Transapical mitral implantation of the Tiara bioprosthesis: pre-clinical results

Abstract

Objectives: This study sought to describe the pre-clinical evaluation of transapical mitral implantation of the Tiara (Neovasc Inc, Vancouver, British Columbia, Canada) valve in preparation for first-in-man implantation.

Background: The Tiara is a transcatheter self-expanding mitral bioprosthesis, specifically designed for the complex anatomic configuration of the mitral apparatus.

Methods: Tiara valves were implanted in a short-term porcine model, in a long-term ovine model, and in human cadavers.

Results: Short-term and long-term evaluation demonstrated excellent function and alignment of the valves, with no left ventricular outflow tract obstruction, coronary artery obstruction, or transvalvular gradients. Long-term evaluation of 7 sheep demonstrated clinically stable animals. A mild degree of prosthetic valve regurgitation was seen in 2 of the 7 sheep. A mild-to-moderate degree of paravalvular leak, which was attributed to this animal model, was observed in 6 of these animals. Cardioscopy and macroscopic evaluation demonstrated stable and secure positioning of the Tiara valve with no evidence of injury to the ventricular or atrial walls. Pericardial leaflets were free and mobile without calcifications. Implantation of the Tiara valves in human cadaver hearts demonstrated, upon visual inspection, proper anatomic alignment and seating of the valve, both at the atrial and at the ventricular aspects of the native mitral apparatus.

Conclusions: In preparation for the first-in-man transcatheter mitral valve implantation, we report the successful pre-clinical evaluation of the Tiara transcatheter self-expanding mitral bioprosthetic valve. In porcine and ovine models without mitral regurgitation, transapical mitral implantation of the Tiara valve is technically feasible and safe, and results in a stable and well-functioning mitral bioprosthesis.

Keywords: mitral regurgitation; mitral valve; mitral valve implantation; transapical; transcatheter.

Figure 1. Tiara and delivery system

Front and profile views of the Tiara (upper panel). The “D” shape of the valve, the atrial “skirt” which engages the atrial aspect of the mitral anulus, and the saddle shaped valve are clearly seen Trans-apical delivery system (lower panel)

Figure 2. Implantation sequence of the Tiara

A: The CS wire outline the MV anulus. The pigtail catheter is antriorly, in the ascending aorta, delivery system is through the mitral anulus into the left atrium B: Atrial skirt is starting to open in left atrium, the flat aspect of the ‘D” shaped Tiara are facing anteriorly C: Atrial skirt is open and positioned on the atrial aspect of the mitral anulus, and the ventricular portion of the Tiara is delivered into position just before valve final release D: Final release of the Tiara, before removal of the delivery system

Figure 3. 3D echocardiogram of the implanted Tiara™ 150-days post implantation

The “D” shaped Tiara™ is clearly seen. Left - the Tiara™ is closed during systole and the three leaflets are seen. Right - Tiara™ is open during diastole and the native aortic valve is closed

Figure 4. Coronary angiography and left ventriculograpy 150 days post Tiara™ implantation

Left: Patent coronary arteries, without evidence of impingement or obstruction of the left circumflex coronary artery are shown Right: Left ventriculography in a sheep 150 days following TAMI

Figure 5. Ventricular view of the Tiara™ 150 days after implantation in sheep's heart

The papillary muscles (held by clamps), chordae tendineae and the sub-valvular mitral apparatus are intact. Valve frames are covered with fibrous tissue growth adequate for healing. Pericardial leaflets are intact without tears or perforations, there was no evidence of endocarditis or leaflet calcification, and the myocardium adjacent to the device is intact

Figure 6. Atrial view of the Tiara™ 150 days after implantation in sheep's heart

Picture was taken after the roof of the atrial wall was removed. The atrial “skirt” of the Tiara™ is well seated on the atrial aspect of the mitral annulus. Valve frames are covered with fibrous tissue growth adequate for healing. Pericardial leaflets are intact without tears or perforations; there was no evidence of endocarditis or leaflet calcification. The adjacent atrial wall is intact and free of inflammation or necrosis.

Figure 7. Atrial view of the Tiara™ implanted in a human cadaver heart with history of severe mitral regurgitation

The atrial “skirt” of the Tiara ™ is well seated on the atrial aspect of the mitral annulus. The Tiara is aligned so that the flat aspect of the “D” shaped Tiara ™ is properly facing the aorticmitral curtain.