[Effect of metoprolol on ventricular relaxation in experimental myocardial infarction]

During the initial phases of myocardial infarction the relaxation ventricular time increases. To assess the effect of metoprolol, a beta-blocker agent, on constant T, an index derived from left ventricular pressure during the isovolumic relaxation phase, 12 mongrel dogs underwent surgical ligation of the anterior descending coronary artery. Constant T, diastolic ventricular pressure, heart rate and mean arterial pressure were measured at control and after 15, 30, 60, 120 and 180 minutes after arterial occlusion. Six dogs were used as controls while the other six received 35 mg/kg/min of methoprolol, infused during 5 minutes. Untreated dogs had longer T times, higher ventricular filling pressures and hypotension at the end of the study in comparison with the treated does, who maintained diastolic function and did not show important changes of arterial pressure. The beta-blocker decreased the abnormality of relaxation time and preserved ventricular filling and systemic pressures in this model of experimental infarction.