Background: Transplant coronary artery disease is the major factor limiting long-term survival after cardiac transplantation. Both intravascular ultrasound imaging (IVUS) and intracoronary flow studies have been used to assess the morphologic and functional importance of the disease. However, the impact of epicardial intimal thickening, as quantitated by IVUS, on the resistance vessel response to adenosine has not been explored.
Methods and results: Seventy-six coronary arteries without angiographically overt coronary disease (diameter stenosis visually, < or =50%) were studied with both IVUS and intracoronary Doppler in 54 patients 0.5 to 127 months after transplantation. Mean intimal index and mean lumen cross-sectional area (CSA) were determined by IVUS, and the average was obtained for every coronary artery. Coronary flow average peak velocity (APV) was obtained by Doppler before and after administration of 16 microg adenosine to calculate coronary flow velocity reserve (CFVR) and coronary vascular resistance index (CVRI). The hyperemic pressure-flow velocity ratio (hyperemic mean aortic pressure/hyperemic APV) as an index of minimal coronary resistance was further derived. The intimal index (mean, 20.0+/-10%) did not correlate with either CFVR (mean, 2.9+/-0.7, r=.12) or CVRI (mean, 0.33+/-0.1, r=.16). However, a significant correlation between the intimal index and the hyperemic pressure-flow velocity ratio (mean, 1.52+/-0.47 mm Hg/cm/s, r=.74, P<.0001) was found. The hyperemic pressure-flow velocity ratio was not influenced by the presence or absence of left ventricular hypertrophy or a mild acute rejection period (International Society for Heart and Lung Transplantation grades IA and IB).
Conclusions: This study shows that in patients without angiographically overt coronary disease, the degree of epicardial intimal thickening as quantified by IVUS did not predict the adenosine vasodilator response, when determined by commonly used parameters such as CFVR and CVRI. The hyperemic pressure-flow velocity ratio best reflected the functional significance of transplant coronary artery disease.