Nancy A. Melville

February 05, 2015

PHOENIX — The CHADS₂ index, developed to gauge stroke risk in patients with atrial fibrillation, can also predict postoperative afib in noncardiac patients undergoing thoracic or vascular surgery, according to a study presented here at the Society of Critical Care Medicine 44th Critical Care Congress.

This finding is important because there has been no prognostic tool to identify patients at risk, said study investigator Kirstin Kooda, PharmD, from the Mayo Clinic in Rochester, Minnesota.

"Atrial fibrillation is very common — probably the number 1 complication in many patients in the ICU — yet we haven't had anything to guide us on who is most at risk," Jose Pascual, MD, from the University of Pennsylvania in Philadelphia, told Medscape Medical News.

Postop atrial fibrillation is a potentially serious complication that occurs in approximately 10% to 20% of patients undergoing vascular and thoracic surgery. Known risk factors are type of surgery, age, baseline arrhythmia status, postop fluid status, and electrolyte abnormalities.

"It's difficult to make blanket statements about risk, especially across varied types of surgeries," Dr Kooda explained.

The CHADS₂ index takes into account congestive heart failure, hypertension, age, diabetes mellitus, and stroke. The index is an ideal risk assessment tool because it is easy to calculate, she added.

Previous research has shown that the index can be effective in predicting postop atrial fibrillation risk in cardiac surgery patients, so Dr Kooda and her colleagues investigated its value in noncardiac vascular and thoracic surgery patients.

They assessed patients with no history of atrial fibrillation who were undergoing noncardiac thoracic or vascular surgeries from 2006 to 2013.

Of the 1566 patients, 221 (14.1%) developed postoperative atrial fibrillation at a median of 55 hours after surgery.

On univariate analysis, the CHADS₂ score was significantly associated with the incidence of postop atrial fibrillation; for every unit increase in score, the hazard ratio was 1.22.

The association remained after a multivariate adjustment for factors such as daily fluid balance, electrolyte values, intraoperative and postoperative vasopressor and inotrope requirements, length of surgery, blood transfusion, and resumption of home cardiac medications.

Table. Factors Independently Associated With Postop Atrial Fibrillation

Factor Hazard Ratio 95% Confidence Interval
Preoperative beta-blocker use 2.04 1.44–2.90
Postoperative day 1 SOFA score (per unit increase) 1.08 1.03–1.12
Intraoperative fluid administration (per 1000 mL) 1.03 1.01–1.06
Preoperative calcium-channel blocker use 0.67 0.49–0.93

 

There was an association between the preoperative use of beta blockers and postop atrial fibrillation, which was a surprise, Dr Kooda pointed out. "This is counterintuitive, especially considering that the bulk of the literature reports a decreased risk of atrial fibrillation with beta blockers at baseline," she explained. "Our current hypothesis is that these are perhaps the patients with the highest percentage of risk factors at baseline."

This finding could also be related to a withdrawal effect from the drugs, said study investigator Arun Subramanian, MBBS, also from the Mayo Clinic in Rochester.

"It is well known that if patients suddenly stop beta blockers, they develop withdrawal, including an increase in heart rate and the development of chest pain," he told Medscape Medical News.

"Surgical patients, many times, do not take their medications while fasting for surgery. Also, postoperatively, bowel function slows down and beta blocker pills may not be well absorbed," he explained.

"I favor this explanation — that beta blocker withdrawal increases the risk of atrial fibrillation," Dr Subramanian said. "We are investigating this further."

The findings also suggest that limiting fluids in high-risk patients can reduce atrial fibrillation risk, he added. "We are already doing this for our thoracic surgery patients."

With the host of potentially serious problems associated with postop atrial fibrillation, the identification of risk factors can be beneficial on numerous levels, Dr Subramanian emphasized.

"When patients develop postop atrial fibrillation, they usually have to stay in the hospital longer for treatment and have a higher risk of morbidity and mortality," he said. "In addition, it increases the cost of care. These patients will need more intense monitoring, typically in an ICU-like setting, and IV infusions of medications for heart rate control."

"Our results are preliminary, but promising," Dr Subramanian said. "We have changed practice based on some of our findings."

This study offers valuable information on the potential of CHADS₂ in noncardiac surgery patients, said Dr Pascual. "What is great is that the authors looked at noncardiac surgery patients. People who have vascular surgery, for instance, often develop cardiac arrhythmias such as atrial fibrillation," Dr Pascual explained. "So the researchers chose an appropriate population."

And the relative simplicity of the CHADS₂ index makes it an appropriate tool, he added. "It's a novel use for this, and could be very useful for bedside doctors," he said. "If we can determine that patients are at high risk, we can prepare for it, so it could be very beneficial."

Dr Kooda, Dr Pascual, and Dr Subramanian have disclosed no relevant financial relationships.

Society of Critical Care Medicine (SCCM) 44th Critical Care Congress: Abstract 1. Presented January 18, 2015.

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