defibrillator (Zoll Medical Corporation,Burlington, Mass), from a 100 µF capacitor. Therectilinear biphasic waveform consisted of a con-stant current 6 msec first phase, followed by atruncated exponential 4 msec phase (Fig. 1). Theconstant current first phase was produced by au-tomatically adjusting the internal resistance ofthe defibrillator circuit on the basis of the pa-tient’s internal impedance, which was automati-cally determined at the onset of the shock delivery[15,16].

In both cases, the electrode catheters were con-nected to the defibrillator using custom madeadaptators with no internal resistance.

Follow-up and Statistical AnalysisPatients were discharged from the hospital 1 dayafter the procedure. In the absence of contra-indications, patients were left on Amiodarone200 mg per day. Anticoagulation was prescribedat least for 1 month. Follow-up information wasobtained from the patient in the outpatient clinic3 months after the procedure unless earlier recur-rence was documented.

Data are expressed as mean ± 1 standard de-viation and were compared using the Studentt-test for unpaired data. A p-value of 0.05 wasconsidered indicative of statistically significantdifference.

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Table 1. Patients characteristics

Group I Group IIMonophasic Biphasic(N = 11) (N = 20)

Sex ratio 7/10 males 11/18 malesAge 73 ± 6 y 71 ± 6 yStructural heart disease 9/11 (82%) 15/20 (75%)Left ventricular ejection fraction 60 ± 6% 59 ± 9%Left atrial diameter 51 ± 7 mm 54 ± 8 mmPrevious shocks 1.6 ± 0.7 2 ± 1Previous antiarrhythmic drugs 2 ± 0.7 2.1 ± 0.8

Results

Patients CharacteristicsThe patient population consisted of 17 men and10 women. Mean age was 72 ± 6 years. Structuralheart disease was present in 22 patients (81%).Hypertension was present in 8 patients, coronaryartery disease in 6 patients, valvular disease in4 patients, and dilated cardiomyopathy in 4 pa-tients. Five patients had lone atrial fibrillation. Allthese patients had a long previous history of atrialfibrillation. They had already experienced 1 to 8previous shocks (mean 1.9 ± 0.9), and 1 to 5 previ-ous antiarrhythmic drugs (mean 2.1 ± 0.8). Meanleft atrial size measured by echocardiogram in theparasternal long axis view was 53 ± 8 mm, andmean ejection fraction assessed by bidimentionalechocardiography was 59 ± 7%. There was no sig-nificant difference in patient’s characteristics be-tween group I and group II patients (Table 1).Both groups were also comparable in terms of drugregimen.

CardioversionResults are presented in Figure 2. In group I,using monophasic shocks, one patient failed tobe cardioverted even at the maximal energy of50 Joules (success rate 91%). The mean defibril-lation threshold was 18 ± 10 Joules. In group II,using rectilinear biphasic shocks, all patients werecardioverted with a maximum of 20 Joules (suc-cess rate 100%, p = NS vs. monophasic). Themean defibrillation threshold was 9 ± 5 Joules(p < 0.01 vs. monophasic). Impedance measuredduring the successful shock was similar in bothgroups: 74 ± 17 Ohm with monophasic shock vs.75 ± 16 Ohm with rectilinear biphasic shocks (p =NS). In the 3 patients with repeated internal car-dioversion, the successful energy was in the firstpatient: 5 Joules biphasic and 2 Joules biphasic, inthe second patient: 5 Joules biphasic and 5 Joulesbiphasic, and in the third patient: 10 Joulesmonophasic, 30 Joules monophasic, and 10 Joulesbiphasic.

Fig. 2. Cardioversion data: Successfull energy (Joules) toachieve cardioversion. Values are expressed as percentage ofeach group.

Follow-upNo significant complications occurred after theprocedure. Four patients presented mild groinhaematoma at the level of femoral vein puncture,but no specific intervention was needed. Four pa-tients (1 of group I and 3 of group II, 13%) hadearly recurrence of atrial fibrillation before leav-ing the cath lab. At 3 months, 5 of 11 patients fromgroup I (45%), and 12 of 20 patients of group II(60%) remained in sinus rhythm (p = NS). In thissmall series, no clinical or echocardiographic pa-rameter was found to be predictive of early or laterecurrence of atrial fibrillation.

