Clinical efficacy and safety of atrial defibrillation using biphasic shocks and current nonthoracotomy endocardial lead configurations

We undertook a prospective randomized clinical trial evaluating efficacy and safety of internal atrial defibrillation in patients with drug-refractory atrial fibrillation (AF). Consecutive patients with paroxysmal or chronic AF were randomly tested with 3 internal atrial defibrillation lead configurations and biphasic shocks. Patients with implanted cardiac pacemakers were tested with the right atrium (RA) and left pulmonary artery or coronary sinus (CS) configuration. Shocks were initially delivered without anesthesia to assess parient tolerance. The need for backup ventricular defibrillation and pacing support was evaluated. Eighteen patients with (n = 15) or without (n = 3) structural heart disease, mean left ventricular ejection fraction 36 ± 14%, and mean left atrial diameter 4.5 ± 0.6 cm were studied. The mean defibrillation threshold in the best randomized lead configuration was 9.9 ± 7.7 J. Mean defibrillation threshold for the right ventricle (RV) and superior vena cava configuration was 13.3 ± 5 J, which was significantly lower than the RA and axilla configuration (20.1 ± 7.4 J, p < 0.04) but not the RV to RA configuration (16.5 ± 11 J, p > 0.2). The mean defibrillation threshold using the RA-left pulmonary artery/ CS configuration was 8.9 ± 9 J (p > 0.2 vs RV-superior vena cava). There was a bimoaal distribution of defibrillation thresholds. Low atrial defibrillation thresholds correlated with absence of heart disease, higher ejection fraction, and smaller left ventricular end-diastolic diameter. Shocks were hemodynamically well tolerated, but 18 patients (11%) had nonsustained ventricular tachycardia after shock delivery. Eighteen patients (33%) had postshock brad/arrhythmias. Fourteen of 16 patients perceived shocks ≥3 J as intolerable. We conclude that internal atrial defibrillation is clinically effective at energies ≤20 J using existing nonthoracotomy lead systems. Specific lead configurations may achieve lower defibrillation thresholds. Shocks are hemodynamically well tolerated but can induce bradyarrhythmias ana ventricular arrhythmias. Backup ventricular pacing and defibrillation are desirable. Patient tolerance for shocks >2 J is limited. Thus, this technique is applicable for infrequent application. Adjunctive therapy will be needed in patients with frequent or drugrefractory AF.