[Arrhythmia profile and heart rate in hyperthyroidism].

Arrhythmia profiles and heart rates, obtained by 24-hour ECG monitoring, were analysed in 48 patients with hyperthyroidism before (T3 level: 331 +/- 108 ng/100 ml, heart rate: 95 +/- 13/min), during (T3 level: 202 +/- 98 ng/100 ml, heart rate: 85 +/- 11/min) and after (T3 level: 149 +/- 41 ng/100 ml, heart rate: 79 +/- 9/min) antithyroid treatment. 50 persons in whom organic heart disease has been excluded by invasive and noninvasive tests served as controls. Only 6% of patients had repetitive ventricular arrhythmias (Lown group IV) before treatment (controls: 4%; P greater than 0.05). Supraventricular extrasystoles were common both before and after treatment (P less than 0.001), especially in elderly patients. The number of patients with supraventricular tachycardias decreased in the course of treatment from eleven to two. There was a clear correlation between the T3 level and nocturnal heart rate (r = 0.74; P less than 0.001). A day-night difference in heart rate (a ratio of greater than or equal to 1.10) was present in 43 patients and higher than in the controls (P less than 0.001). Thus with respect to ventricular arrhythmias hyperthyroid patients had a normal profile, but a marked tendency towards supraventricular arrhythmias which was partly age-related. Antithyroid treatment affected only the incidence of supraventricular tachycardias, while day-night differences in heart rate remained unchanged.