Relationship between dobutamine-induced regional wall motion abnormalities and coronary flow reserve in heart transplant patients without angiographic coronary artery disease

Background: Regional wall motion abnormalities (RWMA) demonstrated by dobutamine stress echocardiography (DSE) are a sensitive predictor of coronary artery disease (CAD) in heart transplant recipients. However, RWMA have been shown to occur in patients with angiographically "normal" coronary arteries. The reasons for this are unknown. We sought to determine if abnormal responses to dobutamine in this setting can be explained by microvascular dysfunction in the coronary circulation as detected by decreased coronary flow reserve (CFR). Methods: Twenty-six consecutive heart transplant patients were evaluated prospectively. Five of 26 (19.2%) patients (seven coronary arteries) were excluded for poor acoustic windows on echocardiography. Another three patients were excluded for angiographically apparent CAD. CFR and wall motion score index (WMSI) derived from DSE were measured in the remaining 18 patients and formed the basis of this study. Patients were divided into two groups based on the absence (Group 1; n = 5) or. presence (Group 2; n = 13) of RWMA on DSE. CFR was measured with the Doppler Flo-Wire in 34 coronary arteries (18 paltients) and correlated with WMSI. Results: In Group 1 patients, CFR measured in eight coronary arteries was normal (2.6 +/- 0.4). In Group 2 patients, CFR measured in 26 coronary arteries also was normal (2.2 +/- 0.6; p = NS vs Group 1). In Group 2, CFR was measured in 20 of 24 vessels assigned to segments that developed RWMA. Only 6 of these 20 vessels (30%) had abnormal CFR. Overall, there was no correlation between decreased CFR and the presence of RWMA induced by dobutamine. Conclusions: These data suggest that, in cardiac transplant patients with angiographically "normal" coronary arteries, inducible wall motion abnormalities during DSE cannot be attributed to coronary microvascular dysfunction as manifested by, decreased CFR.