Intravenous Metoprolol Preceding Thrombolysis in Acute Thrombotic Myocardial Infarction in the Dog; Effects on Infarct Size, Myocardial Blood Flow, and Left Ventricular Function

Intravenous (i.v.) metoprolol preceding thrombolysis in an anesthetized dog model of thrombotic occlusion of the anterior descending coronary artery helps limit infarct size (IS). We wished to determine whether these effects are caused at least in part by enhancement of collateral blood flow to the area at risk (AAR). Thrombotic occlusion was provoked by a copper-coil technique. We measured intracardiac pressures and their derivatives by catheter-tip micromanometers, cardiac output (CO) by thermodilution method, regional myocardial blood flow (RMBF) by radioactive microspheres technique, global and regional left ventricular (LV) function by ventriculography, and IS with triphenyltetrazolium at the end of the experiment. Measurements were performed before and after 60-min occlusion and after 30- and 90-min reperfusion. Received fifteen minutes after occlusion, 12 dogs metoprolol 0.3 mg/kg i.v. followed by 0.3 mg/kg/h; 12 received saline. Thrombolysis was performed in all dogs after 60-min occlusion with recombinant tissue-type plasminogen activator (rt-PA) 10 micrograms/kg/min for 30 min. Hemodynamic findings were similar in both groups. During occlusion, collateral flow to total AAR (18.6 +/- 7.5 vs. 11.0 +/- 6.1 ml/min/100 g), to its subepicardial (22.1 +/- 8.1 vs. 12.2 +/- 7.2 ml/min/100 g), midmyocardial (16.0 +/- 8.9 vs. 8.0 +/- 5.5 ml/min/100 g), and endocardial (14.1 +/- 8.1 vs. 7.3 +/- 6.0 ml/min/100 g) layers was higher (p < or = 0.03) in metoprolol than in placebo-treated dogs.(ABSTRACT TRUNCATED AT 250 WORDS)