[Systematic ultrasensitive determination of thyroid-stimulating hormone in 50 cases of atrial fibrillation].

The incidence of hyperthyroidism in patients with continuous arrhythmia due to atrial fibrillation was evaluated prospectively by means of the "ultrasensitive" assay of thyroid-stimulating hormone (TSH). When the result was abnormal, free thyroxine fractions (FT4) and free triiodothyronine fractions (FT3) were measured, and in some cases a thyrotropin-releasing hormone (TRH) test and a thyroid gland scintigraphy were performed. Among 50 unselected patients with continuous arrhythmia due to atrial fibrillation, 12 had a low TSH baseline level. In 7 of them, high FT4 and/or FT3 levels provided evidence of hyperthyroidism. In the remaining 5 patients FT4 and FT3 levels were normal, but TSH response to TRH was suppressed and scintigraphy showed a high nodular or lobular uptake. In a control series of 50 age- and sex- matched subjects without thyroid disorders or dysrhythmia, TSH level was low in only one case with insufficient response to TRH, but the scintigraphic image did not suggest nodular hyperthyroidism. It is concluded that systematic TSH assays can detect those atrial fibrillations which are consecutive to, or aggravated by hyperthyroidism, even asymptomatic. We regard this assay as indispensable to evaluate continuous arrhythmia due to atrial fibrillation, even when an apparently causative underlying heart disease is present.