For patients who need complex surgery, the best surgeon may be one who specializes in one procedure—not just an active surgeon who performs several operations.

Specialists reduced mortality rates for certain procedures by as much as half, new research shows. The new study builds on the longstanding view that the busiest doctors get the best results. Copious research shows patients of active surgeons are less likely to die or suffer complications from an operation.

The study, published in July in the BMJ, analyzed more than 695,000 operations performed by 25,000 surgeons in the U.S. between 2008 and 2013. Researchers looked at patients who had one of eight complex cancer and heart surgeries. Entering the study, mortality rates for the eight procedures ranged from 1 percent to 7 percent.

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For six of those procedures, patients were less likely to die in the first month after surgery when the operation they underwent accounted for a larger share of surgeons’ overall practices. Researchers looked for doctors who specialized in a specific procedure, such as heart valve replacement, rather than whether surgeons specialized in cardiology.

The results suggest a surgeon who performs 20 valve replacements and nothing else may get better results than a doctor who performs 40 valve replacements and 60 other surgeries, the authors said.

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