Study: Obesity associated with risk of heart surgery complication

Being obese can raise your risk of developing a dangerous heartbeat irregularity following cardiac surgery, a study published in the journal Circulation has found.

While obesity has previously been linked in nonsurgical patients to atrial fibrillation - irregular beating in the heart's upper chambers - and heart surgery is also known to increase the risk, until now it hasn't been clear whether people who are obese face an even higher risk of developing this condition after surgery.

"New onset AF (atrial fibrillation) remains the most frequent postoperative complication of cardiac surgery, and contributes substantially to increased morbidity, resource utilization, and even early and possibly late deaths," write lead author Dr. Anoar Zacharias and colleagues.

Atrial fibrillation can be dangerous because it reduces the efficiency with which the heart pumps blood, increasing the risk that blood can pool in the atrium where it can form a blood clot. The clot can then travel to the brain and cause a stroke.

Previous research has found age, history of atrial fibrillation and high blood pressure to be among the factors that can increase the risk of developing atrial fibrillation after heart surgery. This study adds yet another risk factor to the list.

"The primary finding in the present study is that we have demonstrated, for the first time, the existence of a strong independent association between increasing body size (especially obesity) and new-onset postoperative AF in cardiac surgery patients," the authors say.

In the study, Zacharias' team of researchers looked at data from 8,051 people who had undergone heart surgery at two hospitals between 1994 and 2004. The participants were 64 years old, on average, and had no history of atrial fibrillation.

About 39% of the participants were considered obese, with a BMI (body mass index) greater than 30. After surgery, 22.5% of them developed atrial fibrillation.

After adjusting for a number of variables, obesity was found to be associated with an increased risk of developing atrial fibrillation following surgery, with a greater risk found as BMI increased. For example, people who were overweight (BMI between 25 and 30) or in the lowest category of obesity (BMI between 30 and 35) faced an 18% and 36% increase in risk, respectively, compared to those who were normal or underweight . Those who were the most obese (BMI greater than 40) faced the highest risk of developing atrial fibrillation, a 139% increase over the control group.

Among the reasons why obesity could be associated with this increased risk, the researchers speculate, is that left atrial enlargement - a known precursor to atrial fibrillation - is strongly associated with increasing BMI. However, because the researchers had no access to data on left atrium size, further investigation would be required to determine whether this factor plays a role in the risk increase.