Effect of cardiac resynchronization therapy on hyperemic microvascular resistance in the left anterior descending coronary artery (LAD) and left circumflex coronary artery (LCx). Hyperemic microvascular resistance index (HMR) was significantly lower during biventricular pacing (BiV) than during Control (LAD, 1.76 ± 0.47 vs. 1.54 ± 0.45; P < 0.001; LCx, 1.92 ± 0.42 vs. 1.73 ± 0.31; P = 0.003).