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 repolarization (PSDR) is higher in T wave shocks that induce ventricular fibrillation (VF) than in those that do not, as well as in implantable cardioverter defibrillator (ICD) defibrillation shocks which fail to terminate VF when compared with those that are successful. BACKGROUND Ventricular fibrillation has been linked to the presence of dispersion of repolarization, which facilitates reentry. Most of the studies have been done in animals, and the mechanism underlying the generation and termination of VF in humans is speculative and remains to be determined. METHODS Monophasic action potentials (MAPs) were recorded simultaneously from the right ventricular outflow tract (RVOT) and the right ventricular apex (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 using 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 other 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 induction of VF; while following a defibrillating shock, it is associated with its failure and the continuation of VF. Conversely, a low PSDR is associated with failure of a T wave shock to induce VF and successful termination of VF by a defibrillating shock.