Myocardial ischemia evokes autonomic reflexes, which in turn can influence the ischemic events. The heart rate variability (HRV) provides a useful, noninvasive clinical tool for studying the autonomic activity. Only a few studies have reported results on the spectral modifications during myocardial ischemia in humans. Our aim was to evaluate the changes in the RR interval variability during dipyridamole infusion and dipyridamole-induced myocardial ischemia.

The study population included 38 patients, with stable or unstable angina (group AP, n=20), and sex matched healthy controls (group C, n=18). The ECG was continuously recorded before and during the dipyridamole infusion, for use in a later off-line spectral analysis. We investigated the following variables: the mean and variance of the RR interval, low and high frequency powers (LF and HF, respectively) and their normalized units (LFnu and HFnu), the LF ratio (the ratio of the LF power at peak stress and in the basal state), the HF ratio and the LF/HF ratio. The changes in the HRV parameters were analyzed and compared, before and after the dipyridamole infusion, for both groups.

The dipyridamole injection was characterized by a reduction in all the spectral components in group C. In group AP, the dipyridamole injection significantly decreased the HF power and HFnu, but increased the LF power, with a resultant significant increase in the LFnu and LF/HF ratio. The LF ratio decreased from 1.00±0.00 to 0.55±0.17 (p<0.017) during the dipyridamole infusion in group C, but increased from 1.00±0.00 to 2.84±0.8 (p<0.032) in group AP. The difference in the LF ratio between groups AP and C was significant (p<0.001).

Information on myocardial ischemia can be extracted from the analysis of the HRV. The LF ratio was the most valuable parameter for discriminating the patients from the control subjects.