Decrease of cardiac chaos in congestive heart failure

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Abstract
The electrical properties of the mammalian heart undergo many complex transitions in normal and diseased states1,2,3,4,5,6,7. It has been proposed that the normal heartbeat may display complex nonlinear dynamics, including deterministic chaos8,9, and that such cardiac chaos may be a useful physiological marker for the diagnosis10,11,12 and management13,14 of certain heart trouble. However, it is not clear whether the heartbeat series of healthy and diseased hearts are chaotic or stochastic15,16,17, or whether cardiac chaos represents normal or abnormal behaviour18. Here we have used a highly sensitive technique, which is robust to random noise, to detect chaos19. We analysed the electrocardiograms from a group of healthy subjects and those with severe congestive heart failure (CHF), a clinical condition associated with a high risk of sudden death. The short-term variations of beat-to-beat interval exhibited strongly and consistently chaotic behaviour in all healthy subjects, but were frequently interrupted by periods of seemingly non-chaotic fluctuations in patients with CHF. Chaotic dynamics in the CHF data, even when discernible, exhibited a high degree of random variability over time, suggesting a weaker form of chaos. These findings suggest that cardiac chaos is prevalent in healthy heart, and a decrease in such chaos may be indicative of CHF.