Coronary microvascular resistance comparison of coronary branches with and without additional vascular diameter

Background Measurement of coronary microvascular resistance (MR) is essential for diagnosing nonocclusive coronary artery ischemia, but whether coronary branches of different diameters can be similarly assessed using hyperemic microvascular resistance index (hMVRI) calculated from average peak velocity (APV) remains unclear. Objectives We investigated the relationship between coronary arteries of different diameters and hMVRI. Method Thirty patients with suspected angina pectoris and nonobstructive coronary stenosis with fractional flow reserve >0.8 underwent evaluation of all coronary arteries using a Doppler velocity and pressure-equipped guidewire. Vessel diameter (D QCA ) was analyzed by quantitative coronary angiography (QCA). Coronary blood flow (CBF QCA ) was calculated as πD QCA 2 /4 (0.5×APV) and hMVRI as distal coronary pressure (Pd) divided by CBFD QCA during maximal hyperemia. Results The hMVRI was significantly higher for the right coronary artery (RCA) than for the left anterior descending artery (LAD), but no significant differences between arteries were seen for CBF QCA and hMVRI QCA . Although the correlation between CBF QCA and APV was weak in all arteries, CBF QCA divided into three groups according to D QCA showed very strong correlations with APV. Slopes of the straight line between APV and CBF QCA for small-, middle-, and large-diameter groups were 0.48, 0.30, and 0,21, respectively, with slope decreasing as diameter increased. The correlation between APV and CBF QCA was high for LAD and RCA, but weak for the left circumflex artery. Conclusions Evaluation of MR in coronary branches requires consideration of vessel diameter.