Marked reduction in atrial defibrillation thresholds with repeated internal cardioversion.

Abstract OBJECTIVES This study was performed to assess the atrial defibrillation threshold in patients with recurrent atrial fibrillation (AF) using repeated internal cardioversion. BACKGROUND Previous studies in patients with chronic AF undergoing internal cardioversion have shown this method to be effective and safe. However, current energy requirements might preclude patients with longer-lasting AF from being eligible for an implantable atrial defibrillator. METHODS Internal shocks were delivered via defibrillation electrodes placed in the right atrium (cathode) and the coronary sinus (anode) or the right atrium (cathode) and the left pulmonary artery. After cardioversion, patients were orally treated with sotalol (mean 189 ± 63 mg/day). Eighty consecutive patients with chronic AF (mean duration 291 ± 237 days) underwent internal cardioversion, and sinus rhythm was restored in 74 patients. Eighteen patients underwent repeated internal cardioversion using the same electrode position and shock configuration after recurrence of AF (mean duration 34 ± 25 days). RESULTS In these 18 patients, the overall mean defibrillation threshold was 6.67 ± 3.09 J for the first cardioversion and 3.83 ± 2.62 J for the second (p = 0.003). Mean lead impedance was 55.6 ± 5.1 Ω and 57.1 ± 3.7 Ω, respectively (not significant). For sedation, 6.7 ± 2.9 mg and 3.9 ± 2.2 mg midazolam were administered intravenously (p = 0.003), and the pain score (0 = not felt, 10 = intolerable) was 5.1 ± 1.9 and 2.7 ± 1.8 (p = 0.001). Uni- and multivariate analyses revealed only the duration of AF before cardioversion to be of relevance, lasting 175 ± 113 days before the first and 34 ± 25 days before the second cardioversion in these 18 patients (p = 0.002). CONCLUSIONS If the duration of AF is reduced, a significant reduction in defibrillation energy requirements for internal cardioversion ensues. This might extend the group of patients eligible for an implantable atrial defibrillator despite relatively high initial defibrillation thresholds.