Abstract
BACKGROUND: Atrial fibrillation/flutter (AF) is the most frequent cardiac arrhythmia worldwide. It increases the risk for comorbidities and prompt management is thus important. One established risk factor for AF development is hyperthyroidism, and concomitant disease significantly impacts morbidity in these patients. Therefore, thyroid function testing is recommended in new-onset AF (NOAF) by the European Society of Cardiology. There are few studies examining the prevalence of previously undiagnosed hyperthyroidism in cases of NOAF, especially if diagnosed in the emergency department (ED). Furthermore, previous studies often relied upon thyroid stimulating hormone (TSH) levels to identify cases of hyperthyroidism, this approach is susceptible for diagnostic errors since TSH profiles can overlap in conditions like hyperthyroidism, non-thyroid illness, and central hypothyroidism (of which only the former is associated with AF). Because of this, it's essential to incorporate additional biomarkers for a more precise differentiation. PURPOSE: We aim to evaluate the prevalence of previously undiagnosed hyperthyroidism in a real-life NOAF population admitted to and diagnosed in the ED with a 2.5-years follow-up. Furthermore, we aim to interpret thyroid dysfunctions in relation to TSH as well as free thyroid hormone levels and other relevant biomarkers. METHODS: This retrospective registry-based cohort study included all patients attending the ED at a medium-sized hospital in Sweden during 2018 and 2020. Inclusion criteria: main diagnosis of AF (ICD I48) and ≥18 years old. Exclusion criteria: multiple visits, previous AF, abnormal thyroid function within the previous 2 years, and current thyroid hormone substitution. RESULTS: Patients from a total of 1020 ED visits were screened for eligibility. After exclusion, 325 patients with NOAF were included in the analysis. Of those, 106 (33%) and 232 (71%) had undergone thyroid function testing in the ED and by the end of the 2.5-years follow-up, respectively. We found no cases of hyperthyroidism in the ED and only two cases (1% prevalence) during the 2.5-years follow-up. CONCLUSIONS: In this real-life cohort we found modest thyroid testing rates in the ED, however, a majority of patients underwent testing during follow-up. Despite this, we found no cases of hyperthyroidism in the ED and only two cases during follow-up, this is considerably lower than previously reported and may raise a question whether all patients should undergo thyroid testing, or if thyroid testing should be directed towards those with a suspected thyroid disease. [Figure: see text]