Evaluation of the effects of systemic nitroglycerin on perfusion of ischemic myocardium in coronary heart disease assessed intraoperatively by antegrade blood flow through intact saphenous vein bypass grafts.

To evaluate systemic nitroglycerin (NTG) effects on reduced perfusion of ischemic myocardium in coronary disease, intravenous NTG actions on coronary circulatory dynamics were directly assessed intraoperatively during aortocoronary bypass surgery in 24 patients. Thus metered antegrade blood flow was measured through 56 separate intack saphenous vein bypass grafts to analyze NTG perfusion response in the obstructed native coronary artery (CA). In 34 bypassed CA with proximal luminal diameter narrowing greater than 50% to 90%, NTG reduced (p less than 0.01) graft flow (GF) 82 to 63 cc/min, thereby indicating that NTG dilated proximal stenoses with resultant increased CA flow. In 11 bypassed CA obstructed greater than 90% to 100% with well developed collaterals distally, NTG decreased (p less than 0.05) GF 64 to 53 cc/min, thus indicating enhanced collateral flow. In contrast, in 11 bypassed CA obstructions greater than 90% to 100% without collaterals, that NTG increased (p less than 0.02) GF 91 to 100 cc/min indicated NTG nonresponsiveness of the severely diseased CA. Thus systemic NTG improves perfusion to ischemic myocardium subserved by diseased coronaries with less than 90% stenosis or by greater than 90% obstructed vessels with substantial collaterals distally.