Marked reduction in atrial defibrillation thresholds with repeated internal cardioversion

OBJECTIVES This study was performed to assess the atrial defibrillation thr eshold in patients with recurrent atrial fibrillation (AF) using repeated i nternal cardioversion. BACKGROUND Previous studies in patients with chronic AF undergoing internal cardioversion have shown this method to be effective and safe. However, cu rrent energy requirements might preclude patients with longer-lasting AF fr om 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, patien ts were orally treated with sotalol (mean 189 +/- 63 mg/day). Eighty consec utive patients with chronic AF (mean duration 291 +/- 237 days) underwent i nternal cardioversion, and sinus rhythm was restored in 74 patients. Eighte en patients underwent repealed internal cardioversion using the same electr ode position and shock configuration after recurrence of AF (mean duration 34 +/- 25 days). RESULTS In these 18 patients, the overall mean defibrillation threshold nas 6.67 +/- 3.09 J for the first cardioversion and 3.83 +/- 2.62 J for the se cond (p = 0.003). Mean lead impedance was 55.6 +/- 5.1 Omega and 57.1 +/- 3 .7 Omega, respectively (not significant). For sedation, 6.7 +/- 2.9 mg and 3.9 +/- 2.2 mg midazolam were administered intravenously (p = 0.003), and t he 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 bef ore the first and 34 +/- 25 days before the second cardioversion in these 1 8 patients (p = 0.002). CONCLUSION If the duration of AF is reduced, a significant reduction in def ibrillation energy requirements for internal cardioversion ensues. This mig ht extend the group of patients eligible for an implantable atrial defibril lator despite relatively high initial defibrillation thresholds. (C) 1999 b y the American College of Cardiology.