The background of the study. Atrial fibrillation is a frequent manifestation of hyperthyroidism, but its reported frequency has varied widely, and predisposing factors are not well understood. This study determined the factors associated with atrial fibrillation in a large group of patients with hyperthyroidism.
How the study was done. All patients with a hospital discharge diagnosis of hyperthyroidism from 1977 through 1999, and all patients with an outpatient diagnosis of hyperthyroidism from 1995 through 1999 were identified in the Danish National Registry of Patients. All patients with a diagnosis of atrial fibrillation were similarly identified. Data on hypertension, coronary heart disease, valvular heart disease, heart failure, and diabetes mellitus before or at the time of diagnosis of hyperthyroidism also were obtained.
The results of the study. There were 40,628 patients with hyperthyroidism (34,513 women [85 percent], 6115 men [15 percent]); 48 percent were aged 20 to 59 years, and 52 percent were 60 to 89. Five percent had hypertension, 7 percent coronary heart disease, 1 percent valvular heart disease, 4 percent heart failure, and 4 percent diabetes.
Among the patients with hyperthyroidism, 3362 (8 percent) had atrial fibrillation; they included 2621 of the women [8 percent], and 741 of the men [12 percent]). The frequency of atrial fibrillation increased progressively with age, ranging from 0.3 percent among the patients aged 20 to 29 years to 19 percent of those 80 to 89. Other risk factors for atrial fibrillation, in addition to male sex and increasing age, were heart failure and coronary and valvular heart disese.
The conclusions of the study. Atrial fibrillation is more common in men than in women with hyperthyroidism, and its frequency increases markedly with age.
The original article. Frost L, Vestergaard P, Mosekilde L. Hyperthyroidism and risk of atrial fibrillation or flutter: a population-based study. Arch Intern Med 2004;164:1675-8.