Mechanisms underlying ventricular tachycardia and its transition to ventricular fibrillation in the structurally normal heart

Reentrant ventricular tachycardia (VT) is the most common sustained arrhyth mia leading to ventricular fibrillation (VF). However, despite more than a century of research, the mechanism(s) of the conversion from reentrant VT t o VF have not been elucidated. Based on their different electrocardiographi c appearance, reentrant VT and VF have traditionally been thought of as res ulting from two widely different mechanisms. Whereas VT is seen as a rapid but well organized process whereby the excitation wave rotates about a sing le well-defined circuit, fibrillation has been described as turbulent cardi ac electrical activity, resulting from the random and aperiodic propagation of multiple independent wavelets throughout the cardiac muscle. Recently, the application of concepts derived from the theory of non-linear dynamics to the problem of wave propagation in the heart and the advent of modern hi gh-resolution mapping techniques. have led some investigators to view VT an d VF in terms of a single mechanism, whereby the self-organization of elect rical waves forms 'rotors' that give rise to rapidly rotating spiral waves and results in either VT or VF, depending on the frequency of rotation and on the interaction of wave fronts with the cardiac muscle. As such, monomor phic VT is thought to result from a stationary rotor, whose frequency of ro tation is within a range that allows 1:1 excitation of both ventricles. On the other hand, VF is thought to result from either a single rapidly drifti ng rotor, or a stationary rotor whose frequency of excitation is exceedingl y high, thus resulting in multiple areas of intermittent block and giving r ise to complex patterns of propagation with both deterministic and stochast ic components. This article reviews the prevailing theories for the mainten ance of VF, and discusses recently proposed mechanisms underlying transitio ns between VT and VF. (C) 2001 Elsevier Science B.V. All rights reserved.