Effects of isoproterenol on hemodynamic alterations, myocardial metabolism, and coronary flow in experimental acute myocardial infarction with shock

Abstract Hemodynamic and cardiac metabolic effects were investigated in dogs given isoproterenol (2 to 6.6 μg per minute) and in those receiving no therapy, following production of acute myocardial infarction with shock by plastic sphere coronary embolization. Following coronary embolization, before therapy, there were significant declines in cardiac output, aortic pressure, coronary sinus flow, and left ventricular mechanical efficiency. Left ventricular “excess lactate” was produced in almost all animals. After 15 minutes of isoproterenol infusion, there were slight increases of cardiac output, heart rate, left ventricular work, coronary flow, and left ventricular oxygen consumption. Left atrial and aortic pressures, left ventricular mechanical efficiency, and “excess lactate” production were unchanged. Systemic and coronary vascular resistances declined moderately. With continued infusion, for one hour, cardiac output, aortic pressure, and coronary sinus flow declined to levels obtained prior to infusion and left ventricular “excess lactate” production increased further. There was progressive decline of arterial pH. In comparison to those receiving no therapy, isoproterenol-treated animals had significantly lower systemic and coronary vascular resistances and greater left ventricular “excess lactate” production. It is concluded that isoproterenol produces moderate initial hemodynamic improvement in acute myocardial infarction with shock, but this is not sustained and left ventricular “excess lactate” production is unfavorably affected. It is suggested that lack of significant sustained hemodynamic improvement and continued anaerobic metabolism with isoproterenol therapy in acute myocardial infarction with shock most probably results from failure to raise the critically low coronary perfusion pressure sufficiently to produce adequate oxygenation of the acutely ischemic left ventricle.