The Relationship of Capillary Blood Flow Assessments with Real Time Myocardial Perfusion Echocardiography to Invasively Derived Microvascular and Epicardial Assessments

Abstract

The basis for abnormal microvascular flow responses to demand stress in coronary artery disease (CAD) is affected by resistance changes at both the epicardial stenosis level and within the downstream capillary network. We hypothesized that abnormal microvascular perfusion (MVP) responses during demand stress in patients with intermediate coronary stenoses occur when fractional flow reserve (FFR) across the epicardial stenosis is normal, because of increased microvascular resistance. In 49 coronary arteries of 41 patients with intermediate stenoses (40%-80%) who were referred for both coronary angiography and demand stress MVP assessment, invasive coronary hemodynamics were obtained across the stenosis to measure FFR, coronary flow reserve (CFR), and hyperemic microvascular resistance (HMR) during adenosine infusion. MVP in each coronary artery territory (CAT) during demand stress was evaluated by an independent expert reviewer blinded to clinical and angiographic data. Thirty-four of the 49 CATs with intermediate stenoses exhibited abnormal MVP. Although the sensitivity of MVP was high for detecting abnormal FFR (100%), FFR<0.8 was observed in only 15 of the 34 vessels that exhibited abnormal MVP (positive predictive value 44%). However, HMR was abnormal in 32 of 34 vessels (94%) with abnormal MVP (positive predictive value, 94%). Although abnormal MVP has high sensitivity for detecting abnormal FFR, MVP is frequently abnormal when FFR is normal. In a large percentage of these patients, invasive assessments of microvascular resistance are abnormal.