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Bioprosthestic Valve Fracture of the Direct Flow Medical Valve — A Bench Test

The Direct Flow Medical (DFM) valve (Direct Flow Medical, Inc., Santa Rosa, CA) is a nonmetallic transcatheter heart valve (THV) that was approved in Europe in October 2014 for the treatment of aortic stenosis and retrieved from the market after failing to secure funding in January 2017. The valve consists of independently inflatable smaller lower (ventricular) and bigger upper (aortic) rings, which encircle and capture the native valve annulus. After insertion into the left ventricular cavity, the ventricular ring is pressurized with saline and contrast solution and positioned at the native annulus using 3 independent positioning wires. Then the aortic ring is pressurized and valve hemodynamics are evaluated. When an optimal final position is achieved, the contrast–saline mixture gets replaced by a solidifying polymer that provides a permanent support structure to fixate the valve in position. The DFM THV was implanted in many patients. In the near future an increasing number of patients is expected to present with bioprosthesis degeneration. In contrast to balloon-expandable or self-expanding THVs, the DFM valve has a ventricular ring, located in the left ventricular outflow tract, which determines—similar to a surgical bioprosthesis —the size of the THV selected for a valve-in-valve (VIV) procedure. Previous studies have demonstrated that VIV transcatheter aortic valve replacement (TAVR) in patients with small surgical bioprostheses or with preexisting prosthesis–patient mismatch (PPM) can result in high residual transvalvular gradients and reduced 1-year survival. Surgical bioprosthetic valve fracture (BVF) has recently been introduced and proved to be feasible for decreasing the transvalvular gradient after a VIV procedure in small degenerated aortic bioprostheses, thereby reducing prothesis– patient mismatch. For this purpose, a noncompliant balloon is used that is oversize in relation to the true internal diameter (ID) of the bioprosthesis by approximately 4 mm. To study whether BVF can also be applied on the DFM THV, bench tests were performed (Figure 1). Five 25 mm DFM valves with solidified polymer, which have a true ID of 20 mm, were dilated either with a 24 mm (n = 4) or a 26 mm TRUE dilatation balloon valvuloplasty catheter (Bard Peripheral Vascular, Inc., Tempe, AZ) at different pressure levels (ATM), and thereafter the fabric and the polymer were analyzed.