Objective: 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.
Methods: 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 µg 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 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). Conclusions: 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.
Key words:
Coronary Arteries - Ischemia - Reperfusion - Vasoconstriction
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1 Presented at the 3rd Joint Meeting of the German, Austrian and Swiss Societies for
Thoracic and Cardiovascular Surgery, Lucerne, February 9 - 12, 2000
Gerhard A. Kalweit, MD
Department of Thoracic and Cardiovascular Surgery Heinrich-Heine-University
Moorenstraße 5
40225 Düsseldorf
Germany
Phone: + 49 (211) 811-8331
Fax: + 49 (211) 811-8333
