PHOENIX – For every unit increase in baseline CHADS2 score, the risk of postop atrial fibrillation increases by 17%, according to a retrospective chart review of 1,550 adults who had major vascular or thoracic surgery at the Mayo Clinic in Rochester, Minn.
On multivariate analysis, postop day 1 Sequential Organ Failure Assessment score (HR 1.08, 95% CI 1.03-1.12, per unit increase) and cumulative fluid balance (HR 1.03, 95% CI 1.01-1.06, per 1,000 mL) also correlated with the risk for new-onset atrial fibrillation (AF).
Baseline calcium channel blockers protected against new-onset AF (HR 0.52, 95% CI 0.37-0.73), but, paradoxically, the risk increased with baseline (HR 1.78, 95% CI 1.24-2.56) and postop (HR 1.44, 95% CI 1.05-1.99) beta-blocker use.
The relationship of CHADS2 to new-onset AF (HR 1.17, 95% CI 1.04-1.31) could prove handy in the surgical ICU because “everyone is familiar with it, and it’s easy to calculate.” CHADS2 (heart failure, hypertension, age, diabetes, prior stroke) has also recently been shown to predict AF after cardiac surgery, said lead investigator Kirstin Kooda, Pharm.D., a critical care pharmacist at Mayo.
The beta-blocker finding was a surprise, since beta-blockers are a standard AF treatment, Dr. Kooda said at the Critical Care Congress, sponsored by the Society for Critical Care Medicine. About 80% (175) of new-onset AF patients were on baseline beta-blockers, versus about 68% (892) who did not develop AF. Patients using beta-blockers received them the morning of surgery, and resumed them a median of 7 hours afterward. There were no significant differences in heart rates during surgery.
The team excluded patients with any history of AF and censored patients if they developed it, so the drugs’ use probably wasn’t related to a concern about the condition. Just under 70% of patients in both groups had baseline hypertension, another indication for the drugs.
Even so, the finding is probably real given the number of patients in the study. Most likely, the drugs were markers for additional risk factors not captured in the study, Dr. Kooda said.
Overall, 112 (20.7%) of the 540 thoracic patients and 107 (11%) of the 1,010 vascular patients developed new-onset AF a median of 55 hours after surgery. The incidence difference and timing are in line with previous reports.
The mean age in the AF group was 70 years, and in the non-AF group it was 66 years. In both, 65% were men, 5% had heart failure, 30% had diabetes, and 10% had prior strokes. Patients with pacemakers and recent myocardial infarctions – also possible settings for beta-blockers – were excluded from the trial.
The majority of the vascular cases were open aortic aneurysms, aortic bypasses, and thrombectomies or endarterectomies of central arteries. Most of the thoracic surgeries were lobectomies, pneumonectomies, and wedge or chest wall resections.