Preclinical Data Show Safety, Efficacy of Transcatheter Mitral Valve

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A novel self-expanding, transcatheter mitral valve bioprosthesis shows promise as an alternative to open mitral valve repair or replacement for patients at unacceptable risk for surgery, according to a preclinical study published in the February 2014 issue of JACC: Cardiovascular Interventions.

The Tiara mitral valve device (Neovasc, Vancouver, Canada) is a self-expanding bioprosthesis with cross-linked bovine pericardial tissue leaflets mounted inside a metal alloy frame. It is designed to be implanted using the transapical approach.

Researchers led by Shmuel Banai, MD, of the Tel Aviv Medical Center (Tel Aviv, Israel), conducted a 3-part preclinical study:

  • Acute animal model: Healthy swine (n = 36) were implanted and followed for at least 90 minutes before being euthanized
  • Chronic animal model: Sheep (n = 7) were implanted and followed for an average of 150 days
  • Human cadaver model: The device was implanted in freshly defrosted human hearts (n = 24) from both patients with normal cardiac anatomy and those with a history of severe mitral regurgitation, LV dilatation, and aortic valve regurgitation

Placement, Positioning Optimal

Valves were successfully implanted in 81% of the swine (n = 29). Unsuccessful implantation was due to improper positioning (n = 3), failure of the valve anchors to properly engage during deployment (n = 2), and ventricular fibrillation (n = 2). None of the valves migrated or embolized during or after implantation. The authors report that there was a steady increase in the rate of successful implantation as the series progressed.

Of the animals with successful implantation, all remained hemodynamically stable throughout the procedure. Some A-fib was noted when the valve was being manipulated, but there were no sustained or hemodynamically relevant arrhythmias after implantation. Substantial paravalvular leak was seen only in animals with a mismatch between the mitral valve annulus size and the prosthesis diameters.

All of the implanted sheep remained clinically stable throughout follow-up. Echocardiographic assessment showed proper positioning and alignment. There was evidence of mild valvular mitral regurgitation (n = 2) and mild or moderate paravalvular leak (n = 6), but these complications did not have hemodynamic significance.

Of the human hearts, half had moderate and severe mitral regurgitation and 29.2% had congestive heart failure. Implantation resulted in “appropriate geometrical positioning with full circumferential coverage of the atrial aspect of the mitral annulus . . . and good apposition and location of the ventricular anchoring system,” Dr. Banai and colleagues write.

More Valve Sizes Needed

The authors attribute a relatively high rate of paravalvular leak to the fact that only 1 size of the valve was available for implantation, making “size mismatch between the native annulus and prosthetic device” unavoidable in many hearts.

Transcatheter mitral valve implantation “has the potential to become the preferred intervention to treat severe mitral regurgitation in patients who are at high risk for surgery, since it can theoretically reduce mitral regurgitation to an extent similar to that of surgery while preserving the mitral apparatus,” they continue.

Still, the authors acknowledge several challenges. First, “the ideal device must be stable and resistant to displacement or migration while enduring continuous cyclical movements of the mitral annulus and the base of the heart, as well as the high pressure gradients that are generated across the mitral valve,” they observe. Valve materials must also be “durable enough to withstand the loads generated.”

Looking forward, the authors say they hope that “the results of the ongoing preclinical experiments of the Tiara valve will . . . lead the way to human clinical trials.”

Study Details

The human hearts were harvested from patients 38-94 years, most of whom were female (70.8%).

 


Source:
Banai S, Verheye S, Cheung A, et al. Trans apical mitral implantation (TAMI) of the Tiara bio-prosthesis: Pre-clinical results. J Am Coll Cardiol Intv. 2014;7:154-62.

 

 

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Disclosures
  • Dr. Banai reports serving as the medical director of Neovasc.

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