Determination of regional myocardial blood flow with 13N-ammonia positron emission tomography during low-grade exercise for evaluating coronary artery stenosis.

Abstract

We measured regional myocardial blood flow (RMBF) by positron emission tomography (PET) with 13N-ammonia at rest and during low-grade exercise using a bicycle ergometer fixed at 25 watts for 6.5 min. The ischemic area with severe coronary artery stenosis was evaluated in terms of 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 radioactivity in myocardial tissue measured by PET and the radioactivity in arterial blood. The PET data were compared with coronary arteriographic findings and ECG findings. When the analysis was restricted to the anterior wall of the myocardium, it was found that exercise caused RMBF to increase by 44.9% (n = 28) in normal area, to increase by 23.3% (n = 37) in severely stenotic area (stenosis > or = 90%), and to decrease by 17.4% (n = 20) in infarcted area. When we considered only the infarcted area of the entire heart, exercise caused RMBF to decrease by 26.6% (n = 30) in the area of angiographically positive collaterals, and to increase by 0.8% (n = 31) in the area of negative collaterals. Thus, we were able to quantitate the degree of ischemia in myocardium that was associated with severe coronary artery stenosis. By application of low-grade exercise, RMBF in normal myocardium increased, while RMBF in myocardium perfused by collaterals decreased.