The study found that diabetics who had bypass surgery were about 33 per cent more likely to be alive five years later than those who underwent a procedure to have the blockage opened with a stent.
In recent years, the number of cardiac bypass surgeries has declined as doctors have opted for the less invasive stenting procedure, where a tiny tube is threaded into place in the artery from a small incision in the patient's groin.
But questions have remained about whether stents are a good option for diabetics, who often have more blockages than other patients.
This study, which was led by doctors at Toronto's St. Michael's Hospital, pooled data from eight clinical trials to try to answer the question.
The authors say the substantial survival advantage of bypass surgery suggests it should be strongly considered for diabetics needing artery-opening procedures.
"It is a pretty significant effect. And it is kind of startling to think that there's still some debate about this when results like these kinds of significant differences are coming out," said Dr. David Latter, a cardiac surgeon and one of the authors of the study.
While the survival effect was large, the study did also find that diabetic patients who had bypass surgery were more likely — 1.75 times more likely — to have a non-fatal stroke in the five years after the procedure than those who had a stent inserted.
The authors suggested the increased risk of stroke was likely related to having undergone surgery and may have been linked to lower use of anti-clotting drugs in the surgical patients.
The work comparing the two revascularization procedures was published Thursday in the journal Lancet Diabetes and Endocrinology.
Dr. Gideon Cohen, head of cardiac surgery at Sunnybrook Health Sciences Centre in Toronto, said the study adds weight to an idea that has been coming into focus for awhile — that bypass surgery is a better route to go with diabetic patients.
In bypass surgery, the chest is opened and blocked sections of arteries are circumvented with grafted artery tissue.
"The challenge here is that you're pitting a very non-invasive procedure" — inserting a stent — "against the very invasive procedure," noted Cohen, who was not involved in the study.
Both surgeons suggested the way care is currently delivered may make it difficult to change practice with this group of patients, who make up about 25 per cent of the patients needing an artery-opening procedure in Canada.
But Latter said the study findings suggest practice should change.
When a patient has had a heart attack or a blockage is suspected because of chest pain, he or she has a test called an angiogram to look for blocked arteries. When one is spotted, it's not uncommon for a patient to be asked if he or she wants a stent inserted immediately.
Cohen said that while taking care of the blockage immediately is tempting and convenient, patients with diabetes should know the risks and benefits and long-term prospects before they make that kind of decision.
"Sometimes we don't give patients enough credit to make the most well-informed decisions," he said.
"But they have to be informed appropriately. They have to be given the option to come off the table and to speak to a surgeon if they wish to speak to a surgeon."
Cohen suggested, in fact, that the discussion about which route to follow and the pros and cons of both should take place before the test is done. "The discussion absolutely has to be had prior to the procedure."