Coronary vascular stunning in bypass operations during reperfusion and treatment with nitroglycerin

A compromised blood flow after ischemia and reperfusion caused by an increased coronary artery resistance can additionally jeopardize the recovery of myocytes. During routine bypass operations, we investigated the effect of various nitroglycerin doses on elevated coronary resistance before and after ischemia and after a defined reperfusion period.

46 patients with a low-risk profile scheduled for routine coronary artery bypass grafting were investigated. During normothermic total extracorporeal circulation, the completely relieved and fibrillating heart was completely isolated from the systemic circulation and the coronary artery system was perfused at 300 ml/min and flow-controlled. The perfusion pressures were monitored continuously. This protocol was performed at three time points: I. Control (ctr) = 10 minutes after institution of extracorporeal circulation, II. Early reperfusion (early rep) = immediately after an myocardial ischemia of 46 +/- 8 minutes, and III. Late reperfusion (late rep) = after a reperfusion period of 25 +/- 4.5 minutes. In 12 randomly chosen patients in a second step, 3 microg per kg heart weight per min of nitroglycerin (low-dose NTG) was added to the perfusate at time points I and III. In another 12 patients, we applied a bolus injection of 2 mg into the aortic root instead of low-dose NTG.

Compared to ctr, vascular resistance had decreased at early rep by 17% (0 - 48%) (p < 0.005). At late rep, resistance had increased by 46% (5 - 94%) (p < 0.001) compared to early rep and by 23% (3 - 36%) (p < 0.005) compared to ctr. Resistances had risen in particular in patients with hypertension. Application of low-dose NTG lowered resistances by 5% (0-8%) (non-significant) at ctr, and by 6% (0 - 11%) (non-significant) at late rep. Bolus NTG decreased resistances at ctr by 11% (2 - 21%) (p < 0.05) and at late rep by 21% (6 - 48%) (p < 0.01).

In routine heart surgery, coronary vascular constriction is regularly present during postischemic reperfusion despite myocardial protection measures. NTG abolishes this coronary vascular stunning only in part if systemically applicable dosages are given. High-dose intracoronary application of NTG relieves the coronary vasoconstriction completely, but the dosages needed cannot be applied systemically. In this study, vasoconstriction after reperfusion was markedly increased in patients with hypertension.