Spectral behaviour of heart rate variability in acute ischemic episodes

Wavelet transforms have been used to study the transitory behaviour of RR time series in correspondence to acute ischemic episodes. The number of samples and the sampling frequency were chosen in order to cover the heart rate variability in four frequency bands: VULF, LF, HF1, HF2. The Holter recordings often subjects with no previous myocardial infarction were analysed automatically and 24 hr RR and ST time series were produced. Signalled ST displacements were visually checked and eventually recognized as ischemic episodes. In all cases a well defined pattern of activities increasing, flattening and then increasing again, centered around the deep of the ST level is observed. This method can be used to study the behaviour of the autonomic nervous system and the sympatho-vagal balance in correspondence to ischemic episodes, exploring heart rate variability over short time intervals.