FAILURE OF INTRAVENOUS METOPROLOL TO LIMIT ACUTE MYOCARDIAL INFARCT SIZE IN A NONREPERFUSED PORCINE MODEL

The usefulness of intravenous beta-adrenergic receptor blockade in lim iting infarct size when neither reperfusion nor collateral flow occurs is unknown, The effect of intravenous metoprolol on limiting myocardi al infarct size was therefore examined in a nonreperfused porcine mode l, Closed-chest techniques were used to occlude the left anterior desc ending coronary artery, after which animals were randomized at 20 minu tes to receive intravenous metoprolol, 0.75 mg/kg, or placebo, Infarct size examined at 5 hours with Evans blue and triphenyltetrazolium sta ining techniques was expressed as a percentage of total ventricular my ocardium at ischemic risk, This percentage was not significantly diffe rent between the groups (84% +/- 5% with metoprolol vs 90% +/- 4% with placebo; p = 0.4), Myocardial infarct size was not significantly decr eased at 5 hours by early administration of intravenous metoprolol whe n the infarct artery remained occluded and collateral flow was minimal .