Relation of the intraoperative defibrillation threshold to successful postoperative defibrillation with an automatic implantable cardioverter defibrillator

Abstract

To determine the relation between the intraoperative defibrillation threshold and successful postoperative termination of induced ventricular fibrillation (VF) with the automatic implantable cardioverter defibrillator (AICD), 33 patients who underwent AICD implantation were studied. The defibrillation threshold, determined after at least 10 seconds of VF, was 5 J in 2, 10 J in 6, 15 J in 10, 20 J in 10 and 25 J in 5 patients. The AICD energy rating on the first discharge was 28 ± 1.8 J. Defibrillation of induced VF was demonstrated postoperatively in 29 of 33 (88%) patients. The AICD terminated VF postoperatively in all 18 patients with a defibrillation threshold ≤ 15 J. Only 11 of the 15 (73%) patients with a defibrillation threshold ≥ 20 J (p < 0.04) had VF terminated postoperatively. In all 4 patients in whom the AICD failed to terminate induced VF, the energy difference between the AICD rating and the defibrillation threshold was ≤ 10 J. Among the 14 patients with a difference of ≤ 10 J between the AICD energy rating and the defibrillation threshold, there were no significant differences between the 4 patients with and the 10 without successful VF termination with respect to the duration of VF induced postoperatively or the AICD lead system. In summary, failure to terminate VF with the AICD is not uncommon (27%) when the defibrillation threshold approaches the energy delivering capacity of the AICD. A margin of >10 J between the AICD energy rating and the defibrillation threshold should be sought by modifying lead type, size and position or by selecting the appropriate energy rating of the AICD device.