ÌÇÐÄvlog

In patients undergoing aortic or mitral valve surgery, the choice between a mechanical or bioprosthetic valve replacement remains controversial. Specifically, different guidelines suggest different age thresholds for preferring a bioprosthetic over mechanical valve. Even more importantly, clinical practice often diverges from current guideline recommendations.

This controversy is addressed in the study by Park et al¹ based on data from the Korean National Health Insurance Service administrative claims database that included 24 374 adults who underwent aortic valve replacement (AVR) or mitral valve replacement (MVR) between 2003 and 2018. Over a 15-year follow-up, in patients undergoing AVR, the unadjusted primary end point of all-cause mortality was 17% with a mechanical valve and 28% with a bioprosthetic valve. Similarly, unadjusted all-cause mortality in those undergoing MVR was 17% with a mechanical valve and 36% with a bioprosthetic valve, with a relatively even split between cardiovascular and noncardiovascular mortality. As expected, there was a higher risk of reoperation for valve dysfunction with bioprosthetic valves, regardless of age or valve position. Conversely, the risk of bleeding and thromboembolic events was higher in patients age 55 years or older undergoing AVR.

Importantly, the primary end point of all-cause mortality was significantly associated with patient age at the time of implantation. Comparing a bioprosthetic and mechanical AVR, the adjusted hazard of all-cause mortality was higher for patients younger than 55 years (adjusted hazard ratio [aHR], 2.18; 95% CI, 1.32-3.63) and patients aged 55 to 64 years (aHR, 1.29; 95% CI, 1.02-1.63) but lower for patients aged 65 years or older (aHR, 0.77; 95% CI, 0.66-0.90). In patients undergoing MVR, all-cause mortality was lower with a mechanical valve up to age 70 years, with no difference between mechanical and bioprosthetic AVR in patients aged 70 years or older. In addition to analysis by age groups, spline analysis was used to evaluate age as a continuous variable. This approach identified an age of approximately 65 years for AVR and 70 years for MVR as the point when a bioprosthetic valve was associated with a greater survival benefit than a mechanical valve.

These findings add support to the American College of Cardiology and American Heart Association (ACC/AHA)² and European Society of Cardiology and European Association for Cardio-Thoracic Surgery (ESC/EACTS) guidelines³ which both recommend a bioprosthetic AVR for patients older than 65 years. In contrast to the ESC/EACTS guidelines, which recommend a mechanical AVR for patients younger than 60 years, the ACC/AHA guidelines suggest that either a bioprosthetic or mechanical AVR is reasonable for patients aged 50 to 65 years, depending on patient comorbid conditions, risk of repeat valve surgery, patient preferences, and shared decision-making. Although a mechanical AVR is recommended in patients younger than 50 years in the ACC/AHA guidelines, many of these patients now can avoid a prosthetic valve with improved surgical approaches to aortic valve repair, use of a pulmonic autograph in the aortic position (often referred to as the Ross procedure), or, in patients with dilation of the aortic sinuses, graft replacement of the aortic root with aortic valve reimplantation (the David procedure).

In patients undergoing MVR, both the ACC/AHA and ESC/EACTS guidelines recommend a mechanical valve in patients younger than 65 years, rather than younger than 70 years, as suggested by this new study by Park et al,¹ although the ESC/EACTS guidelines do suggest a bioprosthetic MVR only for patients older than 70 years. Both guidelines emphasize the importance of avoiding a prosthetic mitral valve whenever possible, recommending surgical valve repair in patients with mitral valve prolapse or balloon valvuloplasty in patients with rheumatic mitral stenosis.

Underlying all these recommendations, the core challenge in choosing between a mechanical or bioprosthetic valve is the balance between the likelihood of bioprosthetic valve degeneration and the risks of long-term vitamin K antagonist anticoagulation with a mechanical valve. Bioprosthetic valves have the advantage of not requiring anticoagulation but are prone to fibrocalcific degeneration, leading to stenosis or regurgitation, as well as a higher risk of endocarditis than with a mechanical valve.⁴ Paradoxically, observational studies show that bioprosthetic valve durability is inversely associated with age, so not only do younger patents live longer, but significant valve dysfunction occurs fewer years after implantation than in older patients. In contrast, mechanical valves are very durable but require lifelong anticoagulation, with the attendant risks of thromboembolic and bleeding events.

As the data from Park et al¹ confirm, all-cause survival was higher with a mechanical valve in younger patients and with a bioprosthetic valve in older patients, lending support and allowing refinement of current guideline recommendations for the age threshold for optimizing valve choice. But defining a specific age threshold is not enough; valve choice depends on several other considerations. Vitamin K antagonist therapy limits diet and lifestyle, is inconvenient and requires frequent monitoring, with meticulous attention to maintaining therapeutic anticoagulation. Patients have differing attitudes to undergoing repeat surgery, concurrent medical issues affect risk of adverse outcomes with either valve choice, and needed valve durability depends on the patient’s expected longevity. Even in otherwise healthy patients, life expectancy varies considerably among countries. Overall, the difference in life expectancy at birth between Korea and the US is approximately 5 to 6 years, although this survival difference narrows at older ages. For example, the expected remaining years of life at age 65 years is 23.6 years for a Korean woman (19.2 years for a Korean man) compared with 19.8 years for a US woman (17.0 years for a US man).⁵ These differences in life expectancy translate into similar differences in the age thresholds for preferring bioprosthetic over mechanical valves.

In patients considering AVR, the options of a transcatheter intervention rather than a surgical procedure also impacts clinical decision-making. Even if there might be a higher risk of permanent pacer implantation with the transcatheter approach, patients often consider that avoidance of a chest wall scar and cardiopulmonary bypass, with a shorter hospitalization, less pain, and more rapid return to normal activities, outweighs any disadvantages of a bioprosthetic valve.⁶

Looking forward, it is likely that the optimal age thresholds for a specific valve type will shift with advances in valve disease therapies. Ideally, medical therapies will be developed to prevent, slow, or reverse valve disease progression. When intervention is needed, it is hoped that improved surgical techniques will allow repair of the native valve in more patients. Perhaps improved design and anticalcification treatment, or even tissue-engineered valves with the patient’s own cells, will provide improved bioprosthetic valve durability across the age spectrum. Possibly, mechanical valves will be developed using nonthrombogenic materials. Furthermore, if anticoagulant therapy still is needed, optimistically, a medication that is safe, effective, and easy to use will become available.

Importantly, there is an apparent divergence between guideline recommendations and clinical practice. In the cohort included in the study by Park et al¹ the use of bioprosthetic, rather than mechanical, AVRs increased from 9.8% early in the study to 43.2% by the end of the study. Similarly, the percentage of bioprosthetic mitral valves increased from 16.3% to 35.3%. Although it is likely that patient-centered consideration account for at least some these trends, Park et al¹ emphasize that shared decision-making requires clear communication by health care practitioners about the survival benefit associated with a mechanical prosthetic valve in younger patients. Given this information, many patients may choose a longer life over short-term considerations. Clearly, we need additional research on optimal approaches to communicating competing risks to patients and engaging patients in informed, shared decision-making.⁷

Published: May 22, 2023. doi:10.1001/jamanetworkopen.2023.14628

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2023 Otto CM. ÌÇÐÄvlog Open.

Corresponding Author: Catherine M. Otto, MD, Division of Cardiology, Box 356422, University of Washington, Seattle, WA 98195 (cmotto@uw.edu).

Conflict of Interest Disclosures: None reported.