High dispersion of ventricular repolarization after an implantable defibrillator shock predicts induction of ventricular fibrillation as well as unsuccessful defibrillation

OBJECTIVES To test the hypothesis that post-shock dispersion of repolarizat ion (PSDR) is higher in T wave shocks that induce ventricular fibrillation (VF) than in those that do not, as well as in implantable cardioverter defi brillator (ICD) defibrillation shocks which fail to terminate VF when compa red with those that are successful. BACKGROUND Ventricular fibrillation has been Linked to the presence of disp ersion of repolarization, which facilitates reentry. Most of the studies ha ve been done in animals, and the mechanism underlying the generation and te rmination of VF in humans is speculative and remains to be determined. METHODS Monophasic action potentials (MAPs) were recorded simultaneously fr om the right ventricular outflow tract (RVOT) and the right ventricular ape x (RVA) in 27 patients who underwent implantation and testing of an ICD. T wave shocks were used to induce VF while the termination was attempted usin g internal defibrillator shocks. The post-shock repolarization time (PSRT) was measured in both the RVA and RVOT MAPs, and the difference between the two recordings was defined as the PSDR. The averages of PSDR were compared between the successful and unsuccessful inductions and terminations of VF. RESULTS T wave shocks that induced VF generated a greater PSDR (93.4 +/- 85 .1 ms) than the unsuccessful ones (45.1 +/- 55.9 ms, p < 0.001). On the oth er hand, shocks that failed to terminate VF were associated with a greater PSDR (59.9 +/- 41.2 ms) than shocks that terminated VF (21.1 +/- 20.1 ms), p < 0.001. CONCLUSIONS A high PSDR following a T wave shock is associated with inducti on of VF; while following a defibrillating shock, it is associated with its failure and the continuation of VF. Conversely, a low PSDR is associated w ith failure of a T wave shock to induce VF and successful termination of VF by a defibrillating shock. (J Am Coil Cardiol 2000;35:422-7) (C) 2000 by t he American College of Cardiology.