927-35 Internal Atrial Defibrillation: Need for Concomitant Pacemaker Therapy and Its Effect on Pacemaker Function

Abstract

Implantable defibrillators are being considered as a therapeutic option for the chronic management of atrial fibrillation (AF). The need for concomitant pacemaker therapy and the effect on existing pacemaker function of internal atrial defibrillation (lAD) shocks is unknown. 21 pts, mean age 67 ± 11 yrs, mean LA diameter 43 ± 7 mm, mean LV ejection fraction 36.5 ± 15%, underwent lAD for drug refractory AI’ 7 pts had existing WIR pacemakers. Lead configurations tested for lAD using a step up protocol were RV-RA, RV-SVC, RV-axillary patch, RA-Ieft pulmonary artery (LPA) or RA-coronary sinus (CS). RA-LPA or CS were preferred for pts with pacemakers. Of 178 biphasic shocks delivered with energies of 1 to 20 J, 36 were successful in cardioverting AF and these were analyzed. R-R interval preceding the successful shock ranged from 200 to 1000 ms. Mean time to the first post shock QRS was 1076 ± 368 ms (vs mean proshock R-R interval of 780 ± 18 ms, p = 0.005) and the mean first sinus cycle length of 168 ± 490 ms (vs 780 ± 18 ms preshock R-R interval. p < 0.005). Significant post shock bradycardias occurred in 6 pts (28%), 1 pt had sinus arrest with third degree AV block lasting for 7.5 s. 2 pts had third degree AV block requiring ventricular pacing support. 3 pts had post shock pauses >2 s with 1 pt having a persistent sinus cycle of 2.5 s for 6 s. There was no correlation between energy used, lead configurations and the incidence of bradycardias. The 7 pts with existing WIR pacemakers were successfully cardioverted using the RA-LPA or CS configuration at a mean energy of 9.81 ± 8.6 J. There was no effect of lAD using the RA-LPA or CS configuration on pacemaker function. 1. Pts undergoing lAD may have a transient bradycardia following successful cardioversion which may require backup concomitant ventricular pacing. 2. lAD can be performed safely in pts with existing pacemakers using RA-LPA or CS lead configurations without affecting pacemaker function at the energy levels tested. 3. An implantable atrial defibrillator should incorporate concomitant ventricular pacing support.