Role of nitrates in acute myocardial infarction

In patients with acute myocardial infarction, intravenous nitroglycerin lowers left ventricular filling pressure and systemic vascular resistance. At lower infusion rates (less than 50 micrograms/min) nitroglycerin is principally a venodilator, whereas at higher infusion rates more balanced venous and arterial dilating effects are seen. Patients with left ventricular failure demonstrate increased or maintained stroke volumes, whereas patients without failure show a decrease in stroke volume. All hemodynamic subgroups show a decrease in left ventricular filling pressures and a reduction in electrocardiographic evidence of regional myocardial ischemia. Longer-term infusions (24-48 hours) have been shown to result in myocardial preservation, as assessed by global and regional left ventricular function and laboratory indices of infarct size. Comparison of intravenous nitroglycerin and sodium nitroprusside reveals increased intercoronary collateral flow with nitroglycerin, in contrast to a decrease with nitroprusside, compatible with a "coronary steal." Short-term administration of intravenous nitroglycerin with or without chronic administration of long-acting nitrates have been found both to reduce short-term mortality and to have long-term beneficial effects on left ventricular remodeling in patients with anterior transmural infarctions. Current clinical practice would utilize intravenous nitroglycerin as initial therapy for patients receiving intravenous thrombolytic therapy and/or acute percutaneous transluminal coronary angioplasty within 4-6 hours of the onset of symptoms of acute myocardial infarction, in order to optimize intercoronary collateral flow until reperfusion can be accomplished. Patients reaching the hospital greater than 6 hours but less than 14 hours after symptom onset can still benefit from intravenous nitroglycerin for 24-48 hours.(ABSTRACT TRUNCATED AT 250 WORDS)