A probability analysis of heart rate variability for heart transplant and myocardial infarction patients and for healthy subjects

We present a probability analysis of RR interval series. The analysis is based on a subdivision of the RR interval series into segments - here called m-segments - ranging from one local RR maximum value to the consecutively following local RR maximum value; such segments represent full cycles of acceleration followed by deceleration of the heart rate. We analyze the properties of m-segments in terms of the probability of observing j RR values in the segment and in terms of the probability of observing a change of Δj in going from one m-segment to the following m-segment. We also calculate the rms-values, σ_m, of the m-segments and introduce an entropy measure to characterize the RR interval series. Further, we present a simple model for phase-space-trajectory plots for RR interval series and an estimate of the spectral properties in terms of the parameters j and σ_m. The results are based on 24-hour RR interval series for ten heart transplant patients, with a total of 23 recordings, for 326 myocardial infarction patients and 104 healthy subjects. The results obtained show characteristic differences between the behavior of the three groups, but no attempt at a clinical interpretation is made.