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Woman taking aspirin.Thinkstock

The common practice of prescribing Aspirin to patients before surgery to prevent heart attacks is ineffective and likely does more harm than good, new Canadian research shows.

"You're not preventing heart attacks and mortality, but you are increasing the risk of significant bleeding," P.J. Devereaux, the head of cardiology at Juravinksi Hospital in Hamilton and principal investigator for the study, said in an interview.

About 50 per cent of non-cardiac surgery patients (for example, those undergoing hip replacement or bowel surgery) take Aspirin before their operations. Some are prescribed the drug specifically, while others are taking it routinely to reduce their cardiovascular risk.

Surgeons have long debated whether their patients should continue Aspirin use. The new data suggest that "holding it is much more rational," Dr. Devereaux said.

He said chronic users should stop taking Aspirin about three days before surgery, and resume doing so eight to 10 days after.

"Aspirin is beneficial in the non-surgical world, but, in the surgical window, there is a risk of significant bleeding," he said.

Dr. Devereaux also stressed that these findings do not relate to prescribing a blood thinner like heparin after surgery to prevent blood clots, and that practice should continue.

The research, published in the New England Journal of Medicine, was presented on Monday morning at the American College of Cardiology conference in Washington.

The study involved 10,010 patients in 135 institutions in 23 countries who were awaiting non-cardiac surgery. Half received Aspirin, and half did not.

Researchers found that 7 per cent of those in the Aspirin group had a heart attack or died within 30 days of surgery, compared to 7.1 per cent of those who received a placebo, meaning there was no benefit.

Additionally, 4.6 per cent of patients in the Aspirin group had significant bleeding, compared to just 3.8 per cent among the placebo group.

There was no difference in the outcomes for chronic Aspirin users and those who took it specifically before surgery.

A second related study, also published in the New England Journal of Medicine, found that the drug clonidine – which is prescribed to about 20 per cent of patients with atherosclerosis (hardening of the arteries) – to prevent heart attacks, is also ineffective and potentially harmful.

The research showed that 6.6 per cent of patients getting clonidine before surgery had a heart attack or died within 30 days, compared to 5.9 per cent who got placebos.

In addition, 48 per cent of surgery patients who took the drug suffered hypotension (very low blood pressure), compared to 37 per cent in the placebo group. Very low blood pressure can damage the heart and brain.

"There is no good reason to give perioperative clonidine to prevent heart attacks or death," Dr. Devereaux said.

About 200 million people a year undergo major non-cardiac surgery a year, and 10 million of them have a major heart-related complication, so researchers have long sought ways to reduce that risk.

Dr. Devereaux said finding that cheap drugs like Aspirin and clonidine do not help is a disappointment, but the silver lining is that discontinuing these practices will reduce harm.

"Any day our research helps patients is a good day," he said.

Follow me on Twitter: @picardonhealth