Early recurrence of ventricular fibrillation after successful defibrillation during prolonged global ischemia in isolated rabbit hearts.

INTRODUCTION: The mechanisms that lower the efficacy of electrical defibrillation during prolonged global ischemia remain unclear. METHODS AND
RESULTS: Epicardial activation patterns during attempted electrical defibrillation were studied in 18 Langendorff-perfused rabbit hearts at baseline, after 5-minute no-flow global ischemia and after 10-minute reperfusion. DFT(50) (voltage required to achieve 50% probability of successful defibrillation) was determined at each stage. Defibrillation was considered successful if postshock sinus/idioventricular rhythm was present. Prolonged global ischemia converted type 1 VF (multiple wandering wavelets) into type 2 VF (repetitive epicardial breakthroughs, REBs). The mean DFT(50) after 5-minute ischemia (96 +/- 39 V) was significantly lower when compared with that at baseline (154 +/- 47 V, P < 0.0001) and after 10-minute reperfusion (145 +/- 47 V, P < 0.001). However, the incidence of early (within 10 seconds) VF recurrence after successful shock during prolonged global ischemia (23 of 78, 29.5%) was much higher than that at baseline (2 of 60, 3.3%) and after 10-minute reperfusion (5 of 63, 7.9%; P < 0.0001). Mapping data showed that the VF wavefronts during prolonged global ischemia were initially halted by the shock, followed by one to five ventricular escape beats. These beats then triggered REBs and early VF recurrence. In eight out of 11 episodes, the REBs before and after successful shock arose from the same location near the interventricular septum.
CONCLUSIONS: There is a significant reduction of DFT(50) during prolonged global ischemia. However, defibrillation appears to fail when the preexisting REBs near the interventricular septum induce early VF recurrence. Shock per se cannot eliminate the substrates of these REBs.