Effects of metoprolol on atrial remodeling in rats with acute myocardial infarction

Objective:This study was to investigate whether metoprolol,a β1-blocker can improve atrial remodeling in rats after acute myocardial infarction(MI).Methods:12 rats underwent left coronary artery ligation and were randomized into MI group(MI group,n=6) and metoprlol treatment group(MI+M group,n=6) in which metoprolol was given orally at 10 mg·kg-1·d-1.Another sham operated group(Sham group,n=6) served as controls.After 28-day observation period,echocardiography,ECG and invasive electrophysiology were performed.Results:Twenty-eight days after MI,infarcted rats demonstrated dilated left ventricle and atrium as evidenced by increases in left ventricular end-diastolic dimension(LVEDD),left atrial diameter(LAD) and lower fractional shortening(FS) compared with sham operated rats(P0.05,respectively).The structural changes in MI group were associated with longer maximal P wave duration(Pmax) and dispersion(Pd) compared with Sham group(P0.05,respectively).Furthermore,shortened AERP and its impaired rate-adaptation in MI group(P0.05,vs.Sham group,respectively) led to increased incidence of atrial arrhythmias,including atrial fibrillation and flutter,which were induced by either atrial overdrive pacing or programmed stimulation,when compared with that in Sham group(P0.05).Metoprolol not only resulted in reversal of LVEDD and LAD in MI rats,but also significantly improved rate-adaptation of AERP which in turn decreased the incidence of atrial arrhythmias(P0.05,respectively).Conclusion:Atrial structural and electrical remodeling in rats after acute MI can be attenuated by metoprolol,which is associated with lower incidence of atrial arrhythymias after MI.