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

BackgroundMeasurement 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. ObjectivesWe investigated the relationship between coronary arteries of different diameters and hMVRI. MethodThirty 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 (DQCA) was analyzed by quantitative coronary angiography (QCA). Coronary blood flow (CBFQCA) was calculated as {pi}DQCA2/4 (0.5xAPV) and hMVRI as distal coronary pressure (Pd) divided by CBFDQCA during maximal hyperemia. ResultsThe 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 CBFQCA and hMVRIQCA. Although the correlation between CBFQCA and APV was weak in all arteries, CBFQCA divided into three groups according to DQCA showed very strong correlations with APV. Slopes of the straight line between APV and CBFQCA 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 CBFQCA was high for LAD and RCA, but weak for the left circumflex artery. ConclusionsEvaluation of MR in coronary branches requires consideration of vessel diameter.