Discussion

The present study shows that rectilinear biphasicshocks are more effective than monophasic shocksfor successful internal cardioversion of persistentatrial fibrillation. Rectilinear biphasic shocks re-quire significantly less energy than monophasicshocks.

Successful defibrillation depends on the defib-rillator’s ability to generate sufficient current flowthrough the heart [3]. Defibrillation current has2 components: First, average current delivery isa key determinant of successful defibrillation andis directly influenced by the patient’s impedance.Secondly, high peak currents are associated withmyocardial injury.

Biphasic defibrillation technology was firstused in implantable cardioverter defibrillators.The characteristic of biphasic shocks is to be de-livered in 2 directions. During the first phase,the current moves from the anode to the cath-ode as during monophasic shocks. During thesecond phase, the current flow reverses direc-tion. The underlying mechanisms are not fully

374 Mairesse et al.

understood yet, but it is clear that biphasic waveform lowers the electrical threshold for success-ful defibrillation. During external cardioversion,the benefits for the patients of biphasic technol-ogy also include less myocardial dysfunction af-ter defibrillation [17] and a lower risk of skinburns.

Conversely to biphasic truncated exponen-tial waveform which was initially developedfor internal use, rectilinear biphasic waveformshave been developed primarily for external car-dioversion to take into account high and variedpatient impedance levels. During external car-dioversion with biphasic truncated exponentialwaveforms, variations in impedance have beenshown to modify the waveform’s shape, and there-fore its efficacy. The rectilinear waveform main-tains a stable shape in response to impedance,and the constant current in the first phasereduces even further potentially harmful peakcurrents.

Although less important than during externalcardioversion, impedance may also vary from onepatient to another and from one catheter posi-tion to another during internal cardioversion. Thismay be associated with varying efficacy. On theother hand, high peak currents delivered at theimmediate vicinity of the endothelium can theo-retically produce potentially harmful internal le-sions [17]. It seems thus reasonable to make everyeffort to reduce energy delivery and peak currents.In the present study, we successfully cardiovertedall patients with very low energies and did not de-plore any complications.

In comparison with previous studies [7–12],the reported efficacy of intracardiac shocks variesfrom 70 to 100% for the successful cardioversion ofpersistent atrial fibrillation. Defibrillation thresh-old varies from 1.2 to 19 Joules according to pa-tient’s selection, leads and device selection. Thepresent results are concordant with these find-ings. In this patient’s population, more than halfof the patients were included because of failure ofrepeated external cardioversion with 360 Joules.This may also suggest a patient’s population withslightly higher energy requirements.

In the present study, early recurrence of atrialfibrillation was observed in 4 patients (13%),which is also exactly concordant with what is re-ported in the literature [18]. Rectilinear biphasicwaveform did not had any influence on this phe-nomenon.

The small number of patients in the presentstudy could be considered as a potential limita-tion. However, the patients were consecutive pa-tients with no selection bias. The majority of thesepatients were selected after failure of external car-dioversion using monophasic or biphasic energy

at the discretion of the referring physician. Themajority of these external cardioversions wereperformed using monophasic shocks, which mayrepresent a selection bias. However, a correlationbetween failure or success of monophasic or bipha-sic energy between external and internal shockshave never been reported. Furthermore, this studyonly compared the efficacy of internal cardiover-sion using rectilinear biphasic shocks to classicalmonophasic shocks. To our knowledge, even for ex-ternal defibrillation, no study exists today compar-ing the 2 biphasic morphologies. Further studiesshould certainly focus on this aspect.

We conclude that internal cardioversion usingrectilinear biphasic waveform is feasible and safe,and requires less energy than classical monopha-sic waveforms. Decreased current requirementwith decreased high peak currents suggest thatrectilinear biphasic shocks may be the preferredmethod for internal electrical cardioversion of per-sistent atrial fibrillation.

