Early and late remodeling of the left ventricle after acute myocardial infarction

Abstract

This report describes early and later structural changes that occur in infarcted and noninfarcted ventricular myocardium after coronary arterial ligation in the rat. Histologic analysis was conducted of hearts subjected to 2 days (n = 22) and 21 days (n = 22) of coronary arterial occlusion, or to a sham operation (n = 22). Lengths, circumferences and areas of the left ventricle, of infarcted myocardium and of noninfarcted myocardium were obtained by videoplanimetry. Although the left ventricular (LV) endocardial circumference was similarly increased at 2 days (19 ± 3 mm, mean ± standard deviation) and 21 days (20 ± 3 mm) compared with shams (13 ± 3 mm, p <0.01), LV epicardial circumference was similar in all 3 groups (30 ± 2, 31 ± 2 and 31 ± 2 mm, respectively). The area enclosed by the endocardial circumference was significantly (p <0.01) increased at 2 days (20 ± 6 mm 2) and 21 days (22 ± 6 mm 2) compared with shams (7 ± 4 mm 2); however, the area enclosed by the epicardial circumference was similar at 2 days, 21 days and in shams (70 ± 9, 72 ± 9 and 73 ± 10 mm 2, respectively). The total LV tissue area was similar at 2 and 21 days, but was less than that in shams (p <0.01). Between 2 and 21 days, 3 measures of infarcted myocardium significantly decreased: its segments of endocardial and epicardial circumference, its circumference and its area. Between 2 and 21 days, 4 measures of noninfarcted myocardium significantly increased: septal length, LV free wall length, right ventricular length and area. Therefore, early (within 2 days) structural changes after acute myocardial infarction consist of LV tissue loss, presumably along the infarcted subendocardium, concomitant with LV cavity dilation; later (between 2 and 21 days) changes consist of contraction of infarcted tissue with compensatory expansion (hypertrophy) of noninfarcted tissue.