Socas et al.Transvenous cardioversion of atrial fibrillation

Transvenous Cardioversion of Atrial Fibrillationusing Low-Energy Shocks

Ariel G. Socas, Philippe Ricard, VincentTaramasco, Maxime Guenoun, and Samuel LévyUniversity of Marseille, School of Medicine, CardiologyDivision, Hôpital Nord, Marseille, France

Abstract. Recent reports have suggested that transvenous

cardioversion of atrial fibrillation is feasible using low-en-

ergy shocks and a right atrium coronary sinus electrode

configuration. We evaluated in a prospective study the effi-

cacy and safety of low-energy internal cardioversion of

atrial fibrillation in 104 consecutive patients. Sixty-two

patients presented with chronic atrial fibrillation (group I),

16 had paroxysmal atrial fibrillation (group II), and 26 had

an induced atrial fibrillation episode (group III). The mean

duration of the presenting episode of atrial fibrillation was

9 6 19 months for group I, 4 6 2 days for group II, and 18

6 7 minutes for group III. Atrial defibrillation was per-

formed using two intracardiac catheters: one was placed in

the right atrium (cathode) and the other in the coronary

sinus or in the left branch of the pulmonary artery (anode).

The catheters were connected to a customized external

defibrillator capable of delivering 3/3-ms biphasic waveform

shocks with a voltage programmable between 10 and 400

volts. The shocks were synchronized to the R wave. Sinus

rhythm was restored in 44 of the 62 patients in group I

(70%), in 12 of the 16 patients in group II (75%), and in 20

of 26 patients in group III (77%). The mean voltage and

energy required for cardioversion were respectively 300 6

68 V and 3.5 6 1.5 J, for group I, 245 6 72 V and 2.0 6 0.9 J

for group II, and 270 6 67 V and 2.6 6 1.2 J for group III.

The leading-edge voltage required for sinus rhythm restora-

tion was significantly higher (p , 0.05) in the chronic atrial

fibrillation group than in the paroxysmal or induced groups.

No proarrhythmic effects ocurred for the delivered 686

R-wave synchronized shocks. This study of a large group of

patients confirms and extends the results of previous re-

ports. Such findings may have clinical implications for elec-

tive cardioversion of atrial fibrillation and the development

of an implantable atrial defibrillator.

Key words. Atrial fibrillation, internal cardioversion, low-

energy cardioversion

Restoration of sinus rhythm is a primary therapeuticendpoint for patients with non-self-terminating atrialfibrillation. This therapeutic strategy offers severalbenefits e.g., to eliminate symptoms when atrial fibrilla-tion is symptomatic and to decrease embolic risk andhemodynamic complications. External electricalcardioversion is the technique currently used for restor-ing sinus rhythm electively in non-self-terminatingatrial fibrillation [1]. Lévy et al. [2] reported a technique

for high-energy internal cardioversion using a 200-J mo-nophasic shock delivered between the proximal elec-trode of a catheter placed in the right atrium and a blackplate. Its efficacy was shown to be superior to externalcardioversion [3,4]. Both external and high-energy in-ternal cardioversion require general anesthesia.

In 1993, using a sheep model of atrial fibrillation,Cooper et al. reported [5] that low-energy ( , 5 J) in-ternal atrial defibrillation was feasible and that thebest electrode configuration included right atrial andcoronary sinus catheters. Preliminary reports in hu-mans [6,7] investigated this technique mainly in atrialfibrillation induced in the electrophysiology laboratory.These studies showed that restoration of sinus rhythmusing low-energy shocks was possible, under sedation,in the majority of patients The aim of the present arti-cle is to report our experience with this technique in alarge series of patients.

Methods

From March 28, 1994, to July 18, 1996, 104 patientswith non self-terminating atrial fibrillation in whomcardioversion was indicated entered this prospectivestudy, the aim of which was to evaluate the efficacy andsafety of low-energy cardioversion. This study was ap-proved by the Ethical Committee of the University ofMarseille. Written informed consent was obtainedfrom each patient before the procedure.

Atrial fibrillation was defined as chronic when it waspresent for 7 days or longer. Paroxysmal atrial fibrilla-tion was defined as recurrent attacks of arrhythmialasting less than 7 days. The involuntary occurrence ofan atrial fibrillation episode during the course of theelectrophysiologic exploration, either by mechanicalcontact or during programmed atrial stimulation, wasconsidered to be induced atrial fibrillation. The pres-ence of an antiarrhythmic treatment at the time of

Journal of Interventional Cardiac Electrophysiology 1997;1:125–129

© Kluwer Academic Publishers. Boston. Printed in U.S.A.

125

Address for correspondence: Samuel Lévy MD, University ofMarseille, School of Medicine, Cardiology Division, Hôpital Nord,13015 Marseille, France.

Received 28 January 1997; accepted 28 January 1997

area was 1.86 6 0.21 m2 (range 1.38–2.34). Structuralheart disease was detected in 52 patients (Table 1).Twenty-six patients had valvular heart disease, includ-ing mitral regurgitation in nine patients, mitralstenosis in three patients, combined stenosis and re-gurgitation in three patients, aortic stenosis in onepatient, aortic regurgitation in one patient, mitral andaortic regurgitation in four patients, aortic stenosisand mitral regurgitation in one patient, mitral valvereplacement in two patients, aortic valve replacementin two patients, and both aortic and mitral valve re-placement in two patients. Hypertension was presentin 18 patients, dilated cardiomyopathy in three pa-tients, hypertrophic cardiomyopathy in two patients,hemochromatosis in one patient, and atrial septal de-fect in two patients. In 52 patients, atrial fibrillationwas idiopathic. Patients were subdivided into threegroups: chronic atrial fibrillation (group I), paroxysmalatrial fibrillation (group II), and induced atrial fibrilla-tion (group III). The clinical characteristics of thesethree groups of patients did not show any statisticaldifference (Table 1). Sinus rhythm was restored usinglow-energy internal cardioversion in 76 patients (73%).The remaining 28 patients (27%) completed the proto-col, but the procedure failed to restore sinus rhythm.Mean impedance and RR interval of the last shockdelivered were 62 6 1 ohms and 679 6 162 ms, respec-tively. Data concerning success rates, mean voltage,and energy requirements are shown in Table 2. Successrates were not significantly different among the threegroups of patients.

