DIPYRIDAMOLE CORONARY RESERVE AFTER ORTHO TOPIC HEART-TRANSPLANTATION- MEASUREMENT BY N-13 AMMONIA AND POSITRON EMISSION TOMOGRAPHY

Coronary transplant vasculopathy is known to be associated with an ear ly impairment of endothelium-dependent vasodilatation. In this study t he largely endothelium-independent dilator response to dipyridamole wa s evaluated in 22 patients 36 +/- 17 months after transplantation in r elation to their angiographic findings. The dipyridamole coronary rese rve was measured by N-13 ammonia and positron emission tomography (PET ). Transplant vasculopathy was suspected or evident in 13 of 22 patien ts by coronary angiography. Coronary reserve was lower in transplant r ecipients than in normal controls (2.3 +/- 0.9 vs. 4.7 +/- 1.4). Those with a normal angiogram had a near normal minimal coronary resistance (0.3 +/- 0.04 mm Hg . min . 100 g/ml) and a normalized coronary reser ve after correction for the increased resting blood flow (4.8 +/- 0.7) . However, in patients with angiographic vasculopathy, coronary reserv e was markedly reduced(1.8 +/- 0.7, corrected 2.7 +/- 1.0) and minimal coronary resistance was elevated (0.6 +/- 0.3, p < 0.001). Moreover, regional coronary reserve was homogeneously reduced throughout the myo cardium without a clear segmental relationship to angiographic stenose s. After testing of other factors known to influence coronary resistan ce, our data are compatible with diffuse obstructions of the microvasc ular bed that are associated with an angiographic visible vasculopathy . The evaluation of coronary reserve by dipyridamole and PET provides a useful extension of angiography in these patients.