Magnetic retrieval of prosthetic heart valves for redo-TAVI

Abstract

With increasing life expectancy and the low durability of bioprosthetic valve replacements, the number of patients requiring multiple redo aortic valve replacements are on the rise. For patients unable to undergo open heart surgery, the only current option for redo valve replacement is the Valve-in-Valve (ViV) method which minimally invasively deploys a new prosthetic inside the failed one. The number of ViV procedures a patient can undergo are limited due to the shrinking of the aortic annulus with each additional prosthesis as smaller aortic annuli result in a larger reduction of blood pressure across the valve, decreasing blood output to the body. To alleviate this problem, a novel prosthetic valve system, e-TAVI, was designed that allowed for the removal of the degenerated valve prosthesis and the deployment of a new one minimally invasively. The e-TAVI system comprises a three component system: (i) a holding member anchored inside the aortic root; (ii) an exchangeable valve that could be engaged to and disengaged from this holding member via (iii) a dedicated catheter. The method of engagement between the components incorporated ferromagnetic regions on the exchangeable valve and electromagnets in the catheter. The three components were designed and modelled computationally and simulations were performed to assess crimping, deployment, engagement, and removal of an exchangeable valve. The crimping of the exchangeable valve frame via the catheter electromagnets resulted in the radially inward crushing of the frame forming a star-shaped axial profile. The force required to reduce the diameter of the frame in this manner was lower than its outward radial force, demonstrating an advantageous trade-off for the exchangeable valve frame design. Larger ferromagnetic regions, wider struts and shorter cell height on the frame resulted in larger removal force requirements. Smaller ferromagnetic regions and smaller catheter electromagnets resulted in a higher required current through the catheter to achieve this required force. The re-sheathing of the exchangeable valve following crimping via the catheter electromagnets was not possible with contact between the electromagnets and ferromagnetic regions being unable to resist the shear force. This showed the need for an additional mechanical engagement between the catheter and the exchangeable frame to achieve full retrieval of the exchangeable valve in the e-TAVI system.

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Identifiers

ORCID for Oguz Can Eren: orcid.org/0000-0002-2665-3611

ORCID for Nicholas Curzen: orcid.org/0000-0001-9651-7829

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