Complex dynamics of cardiac arrhythmias

In the case of a benign but very active cardiac arrhythmia often observed in healthy subjects, the behavior of the ventricular extrasystoles during long-term electrocardiographic recording was carefully scrutinized using the facilities of complex computerized programs of analysis. The presence or the absence of the extrasystoles, their distribution with respect to the normal beats, their time relationships, and the existence or the absence of a repetitive activity after the initial extrasystole follow complex, interactive rules that essentially depend on two determinants: the cardiac frequency as such (rate-dependence) and the autonomic nervous system (adrenergic dependence). It can be concluded, at variance from the random distribution suggested by a superficial examination, that an in-depth study allows the complex rules conditioning the various types and patterns of extrasystoles to be unearthed. Precise quantitative regularities underly the dynamics, and observing such rules gives the cardiologist hopes that one might distinguish various physiological mechanisms from a careful consideration of the dynamics. Collaboration of cardiologists and nonlinear dynamicists is needed to understand the origin of complex cardiac rhythms and to sort out the roles of chance and determinism in their genesis.