Surgery of any kind -- not just heart surgery -- may raise a person's risk for having a heart attack, research has shown. Doctors often start patients on a low dose of aspirin shortly before and after their procedures to help prevent those events.
But the new study, which pitted aspirin against a dummy pill ("placebo") in over 10,000 patients who were having major surgeries that didn't involve their hearts, found that not only did aspirin fail to prevent heart attacks, it also significantly increased the risk of major bleeding.
The authors pointed out that many patients were already taking other drugs meant to prevent blood clots.
The most common surgeries in the study were orthopedic procedures like joint replacements.
The study was presented Monday at the annual meeting of the American College of Cardiology in Washington, D.C., and jointly published online in the New England Journal of Medicine.
The finding stunned several experts.
"This is something that has been hotly debated for years," said Dr. Kurt Pfeifer, an associate professor at the Medical College of Wisconsin, in Milwaukee. Pfeifer practices perioperative medicine, a specialty that focuses on getting patients safely through surgery.
"The paradigm had shifted a number of years ago to fairly routinely operating through aspirin with the idea that we were reducing the risk of cardiovascular events," said Pfeifer, who wasn't involved in the research. "That's what's troubling about this study," he added.
"This is unexpected," agreed Dr. Steve Cohn, medical director of the Uhealth Preoperative Assessment Center at the University of Miami Hospital. "We were thinking aspirin was potentially protective," said Cohn, who was not involved in the research.
For the study, researchers recruited patients from 135 hospitals in 23 countries. Half were randomly assigned to take 200 milligrams of aspirin just before surgery and then to continue on 100 milligrams for up to a month after surgery. The other half took a placebo pill.
Half of the patients were already taking a low-dose aspirin every day when they entered the study. Those patients were told to stop their daily aspirin at least three days before surgery and pick it up again seven days after.
The average age of patients who participated in the study was 68, almost evenly divided between women and men. About a third of patients in both groups had a history of blood clots that had caused heart attacks, strokes, or peripheral vascular disease. And nearly two-thirds also got some kind of additional blood thinner, typically Lovenox or Xarelto, to prevent clots.
Nearly the same number of patients, about 7 percent, died or had a heart attack within 30 days of their surgeries, whether they took aspirin or the placebo -- 351 of 4,998 patients in the aspirin group compared with 355 of 5,012 patients who took the placebo. That was true even for patients who were already on a daily aspirin regimen before their operations.
But significantly more patients in the aspirin group experienced major bleeding than those who took the placebo -- 230 patients versus 188 in the placebo group.
The findings contradict previous studies that found that aspirin could help prevent heart attacks after surgery. But those studies were smaller, the researchers noted, or looked at surgical outcomes after treatments had already been assigned, making their results less definitive.
Researchers say it could be that aspirin does prevent heart attacks caused by blood clots, but when it's given to patients in addition to other blood thinners, as is often the case, the bleeding risk cancels any benefit.
Bleeding can also cause heart attacks, explained study author Dr. P.J. Devereaux, an associate professor of epidemiology and biostatistics at McMaster University in Ontario, Canada. A sharp drop in blood pressure can seriously stress the heart, sending it into cardiac arrest.
"The perioperative period is a tricky period in terms of balancing these competing physical effects that are going on," Devereaux said.
"We should stop aspirin during the perioperative period, because we're only putting patients at risk without an apparent benefit," he added.
"Perioperative period" refers to the time shortly before, during and shortly after surgery.
For patients who take a low dose of aspirin each day to prevent either first or second heart attacks, Devereaux said the study found that it's safest to resume that regimen eight to 10 days after surgery, since that's when bleeding risk subsides.
For more tips on getting ready for surgery, visit the U.S. National Institute on Aging.