Better Tools for Predicting Post-Surgery Risk of Atrial Fibrillation

A simple CHADS2 score, along with records about ongoing use of certain medications, may help physicians predict the risk that individual patients will develop atrial fibrillation after thoracic or vascular surgery.

Mayo Clinic researchers analyzed records from 1,566 patients who underwent such procedures between 2003 and 2013 and found that 221 (14.1%) developed postoperative atrial fibrillation.

They then compared those who did and did not develop atrial fibrillation and found, via a single-variant analysis, that each 1-unit increase in a patient’s CHADS2 score was associated with a 22% greater atrial fibrillation risk.

This relationship survived subsequent efforts to adjust for potential confounding factors such as daily fluid balance, electrolyte values, intraoperative and postoperative vasopressor and inotrope requirements, length-of-surgery, blood transfusion, and resumption of ongoing cardiac medications.

Those efforts, however, uncovered several more significant, independent predictors of postoperative atrial fibrillation risk.

The largest among those independent risk factors was the preoperative use of beta-blockers (hazard ratio [HR], 2.04; 95% confidence interval [CI], 1.44-2.90).

Study team members, who presented their findings at the Society of Critical Care Medicine’s 44th Critical Care Congress, were surprised find increased risk associated with the use of medications that typically reduce atrial fibrillation risk. The most likely explanation, they believe, is that high-risk patients tend to use beta-blockers.

The only other pharmaceutical risk factor they found was preoperative use of calcium-channel blockers, which was associated with considerably lower risk of postoperative atrial fibrillation (HR, 0.67; 95% CI, 0.49-0.93).

The last 2 risk factors — SOFA scores 1 day after operations and intraoperative fluid administration — were both associated with increased incidence of atrial fibrillation. Each 1-unit increase in the former was associated with an 8% increase in atrial fibrillation risk (95% CI, 1.03—1.12), while every 1,000 ml of the later was associated with a 3% increase in atrial fibrillation risk (95% CI, 1.01–1.06)

The researchers hoped their results would give hospitals a simple-but-effective tool for predicting which 10% to 20% of their vascular surgery patients and thoracic surgery patients would go on to develop postoperative atrial fibrillation.

CHADS2 scores are easy to calculate, they noted, a simple matter of adding points for each of 5 risk factors that apply to a particular patient: Congestive heart failure, Hypertension, Age, Diabetes mellitus, and Stroke or TIA or thromboembolism.

The index was developed to predict the risk of stroke in patients who already have atrial fibrillation, but subsequent research found that it could also help predict the risk of postoperative atrial fibrillation in patients who undergo cardiac surgery.

There is, at present, no tool that is widely used to predict the occurrence of postoperative atrial fibrillation in patients who undergo vascular or thoracic surgery, even though atrial fibrillation ranks among the most common complications of both procedures.

There are, however, guidelines from the American Association for Thoracic Surgery designed to minimize the total number of patients who go on to develop postoperative atrial fibrillation, several of them supported strongly by research but “underused” in clinical practice:

• Patients taking beta-blockers before thoracic surgery should continue them (though perhaps at reduced doses) after their operations to avoid beta-blockade withdrawal
• Doctors should consider intravenous magnesium supplementation to prevent postoperative atrial fibrillation when serum magnesium level is low or if they suspect that total body magnesium is depleted
• Preventive administration of medications such as diltiazem or amiodarone may be reasonable for some patients who face increased risk of atrial fibrillation but it is not recommended for all such patients

Minimizing cases of postoperative atrial fibrillation is important, according to at least 1 recent study, because the seemingly temporary condition can more than double the chances that patients will go on to suffer strokes over the next 12 months.