HEART-RATE-VARIABILITY DEPRESSION IN PATIENTS WITH UNSTABLE ANGINA

The degree of reduction in heart rate variability (HRV) after myocardi al infarction has been shown to have prognostic significance, but HRV has not been studied extensively in patients with unstable angina. We assessed spectral and nonspectral measurements of HRV in 52 patients w ith unstable angina, 52 patients with acute myocardial infarction, and 41 normal subjects. The spectral bands of 0.04 to 0.15 Hz (low freque ncy), 0.15 to 0.4 (high frequency), and nonspectral parameters SDNN, S DANN, SDNN index, rMSSD, and pNN50 were calculated from continuous 24- hour ECGs. All measures of HRV were reduced in patients with acute cor onary syndromes compared to normal controls (p < 0.001), and there was no significant difference in measure of HRV between unstable angina a nd myocardial infarction patients. In patients with unstable angina wh o stabilized after admission, HRV had increased by the second 24 hours of monitoring. In contrast, HRV was further depressed in patients who had episodes of chest pain or transient ST-segment depression during the second 24 hours. rMSSD, pNN50, and SDNN index were lower in patien ts with unstable angina who had transient silent ischemia compared to those without silent ischemia. Of the patients with unstable angina, 4 died and 1 had nonfatal acute myocardial infarction within 11 months. HRV was lower in these patients than in patients without further card iac events.