Neha Patil (Editor)

Transapical transcatheter mitral valve implantation of the Tiara bio prosthesis

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The Neovasc Tiara is a bioprosthetic mitral valve with a novel transcatheter implantation approach to minimize complications associated with conventional mitral valve replacement or repair. Approximately half of patients with severe symptomatic mitral regurgitation are denied surgery due to factors such as advanced age, co-morbidity, or decreased left ventricular ejection fraction. The less invasive, transapical transcatheter approach used with the Tiara mitral valve may be a promising future alternative. The Tiara mitral valve is currently undergoing human clinical trials, the first of which was successfully performed on January 30, 2014, at St. Paul’s hospital in Vancouver, BC. Since the trials are very recent, the long-term effects of this mitral valve bio-prosthesis in humans are currently unknown.

Contents

Valve Properties

The Tiara consists of a self-expanding metal alloy frame with three bovine pericardial tissue leaflets. The leaflets are cross-linked and mounted on the frame, which is then crimped onto a 32F flexible catheter for implantation. The complex, asymmetrical anatomical structure of the mitral valve poses a challenge for prosthetic mitral valve fabrication. The Tiara’s D-shaped frame matches the natural shape of the mitral annulus, allowing for accommodation of the left ventricular outflow tract (LVOT). The straight portion of the valve’s frame faces the LVOT allowing blood to flow, uninterrupted, into the aorta and ultimately into systemic circulation. The mitral valve must be securely anchored to withstand the pressure gradients that occur between the left atrium and ventricle throughout the cardiac cycle. The Tiara has three ventricular anchors, which are secured behind the anterior and posterior leaflets of the native valve, preventing retrograde displacement (into the left atrium) during systole. Paravalvular leak is prevented by the Tiara’s atrial skirt structure.

Implantation protocols

The implantation procedure is performed under general anesthesia and mechanical ventilation, and guided by transesophageal echocardiography (TEE), and fluoroscopy. A small incision is made inferior to the xyphoid process, exposing the apex of the heart and allowing for apical puncture. A purse string (U-shaped) suture is placed around the site of entry to maintain hemostasis following the removal of the delivery system. A J-tipped 0.035 inch guidewire is then advanced through the left ventricle and across the native mitral orifice. The catheter, loaded with the Tiara apparatus is then advanced over the guidewire, to be positioned in the left atrium. Central positioning of the Tiara delivery system in the native mitral orifice is confirmed using TEE and angiography before the guidewire is removed and the valve is deployed. The valve opens in a particular sequence. First the atrial skirt is deployed and the valve is positioned so the flat portion of the D-shaped frame is adjacent to the LVOT. Once the Tiara is aligned, the valve is pulled downward and seated on the annulus. The ventricular portion is then deployed and anchored. It is anchored behind the anterior and posterior leaflets of the native valve. Finally, the delivery system is removed and hemostasis is maintained by the purse string suture. Heart and valve function is monitored following the procedure.

References

Transapical transcatheter mitral valve implantation of the Tiara bio-prosthesis Wikipedia