Nitrates in Acute Myocardial Infarction

Summary

Nitrates relieve symptoms and improve left ventricular haemodynamics during acute myocardial ischaemia. The ability to increase cardiac output appears to be greatest in those patients with the most severe left ventricular failure. In humans and in animal experiments it has been demonstrated that indices of infarct evolution are reduced by early (<6 hours) administration of nitrate. Glyceryl trinitrate reduces myocardial oxygen consumption and improves delivery of oxygen to the ischaemic subendocardium. In addition, nitrates dilate epicardial coronary vessels with improvement of collateral flow. Glyceryl trinitrate appears to have a more favourable effect on coronary collateral flow, pulmonary artery pressure, myocardial oxygen consumption and lactate production than other vasodilators. The effect of glyceryl trinitrate is dose dependent; doses larger than 100μg/min may cause a paradoxical increase in the ischaemic condition. Hypovolaemic patients or patients with right heart infarction seem especially susceptible to hypotension. Nitrate-induced hypotension occurs in 15 to 20% of all patients with acute myocardial infarction.

Administration of glyceryl trinitrate appears to offer most benefit in acute myocardial infarction complicated by significant left ventricular dysfunction. There is evidence that morbidity and mortality are reduced by early administration of nitrates; however, a properly conducted randomised double-blind trial remains to be performed.