Abstract:
The Acorn CorCap Cardiac Support Device (CSD) is a woven polyester jacket designed for patients with dilated cardiomyopathy, aiming to reverse progressive ventricular remodeling. Despite its clinical use, the precise biomechanical effects of the Acorn CSD on myofiber stress and global ventricular function have remained largely unquantified. This study sought to address this critical gap, testing the hypothesis that the Acorn CSD reduces end-diastolic (ED) myofiber stress within the failing myocardium, as understanding these mechanical interactions is crucial for optimizing the device's design and application. To biomechanically investigate the device's impact, a previously developed, weakly coupled biventricular finite element (FE) model of the heart was employed, integrated with a lumped-parameter circulatory system model. This comprehensive model was constructed using magnetic resonance images obtained from a canine model with pacing tachycardia-induced dilated cardiomyopathy, providing a realistic anatomical and physiological basis for the simulations. Virtual applications of the CSD were simulated under various conditions, including the CSD alone, with a rotated fabric fiber orientation, with a 5% prestretch, and wrapped exclusively around the left ventricle (LV-only case). For each scenario, the biomechanical effects on myofiber stress at end-diastole and overall cardiac pump function were meticulously calculated. The material properties of the heart were modeled using nearly incompressible, transversely isotropic, hyperelastic constitutive laws for passive and active myocardium, and the CSD fabric itself was modeled using a derived material property law, describing its behavior as an open-cell mesh with specific fiber orientations. The biomechanical simulations revealed that the Acorn CSD significantly impacts ED myofiber stress, particularly in the left ventricular free wall, demonstrating substantial reductions. However, these beneficial reductions in myocardial stress were accompanied by a biomechanical tradeoff: the Acorn CSD consistently reduced stroke volume at a left ventricular end-diastolic pressure, indicating a direct influence on pump function. Notably, the CSD wrapped only around the left ventricle resulted in a modest stress reduction but with minimal negative impact on overall pump function. The study also observed that stress within the CSD fabric was substantially higher than in the myocardium itself, highlighting the load-sharing role of the device, and the application of the CSD also led to a leftward shift in the end-diastolic pressure-volume relationship (EDPVR) for both ventricles, indicating a reduction in diastolic compliance. This biomechanical modeling study definitively demonstrates that the Acorn CSD significantly reduces ED myofiber stress, a key factor in mitigating adverse ventricular remodeling. However, the findings underscore a critical design consideration: applying the CSD exclusively to the left ventricle appears to be the only configuration that achieves this substantial stress reduction with minimal detrimental effects on the heart's overall pump function. The results strongly suggest that further optimization of the LV-only CSD design and its fabric orientation is crucial to maximize myofiber stress reduction while minimizing any negative impact on cardiac pump function, paving the way for more biomechanically effective cardiac support devices.
