Effect of nitrate infusions on the systemic and coronary circulations following acute experimental myocardial infarction in the intact dog

To determine the systemic and the coronary effects of nitrates in acute myocardial infarction, 3 groups of anesthetized closed chest dogs were studied. In a group of normal dogs an hour-long intravenous infusion of isosorbide dinitrate was administered. In a second group a small infarct of the myocardium was produced by catheter wedging in a small coronary side branch. In the third group occlusion of a branch of the main left coronary artery was produced by a thrombus-forming catheter electrode. Isosorbide dinitrate infusion in normal dogs caused reductions in aortic pressure, left ventricular end-diastolic pressure and cardiac output and work. Coronary resistance was reduced only at 5 minutes of infusion. Systemic effects of isosorbide dinitrate were similar in the 2 groups with infarction. Mild hypotension (average 10 mm Hg) did not provoke ventricular arrhythmias. Unlike the cardiac output in normal dogs, this value tended to rise rather than fall and left ventricular work was unchanged. The dogs with catheter wedging showed a significant increase in coronary collateral flow and a decrease in resistance. Narrowing of the coronary arteriovenous oxygen difference occurred in the dogs with wedging and thrombus formation. In the absence of cardiogenic shock nitrates may be safely administered to dogs with acute experimental myocardial infarction and may result in enhanced collateral coronary flow and reduction in oxygen requirements of the heart.