Changes of Heart Rate Variability during Dipyridamole Infusion and Dipyridamole-Induced Myocardial Ischemia: Clinical Usefulness for the Detection of Myocardial Ischemia

BACKGROUND AND OBJECTIVE: 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. SUBJECTS AND METHODS: 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. RESULTS: 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). CONCLUSION: 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.

Difference of QT Dispersion between Patients with Ischemic and Idiopathic Dilated Cardiomyopathy

BACKGROUND AND OBJECTIVES: QT dispersion (QTd) is defined as the difference between the maximum and minimum QT interval in any of the 12 leads of the surface ECG. QTd has been shown to reflect regional variations in ventricular repolarization. Ischemic dilated cardiomyopathy (DCM) may lead to more spatial and temporal dispersion in ventricular repolarization than idiopathic DCM. The purpose of this study was to determine the difference of QTd between patients who had ischemic and idiopathic DCM. MATERIALS AND METHODS: The study population included 30 patients with ischemic DCM and 30 with idiopathic DCM. All standard 12-lead ECGs were examined prospectively by two observers who were unware of the patient's details. RESULTS: QTd in ischemic DCM was significantly higher than that in idiopathic DCM (63+/-32 vs. 44+/-26 msec, p=0.012) and JTd in ischemic DCM was significantly higher than that in idiopathic DCM (48+/-21 vs. 36+/-22 msec, p=0.036). Results did not change when Bazett's QTc and JTc was substituted for QT (QTcd:69+/-33 vs. 52+/-28 p=0.039) and JT (JTcd:56+/-21 vs. 41+/-25 p=0.043). CONCLUSION: Ischemic DCM has increased spatial inhomogeneity of repolarization probably due to more regional myocardial damages compared with idiopathic DCM. The value of QT dispersion as an easily accessible, non-invasive method in predicting the risk of life threatening arrhythmia and overall mortality in patients with dilated cardiomyopathy must be confirmed in prospective trials.