Effects of L-thyroxine suppressive therapy on cardiac mass in patients with differentiated thyroid cancer

Patients with differentiated thyroid carcinoma (DTC) receive a life time l-thyroxine therapy in suppressive doses and may exhibit signs of cardiac hypertrophy. The aim of the study was to analyze the left ventricle mass parameters by echocardiography in patients treated with suppressive doses of thyroxine and to relate them to the possible occurrence of cardiac arrhythmias. Ninety four patients aged 19-70 years treated chronically with l-thyroxine were randomly chosen from the population of patients with DTC without concomitant diseases of circulatory system. They were divided into two subgroups according to the length of thyroxine therapy (< 60 months and > or = 60 months). Control group consisted of 41 healthy volunteers, aged 22-73 years. Heart muscle dimensions were measured by echocardiography. Left ventricle mass (LVM) and mass index (LVMI) was calculated. Electrocardiography according to Holter was carried out in 57 patients. The results of echocardiography in the whole group of patients did not differ significantly from the control group, although a tendency towards higher dimensions of the left ventricle was observed. No correlation of hormonal parameters, or thyroxine dose, with LVM or results of Holters ecg was noted. When patients were subdivided into two groups, according to the duration of therapy, significantly higher values of LVM (215 +/- 64 g versus 186 +/- 55; p < 0.05) and LVMI (114 +/- 31 g/m versus 102 +/- 23 g/m; p < 0.05) were observed in patients treated > or = 60 months in comparison to the control group. When results of Holter's ecg in patients with increased LVMI were analyzed, cardiac rhythm disturbances were stated in 50% of them, but most were of minor clinical relevance. Suppressive l-thyroxine therapy does not induce significant left heart hypertrophy during the first 5 years of treatment. Patients treated through a longer period of time should be controlled by echocardiography because of the increasing risk of the left ventricle hypertrophy and arrhythmia.