Free thyroxine within the normal reference range predicts risk of atrial fibrillation

Abstract

Introduction: Hyperthyroidism is a known precipitating factor for atrial fibrillation (AF). However, recent reports have suggested an increased risk of AF with free thyroxine (fT4) levels even within the upper reference (normal) range. We sought to test whether higher fT4 levels within the reference range are associated with an increased risk of AF.Methods and Results: All patients in the Intermountain Healthcare electronic medical record database with an fT4 level not on thyroid medication were included. The reference range of fT4 was divided into quartiles (Q), and associations with prevalent and incident AF were assessed by multivariable regression. Similar analyses were performed for thyroid stimulating hormone (TSH) and total and free T3. A total of 174 914 patients were included and followed for 7.0 ± 4.9 years. Of these, 7.4%, 88.4%, and 4.2% had fT4 levels below, within, and above the reference range. As expected, prevalent AF was greater with elevated fT4. However, gradients also were noted within the reference range, comparing Q4 to Q1, for prevalent AF (adjusted odds ratio 1.4, P < .0001) and incident AF (adjusted hazard ratio 1.16, P < .0001). In contrast, no relationship with AF prevalence and incidence was noted for total and free T3 within their reference ranges, and the pattern for TSH was uninformative.Conclusion: Higher fT4 levels within the reference range were associated with an increased prevalence and incidence of AF. These findings in a large dataset prospectively validate earlier reports and may have important implications, including a redefinition of the normal range and fT4 targets for replacement therapy.

High-Normal Thyroid Function and Recurrence of Atrial Fibrillation after Catheter Ablation: A Prospective Observational Study

“…Patients with long-standing overt hyperthyroidism with an increased cardiac output can predispose to AF occurrence [11]. It has been demonstrated that even subclinical hyperthyroidism is associated with an increased risk of AF [12-14]. Recent studies indicated that patients with a history of thyroid dysfunction (both hyperthyroidism and hypothyroidism) had a higher incidence of arrhythmia recurrence after AF catheter ablation [15, 16].…”

Liothyronine and Desiccated Thyroid Extract in the Treatment of Hypothyroidism

“…The first is an analysis of 174,914 patients followed for 7.0 -4.9 years. It revealed that the incidence and prevalence of AF was greater with elevated serum fT4 levels, even within the normal reference range, but no relationship was noted for serum total T3 and fT3 within their normal reference ranges (62). The second study is an analysis of 55,114 individuals with AF and 482,295 referents.…”

Impact of thyroid disease in patients with atrial fibrillation: Analysis from the JoFib registry

“…Atrial fibrillation (AF) is the most common cardiac arrhythmia worldwide, affecting more than 30 million persons all over the globe [ 1 ]. Characterized by ever increasing prevalence and incidence rates, AF contributes significantly to morbidity and mortality through increased risk of stroke, heart failure and hospitalizations [ 2 ]. In particular, AF increases the risk of stroke by 5 folds; these strokes are of greater severity and lethality than those of their non-AF counterparts [ 2 ].…”

“…Characterized by ever increasing prevalence and incidence rates, AF contributes significantly to morbidity and mortality through increased risk of stroke, heart failure and hospitalizations [ 2 ]. In particular, AF increases the risk of stroke by 5 folds; these strokes are of greater severity and lethality than those of their non-AF counterparts [ 2 ]. Despite its slightly increased prevalence in men, AF's adverse complications are more pronounced in women [ 3 ].…”