DETERMINATION OF REGIONAL MYOCARDIAL BLOOD-FLOW WITH N-13 AMMONIA POSITRON EMISSION TOMOGRAPHY DURING LOW-GRADE EXERCISE FOR EVALUATING CORONARY-ARTERY STENOSIS

We measured regional myocardial blood flow (RMBF) by positron emission tomography (PET) with N-13-ammonia at rest and during low-grade exerc ise using a bicycle ergometer fixed at 25 watts for 6.5 min. The ische mic area with severe coronary artery stenosis was evaluated in terms o f quantitative RMBF. The study was performed in 46 subjects consisting of 19 patients with old myocardial infarction, 20 with effort angina pectoris, and 7 normal individuals. RMBF was calculated using the radi oactivity in myocardial tissue measured by PET and the radioactivity i n arterial blood. The PET data were compared with coronary arteriograp hic findings and ECG findings. When the analysis was restricted to the anterior wall of the myocardium, it was found that exercise caused RM BF to increase by 44.9% (n=28) in normal area, to increase by 23.3% (n =37) in severely stenotic area (stenosis greater-than-or-equal-to 90%) , and to decrease by 17.4% (n=20) in infarcted area. When we considere d only the infarcted area of the entire heart, exercise caused RMBF to decrease by 26.6% (n=30) in the area of angiographically positive col laterals, and to increase by 0.8% (n=31) in the area of negative colla terals. Thus, we were able to quantitate the degree of ischemia in myo cardium that was associated with severe coronary artery stenosis. By a pplication of low-grade exercise, RMBF in normal myocardium increased, while RMBF in myocardium perfused by collaterals decreased.