Effects of moderate coronary stenosis on myocardial flow reserve in man and in the dog.

The influence of coronary stenosis on resting blood flow (201Tl-uptake) and myocardial flow reserve (bicycle ergometry) is studied in 18 patients with coronary disease. Severe coronary stenosis of 75--90% caused a reduced 201Tl-uptake both at rest and peak exercise. In contrast to this group patients with a 50--60% stenosis have a normal scintigram at rest but focal defects of 201Tl-uptake at peak exercise. Results are compared with experimental data obtained after acute coronary constriction and simultaneous coronary dilatation (myocardial flow reserve, MFR) in 12 dogs. 60% coronary constriction causes a 37% decrease of poststenotic MFR measured with tracer microspheres. Changes of transmural flow distribution (endo/epi ratio) are minor in the left ventricular free wall but significant in the poststenotic septum (endo/epi = .84). It is concluded that even a moderate coronary stenosis of 60% not affecting resting blood flow becomes "critical" under conditions of high flow velocities.