Nonlinear dynamic analysis of temporally heterogeneous action potential characteristics.

Rate-dependent bifurcations and aperiodic changes in action potential duration and amplitude were observed in periodically stimulated cardiac Purkinje and ventricular muscle cells isolated from dogs with quinidine-induced ventricular fibrillation and ventricular tachycardia. The slope of the action potential duration restitution curve was higher in the quinidine intoxicated fibers than in normal untreated fibers. Aperiodicity and bifurcations in action potential duration (APD) could not be observed in normal untreated cardiac fibers. The data suggest that induction of reentrant ventricular fibrillation and ventricular tachycardia could be brought about not by fixed but rather by changing alterations in cellular electrical activity. Theory based on nonlinear dynamics seems to provide a quantitative basis for such an analysis. This could have important implications in the issue of sudden cardiac death, a major problem in cardiology.