Bradyarrhythmia as a presenting feature of subclinical hyperthyroidism.

In subclinical hyperthyroidism, thyroid-stimulating hormone (TSH) levels are suppressed below normal range but serum-free thyroxine and free triiodothyronine levels are within normal range. The clinical manifestations can be highly variable and patients mostly remain undiagnosed. Sinus tachycardia, atrial premature beats and atrial fibrillation are the reported tachyarrhythmias in such patients. Bradyarrhythmias are typically not reported in patients with subclinical hyperthyroidism. We present here a case of subclinical hyperthyroidism where symptomatic second degree atrio-ventricular block (Wenckebach) was the sole presenting feature.