LOSS OF THE CORONARY MICROVASCULAR RESPONSE TO ACETYLCHOLINE IN CARDIAC TRANSPLANT PATIENTS

Background. The coronary arteries of transplanted hearts frequently develop accelerated diffuse arteriosclerosis. The effects of this disease on resistance vessel function are unknown. Methods and Results. To investigate the integrity of endothelium-dependent small-vessel vasodilation in transplanted hearts, coronary blood flow (CBF) responses to the endothelium-dependent dilator acetylcholine (10(-8) to 10(-6) M) and the essentially endothelium-independent dilator adenosine (10(-6) to 10(-4) M) were assessed in 40 studies of 29 transplant patients 1-3 years after transplantation and in seven nontransplanted controls. CBF was measured at constant arterial pressure with a Doppler catheter in the left anterior descending coronary artery. Controls, year 1 transplant patients, and year 2 transplant patients had similar increases in CBF in response to acetylcholine (232+/-40%, 200+/-41%, and 201+/-54%, respectively; p=NS), whereas year 3 transplant patients had increased CBF of only 100+/-39% (p<0.05 versus controls). An index of the proportion of CBF reserve attributable to endothelium-dependent dilation was obtained by normalizing each patient's peak acetylcholine flow response by the peak adenosine flow response. In patients receiving both acetylcholine and adenosine, endothelium-dependent flow responses declined over time [57+/-9% in controls, 56+/-10% for year 1, 47+/-12% for year 2, and 29+/-9% for year 3 (p<0.05 versus controls)]. An increased mean cyclosporine level (range, 99-261 ng/ml) (r=0.67, p=0.004) and increased transplant recipient age (range, 20-63 years) (r=0.51, p=0.004) predicted a preserved endothelium-dependent microvascular response. Conclusions. Thus, microvascular endothelium-dependent dilation deteriorates over time in the transplanted heart, which may reflect underlying graft arteriosclerosis and contribute to ischemic damage of the myocardium.