Residual coronary reserve despite decreased resting blood flow in patients with critical coronary lesions: A study by technetium-99m human albumin microsphere myocardial scintigraphy

Background. Experimental data demonstrate the persistence of a transmural vasodilator reserve in the face of depressed resting myocardial perfusion. The present study was designed to determine whether resting myocardial hypoperfusion indicates exhausted coronary reserve (CR). Methods and Results. Fifteen patients with stable angina, isolated left anterior descending coronary artery (LAD) stenosis, and no previous myocardial infarction were evaluated by means of ^99mTc human albumin microsphere scintigraphy. Regional myocardial perfusion and CR were assessed at baseline and after LAD papaverine (10-12 mg) by means of two microsphere injections in the left ventricle and compared with five normal subjects. Two 300-second scans were obtained with a mobile gamma camera positioned in the 70° left anterior oblique projection; actual microsphere distribution after papaverine was obtained by image subtraction. The two arterial input functions (basal and papaverine) were measured from the first-pass time-activity curves and validated with the reference arterial sample technique. From the comparison of circumferential profile analysis between patients and normal subjects, nine patients (group 1A) showed perfusion defects at rest (reduction of percent radioactivity below 2 SD of normal subjects) in the LAD territory, and the other six (group 1B) showed homogeneous perfusion. CR (papaverine/resting perfusion) was 3.8±0.2 and 1.51±0.27 in normal subjects and in ischemic patients, respectively (p<0.01). Despite resting hypoperfusion, group 1A showed a papaverine-recruitable CR similar to that of group 1B (1.57±0.33 and 1.43±0.16, respectively, p=NS). Conclusions. In patients with stable angina pectoris, isolated LAD stenosis, and no previous myocardial infarction, microsphere scintigraphy disclosed a high incidence of resting perfusion defects; in those patients, a residual CR was observed despite decreased resting blood flow.