Persistent but reversible coronary microvascular dysfunction after bypass grafting

The effect of coronary artery bypass grafting (CABG) on absolute myocardial blood flow (MBF) has not been investigated previously. MBF (ml·min ^-1·g ^-1) was measured at rest and during hyperemia (0.56 mg/kg iv dipyridamole) using H ₂ ¹⁵O and positron emission tomography in eight patients with three-vessel disease before surgery and 1 and 6 mo after full revascularization. Baseline MBF was 0.87 ± 0.12 preoperatively and 1.04 ± 0.14 and 0.95 ± 0.13 at 1 and 6 mo after CABG, respectively (P <0.05, 6 mo vs. preoperatively). Hyperemic MBF was 1.36 ± 0.28 preoperatively and increased to 1.98 ± 0.50 and 2.45 ± 0.64 at 1 and 6 mo after CABG, respectively (P <0.01, 6 mo vs. preoperatively). Coronary vasodilator reserve (hyperemic/baseline MBF) increased from 1.59 ± 0.40 preoperatively to 1.93 ± 0.13 and 2.57 ± 0.49 at 1 and 6 mo, respectively (P <0.05, 6 mo vs. preoperatively). Minimal (dipyridamole) coronary resistance (mmHg·min·g ^-1·ml ^-1) fell progressively from 59.37 ± 14.56 before surgery to a nadir of 35.76 ± 10.12 at 6 mo after CABG (P <0.01 vs. preoperatively). The results of the present study confirm that CABG improves coronary vasodilator reserve progressively as a result of reduction in minimal coronary resistance. These data suggest persistent microvascular dysfunction that recovers slowly after surgery.