Border zone geometry increases wall stress after myocardial infarction: contrast echocardiographic assessment

Abstract

After myocardial infarction (MI), the border zone expands chronically, causing ventricular dilatation and congestive heart failure (CHF). In an ovine model ( n = 4) of anteroapical MI that results in CHF, contrast echocardiography was used to image short-axis left ventricular (LV) cross sections and identify border zone myocardium before and after coronary artery ligation. In the border zone at end systole, the LV endocardial curvature ( K) decreased from 0.86 ± 0.33 cm−1 at baseline to 0.35 ± 0.19 cm−1 at 1 h ( P < 0.05), corresponding to a mean decrease of 55%. Also in the border zone, the wall thickness ( h) decreased from 1.14 ± 0.26 cm at baseline to 1.01 ± 0.25 cm at 1 h ( P < 0.05), corresponding to a mean decrease of 11%. By Laplace's law, wall stress is inversely proportional to the product K · h. Therefore, a 55% decrease in K results in a 122% increase in circumferential stress; a 11% decrease in h results in a 12% increase in circumferential stress. These findings indicate that after MI, geometric changes cause increased dynamic wall stress, which likely contributes to border zone expansion and remodeling.