Uncorrected atrial fibrillation is a common cause of morbidity and mortality because of impaired hemodynamic function, uncontrolled ventricular rate, and increased risk of stroke. External cardioversion is the accepted method of restoring sinus rhythm, but it is frequently unsuccessful. It has been suggested that anteroposterior positioning of the paddles improves success rates because the position delivers a more efficient shock to both atria, and transthoracic impedance is reduced. Studies, however, have found variable success rates with anteroposterior and anterolateral placement of paddles. Kirchhof and colleagues compared the two positions in a study of more than 100 consecutive patients with persistent atrial fibrillation suitable for cardioversion.
The patients were referred to a German university center for cardioversion because of atrial fibrillation. Patients with pacemakers, atrial flutter, or rapid tachycardias were excluded from the study group. Electrocardiograms were checked on all patients on the day before the cardioversion. The patients were randomly assigned to undergo cardioversion with anteroposterior or anterolateral placement of paddles. In other respects, cardioversion was performed using the same technique on all patients. If the initial attempt at 50 joules was unsuccessful, the protocol proceeded in a stepwise manner up to 360 joules. If cardioversion was still unsuccessful, the paddle position was changed, and cardioversion was again attempted at 360 joules.
Although initially planned for 100 patients per group, the study was terminated after 108 patients had been treated because of evidence of benefit in the anteroposterior position group. Of the first 50 patients treated with paddles in this position, 49 were successfully converted compared with only 39 of the first 50 treated in the anterolateral position. In the final analysis, 50 of 52 patients (96 percent) treated with anteroposterior paddle positioning were cardioverted compared with 44 of 56 patients (78 percent) using the anterolateral position. For patients failing the original treatment, eight of the 12 changing from anterolateral to anteroposterior were successful, but none of those switching from the other direction were successfully cardioverted. In logistic regression analysis of multiple factors associated with successful cardioversion, only anteroposterior positioning of the paddles and low body mass index independently predicted success.
The authors conclude that anteroposterior positioning of electrodes is more effective than anterolateral positioning in external cardioversion of persistent atrial fibrillation. They believe this finding can be explained by anatomic features that result in a more efficient shock wave.