Heart failure patients with clogged arteries have a better chance of surviving 10 years if they get bypass surgery plus medicine rather than just drugs alone, according to an international study.

Earlier results from the same research raised questions about the benefits of bypass versus medicine alone, but researchers say the long-term evidence clearly favors the surgery.

The lead author of the study, Duke University cardiologist Dr. Eric Velazquez, said the results "are so definitive and so robust" that they would likely to lead to stronger recommendations favoring bypass surgery for these patients.

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Nearly 6 million Americans and 23 million people worldwide have heart failure, and many of them also have artery disease similar to those studied. In recent years, bypass surgery has increasingly been recommended for such patients, along with medicines to ease heart failure symptoms.

Concerns were raised when results after nearly five years of research showed about equal number of deaths in bypass patients and in those who got only medicine, despite fewer heart-related deaths in the bypass group. Those findings were published in 2011.

The 10-year results were published online Sunday in the New England Journal of Medicine and presented at an American College of Cardiology meeting in Chicago.

The study involved 1,200 heart failure patients in 22 countries, including the United States. Most were men around age 60 when the study began. All were taking heart medicines, and about half were assigned to also get bypass surgery.

More than half the patients in each group lived beyond the study's first phase. The 10-year results are a look back at all patients studied.

A total of 359 bypass patients died from any cause, or about 59 percent, compared with 398 medicine-only patients who died, or 66 percent.

Deaths from heart disease-related causes totaled 247 in the bypass group, or 41 percent, versus 297 medicine-only patients, or 49 percent.

A journal editorial published with the study says the latest results "solidly support" strengthening treatment guidelines to say that bypass surgery is "probably beneficial" for these patients.

The long-term results "are very encouraging" and confirm what many doctors believed about potential benefits of bypass for these patients, said Dr. Ted Feldman, a cardiologist at NorthShore University HealthSystem in Evanston, Illinois. Feldman was not involved in the study.

The National Heart, Lung and Blood Institute paid for the study.