LONG-TERM EFFECTS OF BETA-ADRENERGIC BLOCKING-AGENT TREATMENT ON HEMODYNAMIC FUNCTION AND LEFT-VENTRICULAR REMODELING IN RATS WITH EXPERIMENTAL MYOCARDIAL-INFARCTION - IMPORTANCE OF TINTING OF TREATMENT AND INFARCT SIZE

Objectives. This study was designed to assess the long-term effects of a beta(1)-selective beta-adrenergic blocking agent on mortality, in v iva hemodynamic function, left ventricular volume and wall stress in p ost-myocardial infarction (MI) rats, Background. Beta-blockers have sh own beneficial results in clinical studies after MI, However, the unde rlying mechanism is not yet understood, and experimental studies have shown conflicting results, Methods. Bisoprolol (60 mg/kg body weight p er day) was given 30 min or 14 days after MI or sham operation, Result s, The mortality rate was reduced only In early bisoprolol-treated rat s (29% vs. 46% in untreated rats, p < 0.05), Heart rate was equally re duced in all treatment groups, and the maximal rate of rise of left ve ntricular systolic pressure (dP/dt(max)) decreased in sham rats and in rats with a small to moderate infarct size, Stroke volume index was u nchanged in sham rats and in rats with a small to moderate infarct wit h early or late bisoprolol treatment and increased in rats with a larg e infarct in the late bisoprolol group, Left ventricular volume was in creased by bisoprolal in sham rats and rats with a small infarct but n ot in rats with a large infarct, Conclusions. Treatments starting earl y (30 min) or late (14 days) after coronary artery ligation with bisop rolol increased left ventricular volume in sham rats and in rats dth a small infarct but not in rats with a large infarct, Late bisoprolol t reatment improved stroke volume index, and early bisoprolol treatment reduced diastolic wall stress, in rats with a large myocardial infarct . Thus, bisoprolol effects on remodeling and cardiac performance after myocardial infarction strongly depend on infarct size and timing of t reatment, This finding mag explain previous controversial results that did not consider infarct size and timing of treatment. (C) 1998 by th e American College of Cardiology.