Mechanical heart valves may be safer in certain cases than those made of animal tissue and should be used more as a replacement, especially in younger patients, according to a study.
Researchers at the Stanford University School of Medicine in the US found that the best choice can hinge on whether the aortic or mitral valve is being replaced.
The study shows that for patients undergoing mitral valve replacement, a mechanical valve is actually beneficial until the age of 70.
On the other hand, for patients undergoing aortic valve replacement, the benefit of implanting mechanical valves ceased after the age of 55.
"This has potential to significantly impact the current national practice guidelines," said Joseph Woo, professor at Stanford.
Most patients who need open-heart surgery to remove a diseased heart valve face complicated conversations with their heart surgeons about whether to use a natural-tissue or mechanical valve as a replacement.
Mechanical valves can last a lifetime, but they come with increased risks of blood clotting and bleeding and a lifetime of having to take the blood-thinning medication warfarin.
Biological valves, which are most often made from pig or cow tissue, do not increase the risk of bleeding or clotting, but they wear out within about 10 to 15 years, making a second surgery likely.
The decision has been made difficult by the lack of sufficient scientific evidence to back up either choice, said Woo, senior author of the study published in The New England Journal of Medicine.
For those younger than 50, a mechanical valve is currently recommended, and for those older than 70, a biologic tissue valve is recommended, Woo said.
However, the guidelines do not distinguish between whether the mitral or aortic valve is being replaced.
"If you think about this just in terms of age, the older you are, the less likely that you will outlive the durability of a biological valve," Woo said.
Surgeons have noted in recent years a trend towards younger patients choosing biological valves, primarily because they do not want to deal with a lifetime of taking blood thinners and with the accompanying dietary restrictions and routine blood testing necessitated by a mechanical valve.
Researchers examined rates of mortality, stroke, bleeding and reoperation in patients who underwent heart-valve surgery at 142 hospitals in California between 1996 and 2013.
They examined the records of 9,942 patients who underwent aortic-valve replacement and 15,503 patients who underwent mitral-valve replacement during the study period.
Results showed a stark difference in health benefits depending on which valve was being replaced, Woo said.
The long-term mortality benefit associated with a mechanical valve compared with a biological valve persisted until age 70 in patients undergoing mitral-valve replacement, the study found.
For those undergoing aortic-valve replacement, this benefit persisted only until age 55.
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