Assessment of Heart Rate Variability Changes During Dipyridamole Infusion and Dipyridamole-Induced Myocardial Ischemia: Time Variant Spectral Approach

Objectives. We sought to evaluate changes in RR interval variability during dipyridamole infusion and dipyridamole-induced myocardial ischemia. Background. Myocardial ischemi and the autonomic nervous system can be mutually interdependent. Spectral analysis of RR interval variability is useful tool in assessing autonomic tone. Methods. We used time variant autoregressive spectral estimation algorithm that could extract spectral variables even in the presence of nonstationary signals. Two groups were considered: group (patients with ischemia, n = 15) with effort or mixed angina, angiographically assessed coronary artery disease and positive exercise and dipyridamole echocardiographic test results, and group B (control subjects, n = 10) with normal exercise and dipyridamole echocardiographic test results. We investigated the following variables: RR interval mean and variance, low frequency (LF) and high frequency (HF) power in normalized units, LF ratio (LF/LFbasal power), HF ratio (HF/HFbasal power) and LF/HF ratio. For each test epoch, we calculated for group and group B the mean value ± SE of all indexes considered. Differences due to an effect either of group (ischemic vs. control) or of time (including both drug and ischemi effects) were analyzed by using analysis of variance for repeated measurements. Results. Dipyridamole injection was characterized by reduction of all spectral components in negative test. The LF ratio was the only variable able to discriminate patients with ischemi from control subjects (p < 0.05), whereas time effect was evident for both mean RR interval and high frequency power in normalized units (p < 0.05). The LF ratio decreased in group B from 1 ± 0.00 (basal) to 0.31 ± 0.22 (peak), and increased in group from 1 ± 0.00 to 15.41 ± 6.59, respectively. Results of an unpaired t test comparing the peak values of the two groups were also statistically significant (p < 0.01). Conclusions. Our dat show that time variant analysis of heart rate variability evidences an increase in the low frequency ratio that allows differentiation of positive from negative test results, suggesting that the electrocardiogram may contain ischemi information unrelated to ST-T variations, even if their enhancement requires more complex dat processing procedure.