Mechanical Valves Show Mortality Benefit Over Biologic Valves

Patrice Wendling

November 12, 2017

STANFORD, CA — New research suggests surgically implanted mechanical valves may offer better long-term survival than biologic prostheses, but much depends on the valve being replaced[1].

Receipt of a mechanical valve was associated with significantly lower 15-year mortality up to age 70 in patients requiring mitral-valve replacement, whereas this benefit was present only up to age 55 for those undergoing aortic-valve replacement.

"We were very surprised to find the benefit of mechanical valves really outlasted or exceeded that of biologic valves all the way up to age 70, when the neutral zone is 50 to 70," senior author Dr Y Joseph Woo (Stanford University, Stanford, CA) told | Medscape Cardiology.

"This is probably very different from what's going on in practice right now, where we're moving to biologic valves earlier and earlier.

Over the past 15 or 20 years, there has been a dramatic shift around the world in the increased use of bioprosthetic valves, Dr Michael Argenziano (Columbia University, New York City), who was not involved in the study, noted in a news release[2] from Stanford.

"This is the first paper to provide solid evidence that maybe we have been moving too quickly away from the mechanical valve," he said.

Woo observed that current practice guidelines are supported by anecdotal information and smaller underpowered trials and have been simplified over the years to recommend a mechanical valve for patients under age 50, a biologic valve for those over age 70, and "dealer's choice" of either a mechanical or biological valve for those 50 to 70 years, with no distinction made between valve positions.

Based on the current results, however, "reinstatement of valve-specific guidelines for the selection of a prosthesis warrants further exploration," the investigators write in the study, published November 9, 2017 in the New England Journal of Medicine.

Commenting for | Medscape Cardiology, Dr Ravi Dave (University of California Los Angeles) said, "What this study shows is that the difference is not just minor; there is a mortality benefit in the aortic and mitral position with mechanical valves.

"It brings up the question of whether we should be changing our practice and implement more metallic-valve use, and I think that's a question that needs to be answered on a case-by-case basis."

Bigger Data

To compare the long-term benefits and risks of the two prostheses in a large population, the investigators examined data from 25,445 patients from 142 California hospitals who underwent aortic- and mitral-valve replacement from 1996 through 2013. Patients receiving biologic valves were older and had more comorbidities.

Inverse probability weighting was performed to balance baseline characteristics.

Over the study period, the use of biologic valves increased significantly for aortic-valve (11.5% to 51.6%) and mitral-valve replacement (16.8% to 53.7%; both P<0.001).

At 15 years, mortality was significantly higher with a biologic aortic valve than a mechanical aortic valve among patients aged 45 to 54 (hazard ratio [HR] 1.23, P=0.03), but not those aged 55 to 64 at the time of surgery (HR 1.04, P=0.60). The results remained consistent after multivariable adjustment and inclusion of hospital as a random effect.

For mitral-valve replacement, mortality was higher with a biologic mitral valve for patients aged 40 to 49 years (HR 1.88, P<0.001) as well as those aged 50 to 69 years (HR 1.16, P=0.01), but not aged 70 to 79 years (HR 1.00, P=0.97).

"I'd say it's relatively uncommon for someone to recommend to, say, a 65-year-old or older patient a mechanical valve in the mitral position in practice, but in terms of outcomes, at least our paper would suggest your patient is going to be better off if you put in a mechanical valve."

The mortality benefit with the mechanical valve, however, came at the cost of a higher risk of bleeding and, in some age groups, stroke, but was associated with a significantly lower risk of reoperation than a biologic valve.

Notably, 30-day mortality rates after reoperation with a biologic prosthesis were 7.1% for aortic-valve reimplantation and 14% for mitral-valve reimplantation, "which is much higher than typically quoted or reported," Woo said.

"What we found is that the mitral and aortic positions behave very, very differently. And maybe we shouldn't be lumping these patients together but should be customizing the decision," he said.

When advising patients in the gray zone of age 50 to 70 in his own practice, Woo said, "For aortics I would probably lean toward biologics and for mitrals I would probably lean toward mechanicals."

"This study will definitely change the information that I give my patients," Dr Jennifer Lawton (Johns Hopkins University, Baltimore, MD), who was not involved with the study, said in the news release. "The benefit of this study is that it looks at so many patients over a period of time. Until now, there have only been small studies on which the guidelines are based."

That said, Dave observed this is an "ever-changing and dynamic field" that has witnessed a shift toward transcatheter-valve repair and replacement, and as such, the study is "probably outdated."

Also, the bioprosthetic valves used in the beginning of the study are no longer being used. "That technology is constantly improving, and the longevity of bioprosthetic valves is much better than what they started out with," he said.

As for what he'll tell his own patients, Dave said "In the mitral position, because a lot of these patients have other reasons why they need to be on anticoagulants and the metallic valve functions so well, in this position considering the metallic valve is a wise choice.

"In the aortic valve, you have to put a lot of other things into play; the age of the patient, the comorbidities, the willingness of the patient to be on lifelong anticoagulation."

The study was supported by the National Institutes of Health, the Agency for Healthcare Research and Quality, and Stanford University. Woo reports grants from National Institutes of Health outside the submitted work. Disclosures for the coauthors are listed on the journal website.

Follow Patrice Wendling on Twitter: @pwendl. For more from | Medscape Cardiology, follow us on Twitter and Facebook.


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