Effect Of Acute Myocardial Ischemia And Early Reperfusion On Global Repolarization And Dispersion Of The Left Ventricular Epicardium In Vivo In Swines

Objective:To investigate the effect of acute myocardial ischemia and early reperfusion on global repolarization and dispersion of the left ventricular epicardium in swines in order to evaluate the possible substrate of malignant ventricular arrhythmias after acute myocardial ischemia and early reperfusion.Methods:Monophasic action potentials (MAPs) were recorded from left ventricular epicardial sites before and after legating the left anterior descending coronary artery for 30min, 120min and after reperfusion for 10min in 9 healthy swines by using the CARTO electroanatomic mapping system. Local activation time (AT), end of repolarization time (EORT) and MAP duration (MAPD) were calculated and analyzed in each site and 3-dimensional global maps of AT, EORT and MAPD were constructed before and after acute cardiac ischemia and reperfusion. Some definitions to this test: Activation Time (AT), time from the earliest activation of the ventricle to that of the local depolarization. End Of Repolarization Time (EORT), time from the earliest activation of the ventricle to the end of repolarization. Monophasic Action Potential Duration (MAPD), time from the local depolarization of the ventricle to the end of repolarization. Dispersion of ventricular repolarization (DVR), EORT_max-EORT_min.Results:(1) In normal state, the EORT sequence clearly followed the sequence of activation, the longest MAPs were recorded in or close to the earliest activation area, and the shortest were recorded in or close to the latest activation area in all the swine maps. MAPD and AT were negatively correlated, while EORT and AT were positively correlated in all maps, accordingly the global dispersion of repolarization was relatively small. (2)At the time of 30 min and 120min after acute myocardial ischemia, the negative correlation between AT and MAPD disappeared. AT delayed and MAPD significantly shortened in ischemic zones, but both AT and MAPD had not obviously altered in non-ischemic zones, so that the global repolarization dispersion of ventricular epicardium increased significantly (P<0.01). (3)After early reperfusion for 10min, although AT partially recovered, MAPD remained decreased, the negative correlation between AT and MAPD disappeared, and the global repolarization dispersion of left ventricular epicardium was not recovered.Conclusions: Repolarization gradients exist over the swine left ventricular epicardium in normal state. The activation sequence is a determinant for the repolarization sequence. The delayed AT and shortened MAPD might be very important in significantly increasing the global dispersion of ventricular epicardial repolarization during acute ischemia, and the global dispersion of ventricular epicardial repolarization was not recovered after reperfusion, in favor of the frequent occurrences of malignant ventricular arrhythmias after acute ischemia and early reper- fusion.