[Thyrotoxicosis and coexistent diseases in atrial fibrillation.]

To evaluate the prevalence of thyrotoxicosis and coexistent diseases in patients with atrial fibrillation admitted to a general medicine ward.

All patients with the discharge diagnosis of atrial fibrillation were studied. The study design was retrospective for the years 1993-1994 and prospective from April 1995 through December 1997. Information on thyroid function tests was obtained from medical records in the retrospective part, but TSH, T4 and T3 were measured for patients admitted during the prospective part. Coexistent diseases were recorded.

Atrial fibrillation was diagnosed in 167 patients (58 in the retrospective part and 109 in the prospective part). Males were predominant (59.3%) and the average age was 73.7 years (span 26-100). Adequate information on thyroid function tests was available for 135 patients (58.6% of the retrospective part and 92.7% of the prospective part). 24 (17.8%) had abnormal thyroid function tests, predominantly women (71%). Ten had an isolated elevation of TSH, seven an isolated depression of TSH, two hypothyroidism and five other abnormalities. Hypertension was the most common coexistent disease (76 of 167 patients (45.5%). Ischemic heart disease was found in 44 (26.3%) and valvular heart disease in 27 (16.2%). No known coexistent disease was found in 32 (19.2%).

1) Thyrotoxicosis is rare in patients with atrial fibrillation who are admitted to a general medicine ward. Routine measurement of thyroid function tests in this patient population is therefore not warrented. 2) Unspecific abnormalities of thyroid function tests are common and are most likely due to diseases outside the thyroid gland or medications. 3) Hypertension, ischemic heart disease and heart valve disease are the most common coexistent diseases in this group of patients.