Of interest, the mean voltage and energy requiredto restore sinus rhythm were significantly lower in theparoxysmal and induced atrial fibrillation groups thanin the chronic atrial fibrillation group (p , 0.05). Thecoronary sinus could not be catheterized in 23 patients,and therefore the catheter was positioned in the leftbranch of the pulmonary artery. The mean successfulenergy was 3.6 6 1.5 J when the catheter was placed inthe pulmonary artery and 2.9 6 1.4 J when it wasplaced in the coronary sinus. Success rates were 73%and 71%, respectively. An example of restoration ofsinus rhythm using this technique is shown in figure 2.

There was no relation between the success or failureof the procedure and each of the following clinical vari-

ables: age, sex, weight, body surface area, and leftatrial size. For group I (chronic atrial fibrillation), theduration of the presenting episode of atrial fibrillationwas significantly shorter for the successful proceduresthan for failures, with a mean duration of 168 6 372 and536 6 783 days, respectively (p , 0.05).

A total number of 686 shocks were delivered to the104 patients. No complications occurred with correctlysynchronized shocks.

The data concerning shock-related pain have beenreported elsewhere [5].

Discussion

The present study confirms the feasibility, efficacy, andsafety of low-energy transvenous cardioversion ofatrial fibrillation using biphasic shocks and rightatrium coronary sinus electrode configuration [7–11].Keane et al. [17] reported a successful procedure in 8of 9 patients, with a mean energy of 6.7 6 2 J. Johnsonet al. [8] were able to defibrillate six patients withinduced atrial fibrillation, using a mean energy of 2.5 61.4 J. Alt et al. [10] reported their initial experience onchronic atrial fibrillation, and were successful in 10 of13 patients, with a mean energy of 3.7 6 1.7 J. In aseries of 19 patients, Murgatroyd et al. [11] reported asuccess rate of 100%, with a mean leading voltage of237 6 55 V and a mean energy of 2.16 6 1.02 J (range0.7 6 4.4 J). In their series, 15 of 19 patients had atrialfibrillation induced at the electrophysiology labora-tory. The present report represents the largest series,from a single center, of patients with atrial fibrillationwho were treated with this technique. The other largeseries that has been reported was a multicenter trial[19]. In this series, the success rate of the techniquewas 73%. There was no significant difference in successrates among the three groups (chronic, paroxysmal,and induced). However, the leading-edge voltage of thesuccessful shock was significantly lower in patientswith paroxysmal atrial fibrillation than in patients withchronic atrial fibrillation. Our results are in keepingwith those of the Multicenter XAD Trial [9]. No ven-tricular proarrhythmia was observed with R-wavesynchronized shocks in our series, nor in the Multicen-ter Trial. A ventricular tachycardia episode degenerat-

Table 2. Success rate, mean voltage, and energy of successful shocks for the three groups of patients

Success Voltage EnergyType of AF No. of Pts. (%) (No. of Pts. %) (V) (J)

Chronic 62 44 (70%) 300 6 68 3.5 6 1.5A

(Group I)Paroxysmal 16 12 (75%) 245 6 72 2.0 6 0.9A

(Group II)Induced 26 20 (77%) 270 6 67 2.6 6 1.2A

(Group III)

A p , 0.05.

128 Socas et al.

ing into ventricular fibrillation was induced with a non-synchronized shock in a patient with atrial flutter. Thispatient was not included in this series because thearrhythmia treated was not atrial fibrillation and be-cause the RR interval preceding shock delivery wasprogrammed at 400 ms. This potential complicationemphasizes the importance of proper R-wave synchro-nization. In an animal study, Ayers et al. [11] reportedthat when the RR interval preceding the shock wasless than 300 ms, a ventricular proarrhythmic risk ex-isted even if the shock was R-wave synchronized. Inthis study, the minimum RR interval preceding theshock was programmed at 500 ms or more.

Shock-related pain is an important issue of atrialdefibrillation. This aspect was dealt with in anotherstudy, which showed that there is a relationship be-tween the energy delivered and patient discomfort [5].However, an important interindividual variability didexist.

Low-energy internal cardioversion has severalclinical implications. Atrial defibrillation without theneed of general anesthesia allows the researcher tocomplete an electrophysiologic study in case of an in-voluntary episode of atrial fibrillation. Transvenouslow-energy, cardioversion may be useful, particularlywhen external cardioversion fails. This technique couldbe of interest in the treatment of patients with chroniclung disease since it avoids general anesthesia, whichis high risk in these patients. Data concerning, low-en-ergy internal cardioversion support the concept of animplantable atrial defibrillator [13].

Conclusions

This study shows that low-energy transvenouscardioversion, to restore sinus rhythm in patients withatrial fibrillation, is feasible. The energy levels re-quired to restore sinus rhythm are lower in patientspresenting with induced or paroxysmal atrial fibrilla-tion than in patients with chronic atrial fibrillation.This technique may be useful to terminate involuntar-ily induced atrial fibrillation that complicates routineelectrophysiologic studies or radiofrequency ablationprocedures. Finally, this study shows the feasibility oflow-energy internal cardioversion in a large cohort of

consecutive patients and supports the concept of anatrial implantable defibrillator [11].

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