References

1. Furster V, Ryden LE, Asinger RW, et al. ACC/AHA/ESCGuidelines for the management of patients with atrial fib-rillation: Executive summary. Circulation 2001;104:2118–2150.

2. Lown B, Perloth MG, Kaidbe S, Abe T, Harken DW. «Car-dioversion» of atrial fibrillation: A report on the treatmentof 65 episodes in 50 patients. N Engl J Med 1963;269:325–331.

3. Dell’Orfano JT, Nacarelli GV. Update on externalcardioversion and defibrillation. Curr Opin Cardiol2001;16:54–57.

4. Ricard P, Levy S, Boccara G, Lakhal E, Bardy G. Exter-nal cardioversion of atrial fibrillation: comparison of bipha-sic vs. monophasic waveform shocks. Europace 2001;3:96–99.

5. Levy S, Lauribe P, Dolla E, et al. A randomized compari-son of external and internal cardioversion of chronic atrialfibrillation. Circulation 1992;86:1415–1420.

6. Levy S, Ricard P, Lau CP, et al. Multicenter low–energytransvenous atrial defibrillation trial results in differ-ent subsets of atrial fibrillation. J Am Coll Cardiol1997;29:750–755.

7. Sopher SM, Murgatroyd FD, Slade AKB, et al. Low en-ergy internal cardioversion of atrial fibrillation resistantto transthoracic shocks. Heart 1996;75:635–638.

8. Schmitt C, Alt E, Plewan A, et al. Low energy intracardiaccardioversion after failed conventional external cardiover-sion of atrial fibrillation. J Am Coll Cardiol 1996;28:994–999.

9. Neri R, Palermo P, Cesario AS, Baragli D, Amici E,Gambelli G. Internal cardioversion of chronic atrial fib-rillation in patients. PACE 1997;20:2237–2242.

10. Blommaert D, De Roy L, Adam JF, Jamart J, MucimbitsiJ. Limited internal shocks for atrial fibrillation refrac-tory to external cardioversion. International Journal ofCardiology 1999;71:71–78.

Biphasic Waveform for Internal Cardioversion 375

11. Taramasco V, Socas A, Ricard P, Levy S. Internal low–energy cardioversion: A therapeutic option for restoringsinus rhytm in chronic atrial fibrillation after failure ofexternal cardioversion. Europace 1999;1:179–182.

12. Boriani G, Biffi M, Camanini C, Luceri RM, Branzi A.Transvenous low energy internal cardioversion for atrialfibrillation. PACE 2001;24:99–107.

13. Andraghetti A, Scalese M. Safety and efficacy of low-energy cardioversion of 500 patients using two differenttechniques. Europace 2001;3:4–9.

14. Paravolidakis KE, Kolettis TM, Theodorakis GN,Paraskevaidis IA, Apostolou TS, Kremastinos DTh.Prospective randomized trial of external versus internaltranscatheter cardioversion in patients with chronicatrial fibrillation. J Interventional Cardiac Electrophysiol1998;2:249–253.

15. Mittal S, Ayati S, Stein KM. Comparison of a novel recti-linear biphasic waveform with a damped sine monomor-phic waveform for transthoracic ventricular defibrillation.J Am Coll Cardiol 1999;34:1595–1601.

16. Mittal S, Ayati S, Stein KM. Transthoracic cardioversionof atrial fibrillation. Comparison of rectilinear biphasicversus damped sine wave monophasic shocks. Circulation2000;101:1282–1287.

17. Tang W, Weil MH, Sun S, et al. The effects of biphasicand conventional monophasic defibrillation on postresus-citation myocardial function. J Am Coll Cardiol 1999;34:815–822.

18. Timmerman C, Rodriguez LM, Smeets JLRM, WellensHJJ. Immediate reinitiation of atrial fibrillation followinginternal atrial defibrillation. J Cardiovasc Electrophysiol1998;9:122–128.