Buxton, Alfred E

Direct current cardioversion (DC CV) is an established highly effective treatment for atrial fibrillation (AF) and flutter. However, the procedure may fail to restore sinus rhythm if not performed properly. There are a number of factors that contribute to a successful outcome. Among the most prominent influences on the success of DC CV for AF is the duration of the arrhythmia; the longer the duration, the lower the chance of restoring sinus rhythm. However, although the chance of successfully restoring sinus rhythm in patients with AF of more than six months duration is statistically significantly less than that for patients with AF of lesser duration, sinus rhythm is achieved in upwards of 20% of patients with AF of long duration. 1-3 Thus, any patient with symptomatic AF should probably be given at least one cardioversion attempt to restore sinus rhythm, regardless of the duration of AF. Of note, left atrial size does not influence the ability of DC CV to restore sinus rhythm, but marked left atrial enlargement does increase the likelihood of recurrent AF.

There are a number of technical considerations that affect likelihood of successful DC CV. The arrangement of pads should ensure that the current path (between the two pads) includes as much of the fibrillating chambers as possible. This accounts for the increased success rate of an anterior-posterior pad placement, in comparison to both pads placed on the anterior chest wall (as is usual for ventricular defibrillation). Remember that the left atrium is a posterior structure. Thus, one will improve chances of successful atrial defibrillation if an anterior pad is placed over the second to third right intercostal space in tandem with a posterior pad over the inferior border of the left scapula. 4

Other factors that seem to improve success of DC CV are moderate pressure (approximately 6 pounds) on the anterior pad, and shock delivery during expiration. %6 Both have the result of decreasing transthoracic impedance.

Probably the greatest single advance improving cardioversion success has been the advent of biphasic defibrillators. just as the introduction of biphasic waveforms for ventricular defibrillation significantly improved efficacy of implanted cardioverterdefibrillators (ICDs), the use of external defibrillators having biphasic waveforms decreases the amount of energy required for cardioversion (decreasing myocardial and skin trauma), and greatly improves cardioversion success rate. 7 So great is this influence that we believe that any center performing cardioversions today should be equipped with biphasic defibrillators.

Even when biphasic shocks and the other adjunctivc measures noted previously are employed, cardioversion sometimes fails to restore sinus rhythm. In these cases, other approaches are used. One measure that can be useful is to perform cardioversion employing two defibrillators discharged simultaneously.8 If one encounters a situation where sinus rhythm is restored transiently, but AF resumes almost immediately, addition of pharmacologie antiarrhythmic agents is often useful. In such cases, administration of ibutilide or other antiarrhythmic drugs such as procainamide or flecainicle may improve success, in part, by preventing the early or immediate recurrence of AF. Ibutilide works well, but is expensive and inconvenient. Following ibutilide administration, patients must undergo continuous ECG monitoring for 4 hours in order to guard against polymorphic ventricular tachycardia (torsade de pointes). Other drugs seem to have a lower propensity to prolong the QT interval and precipitate torsade de pointes. If these measures are followed, the acute success of DC CV should be well over 90%.


1. Gallagher MM, Guo X-H, Poloniecki JD, et al. Initial energy setting, outcome and efficiency in direct current cardioversion of atrial fibrillation and flutter. J AM Coll Ca r dial 2001 ;38:1498-504.

2. Van Gelder 1C, Crijns HJ, Van Gilst WH, et al. Prediction of uneventful cardioversion and maintenance of sinus rhythm from direct-current electrical cardioversion of chronic atrial fibrillation and flutter. Am J Cardiol 1991:68:41-6.

3. Brodsky MA, Alien BJ, Capparclli KV, et al. Factors determining maintenance of sinus rhythm after chronic atrial fibrillation with left ventricular dilatation. Am] Cardiol 1989:63:1065-8.

4. Kirchhof P, Eckhart L, Loh P, et al. Anterior-posterior versus anterior-lateral electrode positions for external cardioversion of atrial fibrillation: A randomised trial. Lancet 2002;360:1275-9.

5. Deakin CD, Sado DM, Graham WP, Clcwlow F. Determining the optimal paddle force for external defibrillation. Am J Cardiol 2002;90:812-13.

6. Cohen TJ, Ibrahim B, Denier D, et al. Active compression cardioversion for refractory atrial fibrillation. Am J Cardiol 1997:80:354-5.

7. Mittal S, Shcrvin A, Stein KM, Schwartzman D, Cavlovich D,Tchou PJ, Markowitz SM, Slotwiner DJ, Scheiner MA, Lerman BB. Transthoracic cardioversion of atrial fibrillation: Comparison of rectilinear biphasic versus damped sine wave monophasic shocks. Circulation 2000;101:1282-87.

8. Saliba W, juratli N, Chung MK, et al. Higher energy synchronized external direct current cardioversion for refractory atrial fibrillation. Am J Cardiol 1999:34:2031-4.


Alfred Buxton, MD. Correspondence and affiliation previously cited.

Copyright Rhode Island Medical Society Apr 2004

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