ATRIAL FIBRILLATION FLUTTER INDUCED BY IMPLANTABLE VENTRICULAR DEFIBRILLATOR SHOCKS - DIFFERENCE BETWEEN EPICARDIAL AND ENDOCARDIAL ENERGY DELIVERY/

Atrial Fibrillation/Flutter Induced by Defibrillator Shocks, Introduct ion: We evaluated the incidence and energy dependence of atrial fibril lation/flutter (AF) induced by implantable ventricular defibrillator s hocks in 63 patients tested in the operating room or electrophysiology laboratory. Methods and Results: Defibrillator shocks were epicardial monophasic in 32 patients, and through an Endotak(R) lead endocardial monophasic in 19 and biphasic in 12 patients. The epicardial and endo cardial patient groups had similar clinical characteristics. A total o f 517 defibrillator shocks were given. The epicardial group received 3 36 total defibrillator shocks and 10 +/- 6 shocks (mean +/- SD) per pa tient compared with the endocardial group, which received 181 total sh ocks and 6 +/- 4 defibrillator shocks per patient (P = 0.004). In the epicardial group, AF occurred in 13 (41%) patients and in 17 (5%) of t he 336 shocks. No AF was induced with endocardial defibrillator shocks . The epicardial mean energy was 16 +/- 9 J, lower than the endocardia l mean energy of 20 +/- 9 J (P < 0.004). In the epicardial monophasic group, energy correlated with AF induction, Each patient received 7 +/ - 6 defibrillator shocks < 15 J and 4 +/- 2 shocks greater than or equ al to 15 J, yet AF occurred in only 2.3% versus 9.6% (P < 0.05) of def ibrillator shocks < 15 J and greater than or equal to 15 J, respective ly. Of note, AF was not induced with energy < 4 J or > 31 J. Conclusio ns: In the epicardial configuration, AF induction is energy dependent, with an apparent lower and upper limit of vulnerability. AF induction by defibrillator shocks delivered through an Endotak lead is very rar e, possibly related to an apparent upper limit of vulnerability of les s energy, avoidance of thoracotomy, or different energy field distribu tion.