Effects of continuous nitroglycerin infusion on acute myocardial ischemia in dogs

The effects of a continuous infusion of nitroglycerin (NTG) were evaluated by hemodynamic measurements and measurements of regional myocardial blood flow (RMBF) in dogs on right heart bypass with left anterior descending coronary artery ligation. NTG infusion which decreased afterload, mean aortic pressure (MAP) decreased from 100 to 85 mm Hg, thus also decreasing coronary perfusion pressure) resulted in an 11.8% increase in total coronary blood flow (CBF), a 19.1% decrease in coronary vascular resistance index (CVRI), and a 21.7% decrease in myocardial oxygen consumption (MV?O₂). When MAP was returned to the control level (100 mm Hg) with continuing infusion of NTG, CBF increased 49.1%, and CVRI decreased by 23.4% compared to the pre-NTG ischemic state. Regional myocardial blood flow (microsphere technique) to ischemic tissue at the border of the infarct remained stable with NTG infusion despite decreased MAP, in contrast to the significant fall in RMBF in this region with decreased MAP in the control group without NTG. When MAP was elevated back to pre-NTG levels, an 18.6% increase in RMBF to the border of the infarct was seen compared to an insignificant change in RMBF in untreated (control) animals. These data are consistent with the concept that under conditions of regional myocardial ischemia, coronary blood flow to the “border zone” (ischemic myocardium) is maintained or enhanced by NTG, even when coronary perfusion pressure is modestly reduced.