The implication of subclinical thyroid disorders on cardiovascular system

Abstract EN

Background: Subclinical hypothyroidism causes changes in cardiovascular function similar to but less marked than those occurring in patients with overt hypothyroidism.

Mild thyroid gland failure evidenced solely by elevation of the serum TSH concentration may be associated with increased morbidity from cardiovascular disorders.

Subclinical hyperthyroidism in which serum TSH levels are decreased in face of normal free thyroid hormones levels in asymptomatic individuals may be also associated with abnormalities in cardiac structure and function.

Objective: The aim of the present study is to clarify the importance of cardio-vascular abnormalities mainly atherosclerosis in subclinical dysthyroidism in order to define the best way of treatment and follow up.

Study Design: Sixty subjects, selected from the endocrine clinic, Ain Shams University Hospital, 59 females and 1 male with mean age 31.6 + 8.4 years.

They were divided into twenty patients with subclinical hypothyroidism (Group A), twenty patients with subclinical hyperthyroidism (Group B), and twenty healthy subjects as control group (Group C).

All subjects were subjected to full history taking, thorough clinical examination, thyroid function tests, thyroid antibody assessment, thyroid Ultra Sound, Color Doppler Scan of the thyroid, Technetium 99m thyroid Scan, Carotid arterial duplex sonography, Electrocardiogram, Holter ECG and Echocardiographic study. Results: Subclinical hypothyroid patients showed a significant increase in serum total cholesterol, LDL-C and TG while HDL-C was not affected compared to the control, - Significant negative variation in pulse rate but without any significant difference in both systolic and diastolic function. - Non significant increase in left ventricular mass compared to the control.

As regard subclinical hyperthyroid patients they showed no statistically significant difference regarding all lipid profile (S.

chole-TG, LDL-C and HDL-C). - Significant increase in heart rate but did not show any significant prevalence of atrial fibrillation or atrial premature contractions.

No significant alteration in both systolic and diastolic functions. Conclusion: Subclinical hypothyroidism is associated with altered pulse rate and dyslipidemia which enhace cardiovascular risk disease.

Subclinical hyperthyroidism was only associated with increased pulse rate.

These present observations do not support the need for treatment of subclinical hyperthyroidism except in elderly patients with increasing risk of developing cardiac arrhythmias.

However, the treatment of endogenous subclinical hyperthyroidism in young and middle-aged patients is controversial.