Utility of routine thyroid-stimulating hormone determination in new-onset atrial fibrillation in the ED.

Introduction: Hyperthyroidism is a relative uncommon but important cause of atrial fibrillation. The aim of this study was to investigate the utility of routine thyroid-stimulating hormone (TSH) determination in the emergency department (ED) in patients presenting to the ED with stable, new-onset atrial fibrillation. We derive a set of clinical criteria in which TSH is likely to be normal and therefore thyroid function evaluation deferrable to a different time from ED visit.

Methods: Cross-sectional observational study in a university hospital. Thyroid-stimulating hormone was measured in all patients admitted to the ED observational unit for new-onset atrial fibrillation in a 30 consecutive months' period. Patients' clinical characteristics and treatment received in the ED were recorded. Recursive partitioning analysis technique was used to determine which predictors were associated with a TSH level less than 0.35 μIU/mL.

Results: Of 433 patients enrolled, 47 (10.8%) had a low TSH. Thyroid-stimulating hormone highly correlated with FT3 and FT4 levels (P < .001) confirming its good predictive value as screening tool. Recursive partitioning analysis showed that previous thyroid disease (P < .01), stroke/transient ischemic attack (P < .01), and hypertension (P = .10) were associated with low TSH. The final model had sensitivity of 93% and specificity of 31%, corresponding to a negative likelihood ratio of 0.02 (0.01-0.07).

Conclusion: Hyperthyroidism is present in nearly 10% of new-onset atrial fibrillation. Although thyroid function screening is recommended in all patients, a simple model that included previous thyroid disease, stroke, and hypertension might help to identify those patients at high risk (low TSH) in the ED.