FUNCTIONAL-ROLE OF CORONARY COLLATERALS WITH EXERCISE IN INFARCT-RELATED MYOCARDIUM

We evaluated the regional myocardial blood flow in collateral dependen t infarct-related areas to examine the functional role of coronary col laterals, Regional myocardial blood flow was measured by positron emis sion tomography with N-13-ammonia at rest and during low-grade exercis e (bicycle ergometer fixed at 25 W for 6.5 min). The study was perform ed in 24 subjects, consisting of 19 patients with prior myocardial inf arction, and five normal individuals. Regional myocardial blood flow w as calculated using the radioactivity in myocardial tissue measured by positron emission tomography and the radioactivity in arterial blood. Concerning the infarct related area, the exercise caused myocardial b lood flow to decrease by 18.4% (P < 0.01) in the collateral-dependent areas (n = 8) of angiographically positive collaterals, and to increas e by 14.4% (P = not significant) in the areas (n = 10) of negative col laterals. Four patients in whom the myocardial blood flow in all walls , including the normal areas, decreased with exercise were excluded fr om this evaluation. Myocardial blood flow in collateral-dependent infa rct-related areas appeared to decrease transiently by low-grade exerci se. Our results suggest that collaterals increase the incidence of exe rcise-induced ischemia, but may protect the infarct related but viable myocardium from necrosis.