Thyrotoxicosis in institutionalized elderly patients with atrial fibrillation.

We hypothesized that hyperthyroidism would be an infrequent cause of atrial fibrillation in older persons because atherosclerotic, hypertensive, and degenerative heart disorders are more prevalent with aging. We determined the cardiac rhythm and thyroid status of 316 patients older than 65 years of age residing in a nursing home. One (11%) of the nine elderly men and five (31%) of the 16 women with atrial fibrillation had laboratory evidence or a history of hyperthyroidism. The elderly patients with cardiac rhythms other than atrial fibrillation (n = 291) had only a 1.7% prevalence of hyperthyroidism. The analysis for elderly women demonstrated a statistically significant association between atrial fibrillation and hyperthyroidism, but the association was not statistically significant for men. These findings indicate that hyperthyroidism is common in institutionalized elderly women with atrial fibrillation.