Development of Atrial Fibrillation After Cardiac Surgery Predicts Significantly More Morbidity

New-onset atrial fibrillation (AF) after surgery still occurs frequently among cardiac surgery patients, despite advances in therapeutic options, and leads to significantly more morbidity.

“Atrial fibrillation is the most common postoperative complication in cardiac surgery, has numerous negative effects on patients and is very costly for the health care system as a whole,” said Jean Abboud, MSc, a medical student and research assistant at the University of Ottawa Heart Institute, in Ontario.

“Some of the mechanisms that we’re aware of include adrenergic stimulation, systemic inflammation, or autonomic activation in the intraoperative or postoperative period,” he said. The study sought to describe the epidemiology and outcomes of cardiac surgery patients with no previous history of AF.

To that end, he and his co-investigators enrolled 1,416 adult patients into the prospective, observational cohort study.

All patients underwent nonemergent coronary artery bypass grafting and/or valve surgery at the institution between 2014 and 2015.

“Our patients were an average of 66 years old, and primarily men,” he noted. “The majority were being treated for hypertension.” Patients with a history of AF were excluded. “We also didn’t include patients who underwent aortic arch procedures,” he said.

Associated Predictive Variables

As Mr. Abboud reported at the 2016 annual meeting of the Canadian Anesthesiologists’ Society (abstract 151541), a total of 486 patients (34.3%) developed new-onset postoperative AF, which was defined as an event that required any form of in-hospital treatment. “This rate is also similar to the quoted rates in the latest literature. Also, a quarter of these patients had a recurrence of atrial fibrillation after they were treated,” he said.

“We selected 31 predictive variables based on a literature review and expert panel consultation,” Mr. Abboud explained.

When comparing patients who developed postoperative AF with those who did not, the investigators found the former were older (69.3±9.7 vs. 64.1±11.4 years; P<0.001), had lower creatinine clearance (84.7±33.6 vs. 93.7±38.8 mL/min; P<0.001), were more likely to undergo valve surgery (47.5% vs. 35.6%; P<0.001) and had larger left atrial volumes (34.7±13.0 vs. 31.4±11.9 mL/m²; P<0.001) than the other group.

Variables that were not associated with new-onset AF included obesity, diabetes, peripheral vascular disease, perioperative anemia, history of smoking and history of hypertension.

“We also investigated intraoperative details to look for associations with development of atrial fibrillation, and the only ones we found were with patients who had blood transfusions such as platelets, red blood cells or fresh frozen plasma, as well as patients who required bypass times of more than 100 minutes,” Mr. Abboud said.

Perhaps not surprisingly, the incidence of postoperative complications was found to be significantly higher in the postoperative AF group than the unaffected patients. Complications included:

• readmission to the ICU (6.4% vs. 1.1%;P<0.001),
• reintubation (4.5% vs. 1.3%;P<0.001),
• intubation more than 48 hours (5.8% vs. 1.6%;P<0.001),
• cardiogenic pulmonary edema (5.1% vs. 1.1%;P<0.001),
• time spent in the ICU (3.0±5.2 vs. 1.9±3.7 days;P<0.001),
• hospital length of stay (12.5±12.4 vs. 7.9±7.1 days;P<0.001),
• acute renal injury (20.4% vs. 8.4%;P<0.001), and
• need for one unit or more of red blood cells, platelets or fresh frozen plasma (16.0% vs. 11.8%;P<0.05).

Differences found between groups, however, were not significant for stroke (1.4% vs. 0.5%), seizure (1.4% vs. 0.5%), malignant arrhythmia (4.9% vs. 3.0%), gastrointestinal bleeding (1.0% vs. 0.5%), heart block (4.5% vs. 3.0%) and death (1.2% vs. 0.9%).

“In conclusion,” Mr. Abboud said, “atrial fibrillation remains the most common postoperative complication in cardiac surgery. We hope that the data we generated from this study can ultimately be used to lower that rate and reduce its impact on patients.

“Going forward,” he added, “we’ve developed a bedside prophylaxis score that we’re going to start testing in a multisite interventional trial.”

“Did you track the use of beta-blockers?” asked Daniel Bainbridge, MD, associate professor of anesthesia and perioperative medicine at Western University’s Schulich School of Medicine & Dentistry, in London, Ontario. “And when you defined the use of antiarrhythmics, did that include beta-blockers? Because frequently that is one of the first lines of choice.”

“The antiarrhythmics did not include beta-blockers,” Mr. Abboud replied. “So 68% of the cohort were already on beta-blockers at the start of the study, and this was not associated with an increase afterward. However, when beta-blockers were restarted and escalated postoperatively for postoperative atrial fibrillation, this was counted as a treatment.”