Evidence for deterministic chaos in heart rhythms

It is postulated that deterministic chaos modulates beat-to-beat heart rate (HR). The prediction method of Sugihara and May (1990) was applied to 1000 R-R intervals from 14 healthy human subjects and 15 patients with acute myocardial infarction (AMI). The correlation integral of Grassberger and Procaccia (1983) was constructed for each subject. No evidence was found for an attractor having a dimension <4. Short term predictability was evident in the HR data. Mean slope of predictability (MSP) was lower in patients compared to normals. The MSP may be a useful parameter for classifying neurocardiac control in healthy subjects and patients with AMI. There was no correlation between MSP and the standard deviation (SD) of the mean HR. MSP and SD may provide a more reliable characterization of the neurocardiac control than the SD alone.<>