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

Objective: A compromised blood flow after ischemia and reperfusion caused b y an increased coronary artery resistance can additionally jeopardize the r ecovery of myocytes. During routine bypass operations, we investigated the effect of various nitroglycerin doses on elevated coronary resistance befor e and after ischemia and after a defined reperfusion period. Methods: 46 pa tients with a low-risk profile scheduled for routine coronary artery bypass grafting were investigated. During normothermic total extracorporeal circu lation, the completely relieved and fibrillating heart was completely isola ted from the systemic circulation and the coronary artery system was perfus ed at 300 ml/min and flow-controlled. The perfusion pressures were monitore d continuously. This protocol was performed at three time points: I. Contro l (ctr) = 10 minutes after institution of extracorporeal circulation, II. E arly 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 s tep, 3 mug 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. Results: 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 re p. Bolus NTG decreased resistances at ctr by 11% (2 - 21%) (p < 0.05) and a t late rep by 21% (6 - 48%) (p < 0.01). Conclusions: In routine heart surge ry, coronary vascular constriction is regularly present during postischemic reperfusion despite myocardial protection measures, NTC abolishes this cor onary vascular stunning only in part if systemically applicable dosages are given. High-dose intracoronary application of NTG relieves the coronary va soconstriction completely, but the dosages needed cannot be applied systemi cally. In this study, vasoconstriction after reperfusion was markedly incre ased in patients with hypertension.