Reversal by phenylephrine of the beneficial effects of intravenous nitroglycerin in patients with acute myocardial infarction.

Nitroglycerin has been shown to reduce ST-segment elevation during acute myocardial infarction, an effect potentiated in the dog by agents that reverse nitroglycerin-induced hypotension. Our study was designed to determine the effects of combined nitroglycerin and phenylephrine therapy. Ten patients with acute transmural myocardial infarctions received intravenous nitroglycerin, sufficient to reduce mean arterial pressure from 107 +/- 6 to 85 +/- 6 mm Hg (P less than 0.001), for 60 minutes. Left ventricular filling pressure decreased from 19 +/- 2 to 11 +/- 2 mm Hg (P less than 0.001). SigmaST, the sum of ST-segment elevations in 16 precordial leads, decreased (P less than 0.02) with intravenous nitroglycerin. Subsequent addition of phenylephrine infusion, sufficient to re-elevate mean arterial pressure to 106 +/- 4 mm Hg (P less than 0.001) for 30 minutes, increased left ventricular filling pressure to 17 +/- 2 mm Hg (P less than 0.05) and also significantly increased sigmaST (P less than 0.05). Our results suggest that addition of phenylephrine to nitroglycerin is not beneficial in the treatment of patients with acute myocardial infarction.