Intracoronary versus intravenous nitroglycerin on the transmural distribution of coronary blood flow

The effect of intracoronary versus intravenous administration of nitroglycerin (GTN) on the transmural distribution of coronary blood flow (epi/endo) was studied in an isolated canine heart preparation and intact dogs. The distribution of blood flow between epicardium and endocardium of the left ventricle was determined by use of radioactive microspheres (15 micrometer diameter). Intracoronary infusion of GTN in the isolated heart significantly increased epi/endo during a constant coronary blood flow, whereas no change in epi/endo was observed during a constant coronary perfusion pressure. When maximal coronary vasodilatation was produced by chromonar, the epi/endo increased significantly, however intracoronary GTN produced no further vasodilatation and did not improve epi/endo. In contrast, intravenous infusion of GTN in intact hearts significantly decreased epi/endo. These results suggest that intracoronary GTN does not enhance endocardial perfusion and may even produce a coronary steal, whereas intravenous GTN may improve endocardial perfusion via indirect haemodynamic actions.