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

Abstract

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 2017.1Schofer J Colombo A Klugmann S et al.Prospective multicenter evaluation of the direct flow medical transcatheter aortic valve.J Am Coll Cardiol. 2014; 63 (doi:10.1016/j.jacc.2013.10.013.): 763-768Google Scholar 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.2Dvir D Webb J Brecker S et al.Transcatheter aortic valve replacement for degenerative bioprosthetic surgical valves: results from the global valve-in-valve registry.Circulation. 2012; 126: 2335-2344Google Scholar 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.3Allen KB Chhatriwalla AK Saxon JT et al.Bioprosthetic valve fracture investigators. Bioprosthetic valve fracture: technical insights from a multicenter study.J Thorac Cardiovasc Surg. 2019; 5 (doi:10.1016/j.jtcvs.2019.01.073.): 1317-1328Google Scholar 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. In the first case with the use of a 24 mm TRUE balloon, at 8 ATM the fabric ripped at a small spot, at 13 ATM the ventricular ring cracked, and at 18 ATM the TRUE balloon burst. After dissection of the ventricular ring a cracked mark was found in the aortic ring at one position, but the ring stayed intact and did not break completely. Another three 25 mm valves were dilated with 24 mm balloons. With increasing inflation pressure 2 valves had a fabric tear and frame crack at 10 ATM; the third valve did not have any tear or fracture going up to 12 ATM. With the use of a 26 mm TRUE balloon at 4 ATM the fabric ripped and one post and the ventricular ring broke. At 12 ATM also the aortic ring cracked but stayed in shape as the fabric still held everything together. However, after the fabric was removed, approximately one-third of the aortic ring came off from the cuff. Based on these findings, BVF of the DFM THV can lead to disruption of the fabric and to splitting of the polymer, and therefore the operators must exercise caution. At our institution 170 DFM valves were implanted between October 2014 and November 2016. After a mean interval of 4.3 years, 7 patients required a VIV procedure because of valve failure due to re-stenosis (mean gradient 39.7 mm Hg, range 30–72 mm Hg). After VIV implantation the mean gradient was 11.1 mm Hg (range 5–15 mm Hg). In 4 patients pre- and/or postdilation with undersized balloons was performed with low inflation pressure to avoid ring fracture. Because the implantation of a balloon-expandable valve in the first patient resulted in a mean transvalvular gradient of 15 mm Hg, the following patients received self-expanding valves (leading to a mean transvalvular gradient of 10.5 mm Hg, range 5–14 mm Hg). Based on this limited experience in the treatment of degenerated DFM valves, we would recommend use of self-expanding valves and—if pre-/postdilatation is necessary—the use of undersized balloons with low pressure inflation.