Abstract
Background: Subclinical hypothyroidism (SCH) is an apparently asymptomatic condition defined by increased serum thyrotropin (thyroid-stimulating hormone) concentrations, but normal serum free T3 and free T4 hormone levels. Thyroid hormones are known to affect the heart and vasculature. The effect of SCH on cardiovascular system is not much studied.

Aims and Objectives: The objectives of this study were to study the electrocardiogram (ECG) changes in a group of newly diagnosed subclinical hypothyroid females and to compare the ECG changes in subclinical hypothyroid females with normal healthy euthyroid individuals.

Materials and Methods: We studied 30 non-pregnant females with primary SCH in the age group of 20–40 years, who were newly diagnosed and untreated. Thirty age- and body mass index-matched healthy individuals were taken as controls. Clinical and biochemical parameters and ECG were studied. Statistical software, “GraphPad QuickCalcs,” was used for the statistical analysis.

Results: Mean QTc interval of the study group was significantly longer than those of the control group (P = 0.037). Other parameters of ECG were comparable in both the groups.

Conclusion: ECG changes in SCH showed increase in the QTc interval as compared to controls, which predisposes to the potentially life-threatening ventricular arrhythmias. However, the other parameters of ECG such as QRS interval, PR interval, and QRS axis were similar to the controls.

Key words: Subclinical Hypothyroidism; Thyroid Hormones; Electrocardiogram; QTc Interval