Current concepts on ventricular fibrillation: A Vicious Circle of Cardiomyocyte Calcium Overload in the Initiation, Maintenance, and Termination of Ventricular Fibrillation

Based on recent experimental studies, this review article introduces the novel concept that cardiomyocyte Ca(2+) and ventricular fibrillation (VF) are mutually related, forming a self-maintaining vicious circle in the initiation, maintenance, and termination of VF. On the one hand, elevated myocyte Ca(2+) can cause delayed afterdepolarizations, triggered activity, and consequently life-threatening ventricular tachyarrhythmias in various pathological conditions such as digitalis toxicity, myocardial ischemia, or heart failure. On the other hand, VF itself directly and rapidly causes progressive myocyte Ca(2+) overload that maintains VF and renders termination of VF increasingly difficult. Accordingly, energy levels for successful electrical defibrillation (defibrillation thresholds) increase as both VF and Ca(2+) overload progress. Furthermore, VF-induced myocyte Ca(2+) overload can promote re-induction of VF after defibrillation and/or postfibrillatory myocardial dysfunction (postresuscitation stunning) due to reduced myofilament Ca(2+) responsiveness. The probability of these adverse events is best reduced by early detection and rapid termination of VF to prevent or limit Ca(2+) overload. Early additional therapy targeting transsarcolemmal Ca(2+) entry, particularly during the first 2 min of VF, may partially prevent myocyte Ca(2+) overload and thus, increase the likelihood of successful defibrillation as well as prevent postfibrillatory myocardial dysfunction.