CORONARY VASOMOTILITY AND MYOCARDIAL BLOOD-FLOW EARLY AFTER HEART-TRANSPLANTATION

Serotonin constricts coronary arteries with endothelial dysfunction, a common abnormality in cardiac transplant recipients. To assess whethe r endothelial dysfunction is associated with myocardial blood flow (MB F) abnormalities, 24 patients were studied 1 to 12 months after transp lantation. Serotonin in increasing doses (1, 10, and 20 mu g/min for 2 .5 min each) was infused into the coronary circulation. Diameters were measured by quantitative angiography. Fourteen patients (group A) had a pronounced artery constriction (diameter reduction >40%), while in 10 other patients (group B), such a constriction was never reached. No patient had evidence of rejection and all had angiographically normal coronary arteries. MBF was measured at rest and after intravenous dip yridamole with dynamic nitrogen-13 ammonia positron emission tomograph y (PET). The resting MBF was higher in group A than in group B (94 +/- 12 vs 74 +/- 15 ml/min/100 g of tissue; p <0.05). During dipyridamole , MBF was not significantly different (191 +/- 53 vs 184 +/- 64 ml/min /100 g; p = NS). Coronary flow reserve (the ratio of perfusion after d ipyridamole to perfusion at rest) was significantly lower in group A t han in group B (2.08 +/- 0.54 vs 2.66 +/- 0.57; p <0.05). Thus, corona ry hypersensitivity to serotonin in cardiac transplant recipients is a ssociated with elevated resting MBF and reduced coronary flow reserve. Immune mechanisms inducing endothelial injuries and inflammation-rela ted hyperemia may account for these abnormalities.