Activation of electrical triggers of atrial fibrillation in hyperthyroidism.

Context: A shortening of the atrial refractory period has been considered as the main mechanism for the increased risk of atrial fibrillation in hyperthyroidism. However, other important factors may be involved. Objective: Our objective was to determine the activity of abnormal supraventricular electrical depolarizations in response to elevated thyroid hormones in patients without structural heart disease. Patients and Design: Twenty-eight patients (25 females, three males, mean age 43±11 yr) with newly diagnosed and untreated hyperthyroidism were enrolled in a prospective trial after exclusion of heart disease. Patients were followed up for 16 ± 6 months and studied at baseline and 6 months after normalization of serum TSH levels. Main Outcome Measures: The incidence of abnormal premature supraventricular depolarizations (SVPD) and the number of episodes of supraventricular tachycardia was defined as primary outcome measurements before the start of the study. In addition, heart rate oscillations (turbule...