Patient-specific finite element-based analysis of ventricular myofiber stress after Coapsys: importance of residual stress

Background: We sought to determine regional myofiber stress after Coapsys device (Myocor, Inc, Maple Grove, MN) implantation using a finite element model of the left ventricle (LV). Chronic ischemic mitral regurgitation is caused by LV remodeling after posterolateral myocardial infarction. The Coapsys device consists of a single trans-LV chord placed below the mitral valve such that when tensioned it alters LV shape and decreases chronic ischemic mitral regurgitation. Methods: Finite element models of the LV were based on magnetic resonance images obtained before (preoperatively) and after (postoperatively) coronary artery bypass grafting with Coapsys implantation in a single patient. To determine the effect of Coapsys and LV before stress, virtual Coapsys was performed on the preoperative model. Diastolic and systolic material variables in the preoperative, postoperative, and virtual Coapsys models were adjusted so that model LV volume agreed with magnetic resonance imaging data. Chronic ischemic mitral regurgitation was abolished in the postoperative models. In each case, myofiber stress and pump function were calculated. Results: Both postoperative and virtual Coapsys models shifted end-systolic and end-diastolic pressure-volume relationships to the left. As a consequence and because chronic ischemic mitral regurgitation was reduced after Coapsys, pump function was unchanged. Coapsys decreased myofiber stress at end-diastole and end-systole in both the remote and infarct regions of the myocardium. However, knowledge of Coapsys and LV prestress was necessary for accurate calculation of LV myofiber stress, especially in the remote zone. Conclusions: Coapsys decreases myofiber stress at end-diastole and end-systole. The improvement in myofiber stress may contribute to the long-term effect of Coapsys on LV remodeling. © 2012 The Society of Thoracic Surgeons.