Severely obese coronary artery bypass patients are three times more likely to develop an infection shortly after surgery and stay in the hospital longer, according to new research in Journal of the American Heart Association.

Coronary artery bypass surgery redirects blood flow to the heart around clogged heart arteries.

“Based on the results of this study it appears that addressing infection risk might be an effective strategy to decrease the length of stay for patients with obesity who undergo coronary artery bypass surgery,” said Mary Forhan, Ph.D., the study’s senior author and assistant professor in the Department of Occupational Therapy, Faculty of Rehabilitation Medicine, at the University of Alberta in Edmonton, Canada.

Using a Canadian database of heart patients, the new study examined how a racially and ethnically diverse group of 7,560 patients fared after having bypass surgery in Edmonton between April 2003 and March 2014.

Patients were divided into five groups based on their body mass index, a measure of body size based on weight and height:

  • Normal weight (BMI of 18.5-24.9)
  • Overweight (25-29.9)
  • Obesity class I (30-34.9)
  • Obesity class II (35-39.9)
  • Obesity class III (40 or higher)

For example, a 5-foot-4 woman would be at a normal weight at 110 to 145 pounds; overweight at 145 to 174 pounds; and obese at 174 pounds or more. At 232 pounds, she would have a BMI of 40, the threshold for severe obesity.

Compared with patients at normal weight, those with severe obesity tended to be younger; were more likely to have diabetes, elevated cholesterol/triglycerides, high blood pressure or lung disease; and were more likely to have undergone coronary angioplasty, a surgical procedure to open clogged arteries in the heart.

Researchers also found:

  • Patients with severe obesity were 56 percent more likely to have complications within a month of surgery, and those classified as having moderate (class II) obesity had a 35 percent higher risk.
  • The median hospital stay — the point where half the patients stayed fewer days and half stayed more — was a day longer for severe obese patients than for patients of normal weight.
  • Severe obese patients with diabetes who experienced an infection had hospital stays 3.2 times longer than patients without either condition.

The findings emphasize a need for attentive care in bypass patients with diabetes, Forhan said. “We know that wound healing in general is affected by poorly controlled glucose levels, and that adipose (fat) tissue may take longer to recover from trauma, such as the kind that occurs during surgery. Therefore, as is recommended for all patients, efforts to ensure good glycemic control for patients with diabetes pre- and post-bypass are important.”

It’s not clear why these patients are more likely to develop infections, Forhan said.

“We need further study that includes ways of preventing infection using evidence-based methods, and determining if such methods meet the needs of coronary artery bypass patients with moderate to severe obesity,” she said.

Each year almost 400,000 Americans undergo coronary artery bypass. About seven in 10 U.S. adults age 20 or older are classified as overweight or obese, according to the Centers for Disease Control and Prevention.