The Curious Clinicians [Archive] Irregularly Irregular
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Mar 5, 2026 Why check TSH in new atrial fibrillation and what thyroid levels do to the heart. Data linking subclinical and overt hyperthyroidism with increased AF risk. How T3 alters sympathetic tone, atrial electrophysiology, and pulmonary vein triggers. Long-term inflammation and fibrosis as possible drivers of sustained arrhythmia. Interactions with levothyroxine and amiodarone, plus treatment uncertainties.
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Hyperthyroidism Markedly Increases AFib Risk
- Overt hyperthyroidism raises atrial fibrillation risk about three to sixfold.
- Risk rises continuously with free T4: high-normal free T4 ~1.45 HR and overt disease markedly higher.
T3 Creates An Afibogenic Hemodynamic Milieu
- Acute T3 exposure increases sympathetic sensitivity and heart rate, shortening atrial effective refractory period.
- Shortened refractory period plus ectopic triggers enables reentry/rotor waves that sustain AFib.
Thyroid Hormone Directly Triggers Pulmonary Vein Ectopy
- T3 acts directly on atrial and pulmonary vein myocytes to increase early and late afterdepolarizations.
- Rabbit cell experiments showed T3-incubated pulmonary vein cells developed spontaneous afterdepolarizations absent in controls.