ASSESSMENT OF HEART-RATE-VARIABILITY CHANGES DURING DIPYRIDAMOLE INFUSION AND DIPYRIDAMOLE-INDUCED MYOCARDIAL-ISCHEMIA - A TIME-VARIANT SPECTRAL APPROACH

Objectives. We sought to evaluate changes in RR interval variability d uring dipyridamole infusion and dipyridamole-induced myocardial ischem ia. Background. Myocardial ischemia and the autonomic nervous system c an be mutually interdependent. Spectral analysis of RR interval variab ility is a useful tool in assessing autonomic tone. Methods. We used a time variant autoregressive spectral estimation algorithm that could extract spectral variables even in the presence of nonstationary signa ls. Two groups were considered: group A (patients with ischemia, n = 1 5) with effort or mixed angina, angiographically assessed coronary art ery disease and positive exercise and dipyridamole echocardiographic t est results, and group B (control subjects, n = 10) with normal exerci se and dipyridamole echocardiographic test results. We investigated th e following variables: RR interval mean and variance, low frequency (L F) and high frequency (HF) power in normalized units, LF ratio (LF/LF( basal) power), HF ratio (HF/HFbasal power) and LF/HF ratio. For each t est epoch, we calculated for group A and group B the mean value +/- SE of all indexes considered, Differences due to an effect either of gro up (ischemic vs. control) or of time (including both drug and ischemia effects) were analyzed by using analysis of variance for repeated mea surements. Results. Dipyridamole injection was characterized by a redu ction of all spectral components in negative test. The LF ratio was th e only variable able to discriminate patients with ischemia from contr ol subjects (p < 0.05), whereas a time effect was evident for both mea n 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 A from 1 +/- 0.00 to 15.41 +/- 6. 59, respectively, Results of an unpaired t test comparing the peak val ues of the ho groups were also statistically significant (p < 0.01). C onclusions. Our data show that time variant analysis of heart rate var iability evidences an increase in the low frequency ratio that allows differentiation of positive from negative test results, suggesting tha t the electrocardiogram may contain ischemia information unrelated to ST-T variations, even if their enhancement requires a more complex dat a processing procedure.