The authors examined by 24-hour Holter monitoring the ECG in 20 patients treated on account of primary hypothyroidism with thyroid hormones. The patients were divided, with regard to the presence or absence of manifest ischaemic heart disease, into two groups which differed significantly as to the mean age of patients and the minimal R-R interval. In both groups diffuse ectopia was found without persisting activity except for one patient after myocardial infarction with relapsing ventricular tachycardia, organic sinoatrial blocks were found in two patients, an organic atrioventricular grade II block in one female patient and a functional (vagotonic) atrioventricular block of a higher grade in one female patient. Significant depressions of the ST segment, mostly of the asymptomatic type, were recorded in 55% of the patients, not differing in intensity and number of delevelings in positive patients of both groups. Comparison of mean circadian heart rates in relation to the type of substitution treatment revealed a minor tachycardic effect of one-component preparations containing levothyroxine only.

Keywords: Electrocardiography, Ambulatory; Female; Heart Rate /drug effects/; Humans; Hypothyroidism /drug therapy/; Middle Aged; Thyroid Hormones /therapeutic use/