Neurocardiology. Brain mechanisms underlying fatal cardiac arrhythmias.

Chaos theory may have a widespread application in medicine, from the analysis of protein structure at one end of the spectrum to fetal monitoring and the measurement of aging on the other. This application is especially on firm ground in cardiology, where it is simple and precise for the experimenter, and a primer exists for the clinician. As just presented, the point-correlation-dimension analysis of heartbeat variability is able to characterize the patterns of low-dimensional chaos produced by the heartbeat generator, a mechanism that is a composite of the voltage-dependent, neurotransmitter-dependent, and circulation-dependent ionic conductances that are all located in the myocardium where the heartbeat is formed. Most importantly, this deterministic measure of heartbeat variability is able to predict imminent lethal arrhythmogenesis with an accuracy that the more familiar stochastic measures do not have. This may arise because the PD2 is sensitive to the net degrees of freedom of the heartbeat generator, which, under the influence of the nerves and the coronary circulation, can be shifted so the resulting dynamics cause the initiation of lethal arrhythmogenesis. Application of chaos theory in neurology may be equally fruitful because the deterministic measures can discriminate among neuronal firing patterns, reveal subtle changes in brain waves, and be related to higher cognitive processes. Psychiatry also seems quite likely to benefit more and more from the application because the algorithms can discriminate schizophrenic brain functions from normal ones. Thus it can be expected that future applications will enable observation of biologic processes all along the brain-heart axis by which lethal ventricular fibrillation is regulated and perhaps even caused by its determination of the heartbeat dynamics. The subfield of neurocardiology has come a long way since it was first positively identified as an important research area. It took a lot of experiments to show how lethal cardiac arrhythmogenesis is involved with cerebral activities delivered over autonomic pathways. Although we do not yet fully understand the causal mechanism of lethal arrhythmogenesis, we may be getting close. It will become increasingly imperative for the clinical neurologist, along with the cardiologist, to understand the importance of neurocardiology in medical therapy and for the neurologist, along with the cardiologist and psychiatrist, to understand its importance in preventive treatments.