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

Abstract

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...