806-1 Left Ventricular Ejection Fraction After Myocardial Infarction: Importance of Both Infarct Site and Size

Left ventricular ejection fraction (LVEF) is an important prognostic variable after myocardial infarction (MI). While the extent of MI is known to affect the subsequent global LVEF, it is not clear whether anatomical site per se affects LVEF. Therefore, 48 consecutive patients (pts) who did not receive lytic therapy or undergo early revascularization were studied byechocardiography one week after Q wave MI. Using a previously validated endocardial mapping technique, the size of abnormal wall motion (AWM) in relation to the total endocardial surface area and the site of AWM were quantitated, LVEF was measured by Simpson's method using 2 apical views.ResultsNineteen pts had anterior MI (ANT) and 29 had inferior MI (INF). The mean LVEF was similar in both groups (ANT 46.9±14.7% vs INF 51.7±9.4%, pNS). The mean %AWM was greater in ANT MI (29.7±14.5) than in INF MI (21.3±13.8) (p=0.05). After accounting for differences in infarct size by multivariate regression analysis, both infarct size (p=0.0001) and infarct site (p=0.007) were significant independent determinants of LVEF. This effect was most pronounced in larger ANT Mis (%AWM>25%) where the LVEF was significantly lower than in smaller Mis. In INF MI, despite a similar range of sizes. increasing %AWM had minimal effect on LVEF.ConclusionIn addition to infarct size, the site of AWM is an important determinant of global LVEF. This observation may reflect site-dependent differences in the biomechanical responses to regional ventricular dysfunction