June 25 (HealthDay News) -- A new Canadian study adds compelling support for current recommendations that people who first get clot-dissolving treatment for heart attacks should have artery-opening angioplasty as soon as possible afterward.

"This study strengthens the guideline recommendations," said Dr. Warren J. Cantor, an assistant professor of medicine at the University of Toronto and lead author of a report in the June 25 issue of the New England Journal of Medicine. "The original recommendation was based on a limited number of trials. This is the largest trial done to date looking at the strategy of doing angioplasty routinely after fibrinolysis [clot-dissolving therapy]. It confirms that it is a safe approach with no increase in major bleeding, and that patients do better when they undergo angioplasty."

Immediate angioplasty after a heart attack is best, but many medical centers are not equipped to do the procedure on an emergency basis, Cantor noted. "In most centers in the world, patients receive clot-busting medication," he said. "Many are routinely transferred to a center where they can undergo angioplasty."

The study shows that angioplasty should be done within six hours, Cantor said.

The study included 1,059 people who had major heart attacks and were given clot-dissolving treatment at Canadian medical centers not equipped for angioplasty. Half were assigned to standard treatment, clot-preventing drugs with aspirin and the blood thinner heparin, with angioplasty done when possible. The other half were transferred to centers where angioplasty could be done within six hours.

Nearly 90 percent of those getting standard treatment did have angioplasty, done after an average wait of more than 32 hours. Nearly all those transferred for quick angioplasty had it in less than three hours. After six months, 11 percent of those who had quick angioplasty had a major adverse cardiac event or died, compared to 17.2 percent of those assigned to standard treatment.

Guidelines of the American Heart Association and American College of Cardiology recommend the quick angioplasty strategy, but "the evidence for it was fairly limited until recently," Cantor said. "Older studies said there might be more harm than good, with major bleeding."

"That was true back then, but we are talking about a generation ago," said Dr. Jeffrey W. Moses, director of the Center for Interventional Vascular Therapy at New York-Presbyterian Hospital/Columbia University Medical Center. "With stents and drugs like Plavix, the world has changed."

Stents are flexible metal tubes inserted to keep arteries open following angioplasty, and Plavix is a potent clot-dissolving drug.

Several studies have compared clot-dissolving therapy with angioplasty in the hours after a heart attack, "and angioplasty is better," Moses said. While statistics are vague, probably only half the people who suffer heart attacks in the United States get angioplasty as the first treatment, he said.

"If you get clot-busters, you should have angioplasty as soon as possible, at that site or somewhere else," Moses said.

The case for limiting heart attack treatment to clot-dissolving therapy has been lost, Cantor said.

"Recent studies using contemporary equipment suggested a much safer and effective treatment, and we confirm it in the largest trial yet done," he said.

SOURCES: Warren J. Cantor, M.D., assistant professor, medicine, University of Toronto; Jeffrey W. Moses, M.D., director, Center for Interventional Vascular Therapy, New York-Presbyterian Hospital/Columbia University Medical Center, New York City; June 25, 2009, New England Journal of Medicine