| Colzani et al., Pisa, Italy, measured QT interval corrected for heart rate (QTc) in 12 patients with hyperthyroidism (mean age 47.5 years) before and after treatment and in 9 patients (mean age 49 ± 6 years) after total thyroidectomy and I-131 ablation for thyroid carcinoma, when hypothyroid 6 weeks after withdrawal of T4 (mean TSH 75mU/L) and during T4 administration (mean TSH 0.16mU/L). Sixteen healthy volunteers (mean age 34 ± 2 years) formed the control group. In addition plasma norepinephrine (NE) values were measured. NE levels were elevated in the hypothyroid patients vs controls, p < 0.01, while being normal in the hyperthyroid subjects. QTc was increased in the hypothyroid group vs the value when patients were treated, p < 0.01, and controls, p < 0.01). In hyperthyroid patients QTc was increased when untreated vs when patients were euthyroid, p < 0.02. QTc and vs. controls p < 0.01. In treated hyperthyroids, QTc was not different from controls. In untreated hyperthyroid patients a positive correlation was found between QTc and plasma free T3. The authors conclude that hyperthyroidism and acute hypothyroidism are risk factors for ventricular arrhythmias. Biondi et al., Naples and Catanzaro, Italy, assessed cardiac performance by complete Doppler- echocardiography and 24 hours Holter-tape registration in 23 patients with subclinical hyperthyroidism (SH) and compared results with a control group of 30 normal subjects (C). They found an increased heart rate (82 ± 6 vs 71 ± 8 beats per minute, p < 0.01) in SH vs C. No significant differences were observed in supraventrical or ventrical arrhythmias. However, a significant increase in left ventricular mass due to an increase of septal and posterior wall thickness was present in SH. Fractional shortening and circumferential fiber shortening was increased in SH. The authors conclude that the results support prompt treatment of SH. (Comment: Although this report shows an effect of SH on cardiac tissue and function, it is still not known if these changes are of pathologic significance. The finding that there are no increased arrhythmias in SH is in agreement with the report of Van de Wetering et al., Thyroid International, 5, 1999. I agree that treatment for SH is certainly an option, as I can not imagine that an increased basal heart rate would not have some consequences on the long run). |
