Patients with diabetes who have blockages in their coronary arteries have notably better odds of survival if the heart problem is resolved with bypass surgery rather than angioplasty, new Canadian research shows.
The study published on Friday in the medical journal Lancet Diabetes and Endocrinology shows that the mortality rate is 33 per cent lower for bypass than angioplasty five years after the procedure.
The mortality rate was similar with either procedure for patients without diabetes. But the rate of stroke is slightly higher during bypass surgery than angioplasty, the study shows.
The findings are important because there is debate over the best method of treatment for blocked arteries. Angioplasty is quicker, cheaper and less traumatic for patients because it requires only a small incision, but it often has to be redone or followed by surgery if the blockages recur. Bypass operations are more invasive and costly, but can deal with blockages more thoroughly.
Over the years, guidelines have been developed saying, essentially, that patients with more serious heart disease should get a bypass, but they are divided on the best approach for low-risk patients. About one-quarter of all procedures to clear arteries – known as revascularization – are done on patients with diabetes, the group that was the focus of this new research.
"It's pretty clear that people with diabetes are better served by bypass," said Subodh Verma, a cardiac surgeon at St. Michael's Hospital in Toronto and principal author of the paper. "We hope this research will influence practitioners to make the right choice."
Angioplasty, which is known formally as primary percutaneous coronary intervention (PCI), is a simple operation in which a balloon catheter is inserted into an artery in the groin, then snaked up to restore blood flow to the heart by pushing out the blockage. In most cases, a stent – a device that holds the artery open – is also inserted.
Bypass surgery, or coronary artery bypass graft (CABG) in medical parlance, is a surgical procedure that uses an artery from the chest or a portion of a vein from the leg to channel blood around a narrowed segment of a coronary artery.
Research published last year in the Canadian Medical Association Journal show that rates of PCI and CABG vary dramatically among hospitals.
"There's not really any good reason for the variation," said David Latter, division head of cardiovascular surgery at St. Mike's and co-author of the paper. "It depends on the culture of institutions."
Stated more bluntly, politics and economics play a key role. Cardiologists perform angioplasty and stenting, while cardiac surgeons do bypasses. Many specialists have a bias toward the procedure they know best – and for which they would be paid. Cardiologists tend to have more contact with heart patients, and cardiac surgeons complain that, as a result, too many angioplasties are performed in cases where a bypass would be more appropriate.
Dr. Latter said he hopes the new study will help institutions make more evidence-based choices. The authors of the new paper also recommend that a team and the patient decide between CABG and PCI.
The new study is a meta-analysis, in which existing research is compiled and analyzed. In this instance, Dr. Verma and his team used the combined results of 14 studies involving a total of 6,389 patients that compared CABG and PCI head to head. About half the patients who underwent revascularization had diabetes.
Five years after the procedure, 6.8 per cent of diabetic patients who had undergone bypass surgery had died, compared to 10.9 per cent of patients who had angioplasty.
For people without diabetes, the mortality rate was virtually identical for both groups.
The research does not explain why patients with diabetes do better with bypasses, but Dr. Verma said the likely explanation is that diabetics have "more diffuse disease" – meaning they have more blockages in their arteries. Angioplasty tends to zero in on one spot; with surgery, several blood vessels can be bypassed.
The one downside of bypass surgery is that it resulted in more non-fatal strokes. That is because during the procedure, the heart is stopped and a mechanical pump is used, which can lead to more clotting.
About 2.5 million Canadians have diabetes, a disease characterized by high levels of blood glucose that can cause circulatory, heart and kidney problems. About 40,000 people a year die of diabetes in Canada; it is also the leading cause of amputations and blindness.
An estimated 1.6 million Canadians have cardiovascular disease. Approximately 70,000 people a year in Canada die of cardiovascular disease – including heart attacks, heart failure and stroke.