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Research Papers

Self-Expanding Stent and Delivery System for Aortic Valve Replacement

[+] Author and Article Information
Dumitru Mazilu

e-mail: mazilud@nhlbi.nih.gov

Ming Li

e-mail: lim2@nhlbi.nih.gov
Cardiothoracic Surgery Research Program,
National Institutes of Health/National Heart,
Lung, and Blood Institute,
10 Center Drive, MSC 1550,
Bldg 10, Room B1D47,
Bethesda, MD 20892

Ozgur Kocaturk

Cardiovascular Intervention Program,
National Institutes of Health/National Heart,
Lung, and Blood Institute,
10 Center Drive, MSC 1550,
Bldg 10, Room B1D47,
Bethesda, MD 20892
e-mail: kocaturko@nhlbi.nih.gov

Keith A. Horvath

Cardiothoracic Surgery Research Program
National Institutes of Health/National Heart,
Lung, and Blood Institute,
10 Center Drive, MSC 1550,
Bldg 10, Room B1D47,
Bethesda, MD 20892
e-mail: horvathka@nhlbi.nih.gov

1Corresponding author.

Manuscript received April 4, 2012; final manuscript received September 14, 2012; published online November 1, 2012. Assoc. Editor: James Moore.

J. Med. Devices 6(4), 041006 (Nov 01, 2012) (9 pages) doi:10.1115/1.4007750 History: Received April 04, 2012; Revised September 14, 2012

Currently, aortic valve replacement procedures require a sternotomy and use of cardiopulmonary bypass (CPB) to arrest the heart and provide a bloodless field in which to operate. A less invasive alternative to open heart surgery is transapical or transcatheter aortic valve replacement (TAVR), already emerging as a feasible treatment for patients with high surgical risk. The bioprosthetic valves are delivered via catheters using transarterial or transapical approaches and are implanted within diseased aortic valves. This paper reports the development of a new self-expanding stent for minimally invasive aortic valve replacement and its delivery device for the transapical approach under real-time magnetic resonance imaging (MRI) guidance. Made of nitinol, the new stent is designed to implant and embed a commercially available bioprosthetic aortic valve in aortic root. An MRI passive marker was affixed onto the stent and an MRI active marker to the delivery device. These capabilities were tested in ex vivo and in vivo experiments. Radial resistive force, chronic outward force, and the integrity of bioprosthesis on stent were measured through custom design dedicated test equipment. In vivo experimental evaluation was done using a porcine large animal model. Both ex vivo and in vivo experiment results indicate that the self-expanding stent provides adequate reinforcement of the bioprosthetic aortic valve and it is easier to implant the valve in the correct position. The orientation and positioning of the implanted valve is more precise and predictable with the help of the passive marker on stent and the active marker on delivery device. The new self-expanding nitinol stent was designed to exert a constant radial force and, therefore, a better fixation of the prosthesis in the aorta, which would result in better preservation of long-term heart function. The passive marker affixed on the stent and active marker embedded in the delivery devices helps to achieve precise orientation and positioning of the stent under MRI guidance. The design allows the stent to be retracted in the delivery device with a snaring catheter if necessary. Histopathology reports reveal that the stent is biocompatible and fully functional. All the stented bioprosthesis appeared to be properly seated in the aortic root.

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© 2012 by ASME
Topics: Valves , stents , Prostheses
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Figures

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Fig. 1

(a) Self- expanding stent; (b) bioprosthetic valve affixed in self-expanding stent

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Fig. 2

Unfolded geometry with technical details of the stent

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Fig. 3

The bioprosthesis delivery systems with loop coil antenna

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Fig. 4

Device for radial force measurement

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Fig. 5

(a) Chronic outward force (curve 2) and radial resistive force (curve 1) for stent alone; (b) resistive force (curve 3) and chronic outward force (curve 4) for stent and Toronto SPV, St. Jude valve mounted together

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Fig. 6

A 25 mm modified Freestyle, Medtronic valve is presented mounted in a 26 mm stent before crimping and after crimping at 10 mm diameter

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Fig. 7

Image artifacts of the stainless steel marker on the stent under MRI. (a) Transversal section; (b) long axis section.

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Fig. 8

Self-expanding stented prosthesis deployment. (a) Stented prosthesis in delivery device, (b) stented prosthesis partially deployed, (c) stented prosthesis fully deployed.

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Fig. 9

Radiographs of the heart taken from anterior (a) and lateral (b)

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Fig. 10

The histopathology results at the proximal most end of the device. (a) Proximal section of the prosthetic valve; (b) high power view of the inferior edge of the device; (c) higher magnification of a boxed area in (a); (d) higher magnification of the superficial region of the skirt fabric bundles and surrounding chronic inflammation.

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Fig. 11

The histopathology results at the most distal section of the prosthetic valve. (a) Distal section of the prosthetic valve; (b) mild neointimal tissue completely covering the stent struts; (c) is high power view of the stent strut from (b).

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