AUTONOMIC EFFECTS OF DIPYRIDAMOLE STRESS-TESTING ON FREQUENCY-DISTRIBUTION OF RR AND QT INTERVAL VARIABILITY

Transient myocardial ischemia and associated changes in the autonomic nervous system may influence heart rate and ventricular repolarization to variable degrees. This study evaluated the effect of dipyridamole (DIP) induced ischemia on the autonomic balance by spectral analysis o f RR and QT intervals variability. Patients with coronary artery disea se undergoing DIP stress echocardiography were studied. From high reso lution ECG recordings, RR and QT interval measurements were performed by a dynamic template-matching algorithm. A time-variant analysis was used to estimate power in the LF (0.05-0.15 Hz) and in the HF (0.25-0. 4 Nz) band of RR and QT interval spectra. Patients were grouped in isc hemic and nonischemic subgroups based on the echocardiographic detecti on of wall-notion abnormalities. In patients without ischemia (n = 28) , DIP caused a decrease in LF power and an increase in HF power of the RR and QT interval variability indicating concordant changes of both intervals. In contrast, patients with inducible ischemia (n = 11) show ed a decrease in HF power of the RR interval spectra and an increase o f HF power of QT interval spectra. Furthermore, LF power was increased for RR but decreased for QT interval spectra. Our study suggests that DIP induced ischemia causes a loss of autonomic coupling between hear t rate and ventricular repolarization for sympathetic and parasympathe tic activities. This lability in ventricular repolarization may consti tute an arrhythmogenic substrate during acute ischemia in patients wit h coronary artery disease.