Ventricular fibrillation: evolution of the multiple-wavelet hypothesis

Every heartbeat is preceded by an electrical wave of excitation that rapidl y propagates through the cardiac muscle, triggering mechanical contractions of cardiac myocytes. Abnormal propagation of this wave causes severe cardi ac arrhythmias. The most dangerous of these is ventricular fibrillation, th e leading cause of sudden death in the industrialized world. It is well est ablished that ventricular fibrillation is a result of turbulent; propagatio n of the electrical excitation wave. However, despite more than a century o f investigation, the precise mechanism of its initiation and maintenance re mains largely unknown. Novel, experimental tools for the visualization of t he excitation wave as well as advanced three-dimensional computer models of the heart, which have become available in recent years, have intensified a ttempts to solve the puzzle of ventricular fibrillation. These efforts have revealed significantly different manifestations of ventricular fibrillatio n, suggesting that multiple mechanisms are responsible for this arrhythmia. Several new hypotheses have been put forward recently that deviate conside rably from Moe's standard hypothesis of fibrillation, which has dominated t he field for almost four decades. One of the hypotheses that has been most actively discussed is the spiral-breakup (also called the restitution) hypo thesis. This hypothesis may lead to a breakthrough in our understanding of the factors that; cause this deadly arrhythmia and provide a constructive a pproach to the development of efficient antifibrillatory drugs.