Biventricular finite element modeling of the Acorn CorCap Cardiac Support Device on a failing heart

Abstract

Background: The Acorn CorCap Cardiac Support Device (CSD; Acorn Cardiovascular Inc, St. Paul, MN) is a woven polyester jacket that is placed around the heart and designed to reverse the progressive remodeling associated with dilated cardiomyopathy. However, the effects of the Acorn CSD on myofiber stress and ventricular function remain unknown. We tested the hypothesis that the Acorn CSD reduces end-diastolic (ED) myofiber stress.

Methods: A previously described weakly coupled biventricular finite element (FE) model and circulatory model based on magnetic resonance images of a dog with dilated cardiomyopathy was used. Virtual applications of the CSD alone (Acorn), CSD with rotated fabric fiber orientation (rotated), CSD with 5% prestretch (tight), and CSD wrapped only around the left ventricle (LV; LV-only) were performed, and the effect on myofiber stress at ED and pump function was calculated.

Results: The Acorn CSD has a large effect on ED myofiber stress in the LV free wall, with reductions of 55%, 79%, 92%, and 40% in the Acorn, rotated, tight, and LV-only cases, respectively. However, there is a tradeoff in which the Acorn CSD reduces stroke volume at LV end-diastolic pressure of 8 mm Hg by 23%, 25%, 30%, and 7%, respectively, in the Acorn, rotated, tight, and LV-only cases.

Conclusions: The Acorn CSD significantly reduces ED myofiber stress. However, CSD wrapped only around the LV was the only case with minimal negative effect on pump function. Findings suggest that LV-only CSD and Acorn fabric orientation should be optimized to allow maximal myofiber stress reduction with minimal reduction in pump function.

Fig. 1

(A) The biventricular finite element model shows the left ventricle in red and the right ventricle in blue. The yellow lines indicate the edges that were fully constrained. (B) The green shell elements represent the Acorn cardiac support device jacket. The contour lines inside of the green shell elements represent the boundaries of the ventricular cavities, and the white lines on the outer shell surface show an example of the fiber orientations.

Fig. 2

(A) Effect of the Acorn cardiac support device (CSD), an Acorn with 5% (tight Acorn,) and an Acorn applied only to the left ventricle (LV Only) on end-systolic (ESPVR) end-diastolic pressure-volume relationship (EDPVR). The tight Acorn had the greatest effect, whereas the LV-only case has the least effect on LV EDPVR. The ESPVR was not changed by Acorn application. (B) Effect of the Acorn CSD fabric orientation on LV EDPVR. Fabric orientation had minimal effect.

Fig. 3

Effect of the Acorn cardiac support device, an Acorn with 5% prestretch (tight Acorn) and an Acorn applied only to the left ventricle (LV only) on right ventricular (RV) end-diastolic (EDPVR) and end-systolic pressure-volume relationship (ESPVR). The tight Acorn had the greatest effect, whereas the LV- only case had the least effect on RV EDPVR. The ESPVR was not changed by Acorn application.

Fig. 4

(A) Effect of the Acorn cardiac support device (CSD), an Acorn with 5% (tight Acorn) and an Acorn applied only to the left ventricle (LV only) on Starling’s law. Tight Acorn had the greatest effect, whereas the LV-only case has the least effect on LV end-diastolic (ED) pressure-volume relationship. (B) Effect of the Acorn CSD fabric orientation on Starling’s law. Fabric orientation had minimal effect.