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Heart valve replacement success may depend on age, valve type

[November 09, 2017] By Gene Emery

(Reuters Health) - People who need a heart valve replaced often face a dilemma: should they have a mechanical valve made of graphite or a biological valve derived from a cow or pig? A new study suggests the answer depends on the age of the patient and which of the heart’s valves needs to be replaced.

About 2.5 percent of the U.S. population may need valve replacement. Biologic valves are more prone to deterioration and may require a second operation. Mechanical valves last longer, but patients have to take a blood thinner for life to prevent dangerous clots and bleeding.

The American College of Cardiology and the American Heart Association currently recommend mechanical valves for people under age 50 and biologic valves for those over 70. Between those ages, the groups say, neither type has a clear advantage.

But the new study published in the New England Journal of Medicine, which used death rates for 25,445 replacement surgeries in California from 1996 through 2013, found that it makes a difference whether patients need a mitral valve, which leads to the main pumping chamber of the heart, or an aortic valve, which regulates blood coming out of the heart.

"With aortic valves, our findings pretty much mirrored what the guidelines suggest or might actually support an earlier age for putting in biological valves," senior study author Dr. Joseph Woo, a cardiothoracic surgeon at the Stanford University School of Medicine in California, told Reuters Health in a telephone interview. "For the mitral valve it was the exact opposite."

The issues are complicated, however, by the question of whether most mitral valves really need to be replaced as well as the lifestyle limitations brought on by mechanical valves, said Dr. Robert Bonow, a past president of the American Heart Association who helped write the current guidelines but was not involved in the new study.

For example, when it came to mitral valves, Woo and his colleagues found that a pig or cow valve more than doubled the risk of death within 30 days for patients aged 40 to 49. The death rate was 5.6 percent with a biologic valve versus 2.2 percent with a mechanical one. Yet with older patients, the type of device didn't seem to make a difference in mortality risk.

Over the longer term, younger recipients of a biologic valve also fared worse. In the 40 to 49 age group, the death rate at 15 years was 44.1 percent with a biologic valve and 27.1 percent with a mechanical valve. In the 50- to 69-year-old patients, the added risk associated with a biologic valve was not as high while in older patients there was no difference.

The odds of stroke were also higher among people who had mechanical mitral valve replacements, but only in the 50 to 69 age group. The risk of bleeding was lower among mitral valve patients with a biologic valve if they were aged 50 to 79.

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Yet in reality, most mitral valves should be repaired, not replaced, said Bonow, who directs the Center for Cardiovascular Innovation at Northwestern University's Feinberg School of Medicine in Chicago.

"If you're going to get a mitral valve replacement, it's better with a mechanical valve," he told Reuters Health by phone. "But even better, let's get a surgeon who can repair it. Not every mitral valve can be repaired, but the majority can."

Surgeons often prefer replacement because it requires less expertise than re-tailoring an existing valve to keep it from leaking.

When it came to aortic valve replacement, the type of valve used did not affect overall mortality. But age at the time of replacement did.

“It’s only marginally better to get a mechanical valve" if you're 45 to 54, Bonow said, but dealing with the fallout of getting a mechanical valve poses "huge lifestyle issues," because recipients have to be on a blood thinner for the rest of their lives.

"A lot of times, once you describe the lifestyle issues, people will usually opt for the biological valve."

That may explain why the Woo team found that biologic valves became increasingly popular during the study period, representing 51.6 percent of the cases of aortic-valve replacements in recent years versus 11.5 percent in 1996. Similarly, with mitral valves, the share of biologic prostheses went from 16.8 percent in 1996 to 53.7 percent in 2013.

Woo acknowledged that the new findings don't make decision-making easier for patients and their doctors. The results add nuances to the recommendations, he said.

SOURCE: http://bit.ly/2h5QjyQ New England Journal of Medicine, online November 8, 2017.

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