TRANSIENT MYOCARDIAL-ISCHEMIA IN PATIENTS WITH CHRONIC ANGINA - RELATION TO HEART-RATE CHANGES AND VARIABILITY IN EXERCISE THRESHOLD

This study was undertaken to assess the relation of ambulatory myocard ial ischemia to heart rate changes and variability in exercise thresho ld in patients with chronic angina. The study involved 118 patients wi th chronic angina and proven coronary artery disease who had a 'positi ve' exercise test result. All patients underwent a first exercise test followed by a 48-h period of ambulatory electrocardiographic monitori ng. A second exercise test was performed 4 days later. A total of 101 ischemic episodes were recorded in 35 patients. The heart rate at the appearance of 1-mm ST segment depression during ambulatory electrocard iographic monitoring was greater than or equal to 20 beats/min lower t han that during exercise testing in 58 ischemic episodes (57%, Group A ), 10-19 beats/min lower in 26 (26%, Group B), and less than or equal to 9 beats/min lower or higher in 17 (17%, Group C). Thirty-five perce nt of the Group A ischemic episodes, 69% of Group B, and 71% of Group C were preceded by an increase in heart rate of greater than or equal to 10 beats/min. Thirty patients showed a variable exercise threshold. The prevalence of Group A and B ischemic episodes was not significant ly different in patients with fixed or variable exercise threshold, wh ereas that of Group C episodes was 22% in the former and 0% in the lat ter (P = 0.036). These results suggest that increased coronary tone ma y be one of the mechanisms contributing to modulate the occurrence of transient myocardial ischemia in most patients with chronic angina and transient myocardial ischemia at ambulatory electrocardiographic moni toring. This occurs regardless of whether the patients have a variable or fixed exercise threshold.