Intracellular Calcium and Vulnerability to Fibrillation and Defibrillation in Langendorff-Perfused Rabbit Ventricles

Background— The role of intracellular calcium (Cai) in defibrillation and vulnerability is unclear. Methods and Results— We simultaneously mapped epicardial membrane potential and Cai during shock on T-wave episodes (n=104) and attempted defibrillation episodes (n=173) in 17 Langendorff-perfused rabbit ventricles. Unsuccessful and type B successful defibrillation shocks were followed by heterogeneous distribution of Cai, including regions of low Cai surrounded by elevated Cai (“Cai sinkholes”) 31±12 ms after shock. The first postshock activation then originated from the Cai sinkhole 53±14 ms after the shock. No sinkholes were present in type A successful defibrillation. A Cai sinkhole also was present 39±32 ms after a shock on T that induced ventricular fibrillation, followed 22±15 ms later by propagated wave fronts that arose from the same site. This wave propagated to form a spiral wave and initiated ventricular fibrillation. Thapsigargin and ryanodine significantly decreased the upper limit of vulnerab...