Differences in the changing trends of monophasic action potential duration and effective refractory period of the ventricular myocardium after myocardial infarction in vivo

Background The relationship between monophasic action potential duration (MAPD) and effective refractory period (ERP) is poorly understood after myocardial infarction (MI) in vivo. Methods and Results Forty rabbits were randomized into either a sham operation (SO) group (n = 10) or MI group (n = 30). both of which underwent thoracotomy, but the left anterior descending coronary artery was occluded in the MI group only. The MAPD and ERP of the endocardial, midmyocardial and epicardial cells of the infarction zone were observed at baseline, 2 days after thoracotomy and then 5 min, 15 min, 30 min, 2 days, 14 days and 60 days after coronary occlusion (CO). At baseline, ERP correlated strongly with MAPD(90). During the 5-30 min after CO, both MAPD(90) and ERP of the 3 layers of the myocardium shortened markedly (eg, MAPD(90 Mid) was approximately 50% of the baseline value at 5 min after CO). MAPD(90) and ERP recovered gradually over the 2-60 days after MI. ERPMid exceeded MAPD(90) (Mid) and the post repolarization refractoriness phenomenon appeared during the 5-30 min after CO. Conclusions The different changing trends of the MAPD and ERP of the mid-myocardial cells may underlie the arrhythmias that occur after MI.