Left ventricular rupture threshold during the healing phase after myocardial infarction in the dog

Abstract

The mechanical resistance of the infarcted left ventricle to rupture, or rupture threshold, was measured by the balloon technique 1–42 days after left anterior descending coronary artery ligation in 70 dogs: 26 without infarction (18 sham, 8 with ligation) and 44 with infarction. Rupture threshold in noninfarcted hearts was higher than in infarcted hearts (1168 ± 165 (SD) vs. 754 ± 223 mmHg (1 mmHg = 133.32 Pa), p < 0.001) and did not change over 6 weeks. In contrast, rupture threshold in infarcted hearts decreased (p < 0.05) after 14 days, the average value for 21–42 days being less than that for 1–14 days: 577 ± 140 vs. 867 ± 191 mmHg, p < 0.001. Passive left ventricular stiffness in infarcted hearts was higher than for noninfarcted hearts throughout the 6 weeks during early filling (11.1 ± 3.9 vs. 7.1 ± 1.4 mmHg/mL, p < 0.001) but decreased (p < 0.05) after 14 days during the prerupture phase (11.3 ± 5.3 vs. 6.2 ± 3.0 mmHg/mL, p < 0.005). Between 7 and 42 days, the infarct zone showed marked increase in hydroxyproline (10.0 ± 2.0 vs. 48.8 ± 19.7 mg/g dry weight, p < 0.001), shrinkage (infarct size, 25 ± 9 vs. 9 ± 5% of the left ventricle, p < 0.005), and thinning (infarct to normal wall thickness ratio, 0.83 ± 0.11 vs. 0.51 ± 0.09, p < 0.001) but little further stretching (expansion index or the ratio of lengths of infarcted and noninfarcted segments, 1.14 ± 0.10 vs. 1.28 ± 0.17, p < 0.2). A mild decrease (p < 0.05) in left atrial pressure and increase (p < 0.05) in diastolic area and fractional change in area (two-dimensional echocardiography) were detected at 6 weeks. The late decrease in rupture threshold and prerupture stiffness of the infarcted left ventricle and thinning of the scar suggest a late decrease in mechanical strength and resistance of the infarcted left ventricle to distension.