MYOCARDIAL BLOOD-FLOW AT REST AND DURING PHARMACOLOGICAL VASODILATIONIN CARDIAC TRANSPLANTS DURING AND AFTER SUCCESSFUL TREATMENT OF REJECTION

Background The relative intracoronary flow reserve has been found to b e reduced during acute transplant rejection, but the effects of reject ion on absolute flows at rest and during hyperemia have not been estab lished previously. This has now become possible through noninvasive qu antification of myocardial blood flow with positron emission tomograph y. Methods and Results Myocardial blood flow (MBF) at rest and during dipyridamole-induced hyperemia was quantified in 10 transplant patient s (group A) during an acute, biopsy-proven rejection episode and again after successful immunosuppressive treatment and in 6 transplant pati ents (group B) without prior rejection episodes. In group A patients, MBF during rejection averaged 1.7+/-0.3 mL.min(-1).g(-1) at rest and 2 .5+/-0.9 mL.min(-1).g(-1) during hyperemia; after recovery, MBF at res t had declined to 1.2+/-0.3 mL.(-1).g(-1) (P<.001) but had increased t o 3.9+/-1.1 mL.(-1).g(-1) (P<.001) during hyperemia. Flows after recov ery from rejection were similar to those in the group B patients (0.9/-0.2 and 3.9+/-0.7 mL.min(-1).g(-1)). Flow reserve in the group A pat ients was only 1.5+/-0.5 during rejection but improved to 3.4+/-0.9 at recovery (P<.001) and thus remained lower than in the control patient s (4.5+/-0.7, P<.05). Minimal coronary resistance during dipyridamole vasodilation was elevated during rejection (40+/-11 mm Hg.mL(-1).min(- 1).g(-1)); after recovery, it no longer differed from that in the grou p B patients (26+/-11 versus 22+/-4 mm Hg.mL(-1).min(-1).g(-1)). MBF d uring rejection was increased relative to cardiac work, as demonstrate d by significantly higher ratios of blood flow to rate-pressure produc t than those at recovery and in the control patients. Conclusions A de crease in hyperemic and an increase in resting myocardial blood flow, in excess to cardiac work, account for the previously reported reducti on in coronary flow reserve. Because both alterations improve with ant irejection treatment, they may reflect reversible alterations, presuma bly of endothelial function, local coagulation, and edema. The comprom ise in flow reserve and hyperemic flows may contribute to acute and ch ronic injury from rejection and thus provides a rationale for exercise restriction during rejection. The results further suggest a potential role for serial noninvasive flow measurements to guide immunosuppress ive therapy.