Although mitral valve repair remains the procedure of choice for mitral valve disease when anatomy allows, valve replacement continues to be common, with approximately 6000 mitral valve replacements performed annually in the United States—30% of which involve mechanical prostheses. Because of the structural deterioration of bioprostheses, mechanical valves are associated with better long-term survival and lower reoperation rates in specific groups, particularly younger patients, for whom the bleeding risk associated with vitamin K antagonists is relatively lower.

On-X® prostheses (Artivion®) are bileaflet mechanical valves available in two mitral designs: Standard (sizes 23, 25, 27/29, 31/33 mm) and Conform-X (single size 25/33 mm). The PROACT Mitral trial was a prospective, randomized, open-label study comparing low-dose versus standard-dose warfarin therapy (target INR 2.0–2.5 vs. 2.5–3.5, respectively). The study did not demonstrate noninferiority of the low-dose regimen.

The present study analyzes secondary outcomes from the PROACT Mitral trial: survival, clinical status (NYHA functional class), and echocardiographic hemodynamic parameters of the two On-X® valve types. Patients were evaluated postoperatively at 3 months, 6 months, 1 year, and annually for up to 8 years. NYHA class was assessed at each visit, and echocardiography was performed at 1, 3, and 5 years to determine mean gradient (MG).

The mean patient age was 55 years. The most frequent etiologies were rheumatic and degenerative/myxomatous disease. Overall survival was 92.3% for all On-X® valves, 91.1% for the Standard valve, and 93.6% for the Conform-X (log-rank p = .53). The linearized reoperation rate was 0.66% per patient-year, with a 5-year cumulative incidence of 5.8%. Mean transvalvular gradient was 4.6 ± 2 mm Hg, showing a positive correlation with body surface area (BSA) and a statistically significant trend toward higher gradients in larger BSA categories for Standard valves sized 25 and 27/29 mm. This trend was not observed in Standard 31/33 mm or Conform-X valves. Over time, gradients remained stable across all prosthesis sizes and BSA groups, indicating durable hemodynamic performance.

Functional class assessment demonstrated consistent improvement: 96.6% of patients were in NYHA classes I–II at 3–5 years, and this improvement was maintained at 5 years. A higher incidence of NYHA class III was noted among patients with the 25 mm Standard valve.

COMMENTARY:

Mitral valve replacement remains a frequently performed operation, particularly in younger patients unsuitable for repair, who are the main candidates for mechanical prostheses. Studies like this are highly relevant, as they provide evidence of long-term outcomes beyond clinical improvement—namely survival and durability.

The On-X® valve system offers two cuff configurations: a thin sewing ring available in multiple sizes (Standard) and a wider “universal” cuff (Conform-X 25/33 mm) designed to accommodate annuli between 25 and 33 mm, with sutures placed around an enlarged outer sewing ring. A significant interaction between BSA and valve size was observed, though large models (Standard 31/33 mm and Conform-X 25/33 mm) were not affected by this trend. This finding should be considered during valve selection at implantation. Moreover, the stability of gradients from early to midterm follow-up (3–5 years) across all valve sizes suggests sustained hemodynamic performance and supports the valve’s durability.

Regarding functional outcomes, there was a consistent improvement in NYHA class, though the higher incidence of class III in patients with 25 mm Standard valves warrants further investigation. Overall, the data indicate that On-X® mechanical mitral valves are a reliable and durable option, providing favorable survival, stable hemodynamics, and improved functional capacity at mid- to long-term follow-up.

REFERENCE:

Ruel M, Chu MWA, Graeve A, Gerdisch MW, Damiano RJ Jr, Smith RL, et al. for the PROACT Mitral Investigators. Midterm survival, clinical, and hemodynamic outcomes of a novel mechanical mitral valve prosthesis. J Thorac Cardiovasc Surgery. 2025;170(4):1060-1068.e3. https://doi.org/ 10.1016/j.jtcvs.2024.11.029