Design and Development of a Torsional Ventricular Assist Device

Congestive heart failure (HF) is a complex disease that remains one of the leading causes of death in the world today, affecting over 5.5 million people in the United States alone and contributing to 1 in every 9 deaths nationwide. Currently, total heart transplantation is considered
the most effective treatment for end stage HF, but there are on average 3000 donor hearts available annually, while there are more than 3500 patients on the transplant waitlist on any given day. For those patients, mechanical circulatory support (MCS), as a bridge-to-transplant (BTT) or more permanent destination therapy (DT), has been employed as an effective alternative for end stage HF patients. However, long-term use of these devices are associated
with life-threatening complications, the most common of which are thromboembolic events triggered by artificial blood-contacting surfaces and hemolysis due to high shear stresses generated by blood flow through MCS devices.
The goal of this research is to develop a torsion-based ventricular assist device (tVAD) to support the failing heart as either a BTT or DT while eliminating the risk of thromboembolic complications common to all cardiac assist devices currently on the market by avoiding blood
contact with artificial surfaces. This approach to cardiac support is inspired by the contractile mechanics of healthy human hearts, which produce a “wringing” motion during systole that allows the ventricles to empty more completely and reduces transmural stresses acting on the heart walls. This dissertation describes: 1) parametric computational simulations used to evaluate the effects of applied apical torsion (AAT) on global cardiovascular hemodynamics to determine optimal design parameters and their effects on regional cardiac biomechanics and determine the
working limitations of such applied torsion therapy; and 2) development of a method for superficial attachment of the tVAD to the epicardium of the heart. Results from the parametric computational simulations representing the most aggressive level of tVAD assist, where the applied rotation angle was 75 degrees and the device coverage
area was 24% up the ventricle (from apex towards the base), yielded increases in left ventricular ejection fraction and stroke work of 49% and 72%, respectively, when compared to a baseline HF model. However, based on the evaluation of regional cardiac biomechanics at the epicardial
and endocardial nodes at the base of the device and the ventricle, applied rotation angles of 65 degrees resulted in large increases in maximum principal strains (ΔE), where all nodes had ΔE ≥0.40, and increases in maximum principal stresses (ΔT), where nearly 75% of the nodes at
ΔT>100 kPa. These results both suggest that supra-physiological levels of AAT could potentially cause damage to the myocardium. Additionally, results of lap-shear tests for the adhesion energies of candidate surgical adhesives suggest that the 316L stainless steel bonded
with an octyl/butyl cyanoacrylate bioadhesive has the potential to secure the tVAD to the epicardium as it actuates on the heart.