Every sixth death in industrialised countries occurs because of cardiac
arrhythmias like ventricular tachycardia (VT) and ventricular fibrillation
(VF). There is growing consensus that VT is associated with an unbroken spiral
wave of electrical activation on cardiac tissue but VF with broken waves,
spiral turbulence, spatiotemporal chaos and rapid, irregular activation. Thus
spiral-wave activity in cardiac tissue has been studied extensively.
Nevertheless many aspects of such spiral dynamics remain elusive because of the
intrinsically high-dimensional nature of the cardiac-dynamical system. In
particular, the role of tissue heterogeneities in the stability of cardiac
spiral waves is still being investigated. Experiments with conduction blocks in
cardiac tissue yield a variety of results: some suggest that blocks can
eliminate VF partially or completely, leading to VT or quiescence, but others
show that VF is unaffected by obstacles. We propose theoretically that this
variety of results is a natural manifestation of a fractal boundary that must
separate the basins of the attractors associated, respectively, with VF and VT.
We substantiate this with extensive numerical studies of Panfilov and Luo-Rudy
I models, where we show that the suppression of VF depends sensitively on the
position, size, and nature of the inhomogeneity.Comment: 9 pages, 5 figures
