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Subclinical Hypothyroidism, Arterial Stiffness, and Myocardial Reserve

Centre for Endocrine and Diabetes Sciences (P.J.D.O., J.H.L.) and Department of Cardiology (C.R., D.V., T.M., A.G.F.), School of Medicine, Cardiff University, Cardiff CF14 4XN, Wales, United Kingdom

Address all correspondence and requests for reprints to: Professor J. H. Lazarus, Centre for Endocrine and Diabetes Sciences, Cardiff University, University Hospital of Wales, Cardiff CF14 4XN, Wales, United Kingdom. E-mail: lazarus{at}cf.ac.uk.

Context: Subclinical hypothyroidism (SCH) is associated with increased risk of cardiac disease; its impact on arterial function is less clear.

Objective: The objective of the study was the assessment of arterial and cardiac function.

Design: The study was a 6-month controlled observational study using pulse wave analysis and tissue Doppler dobutamine stress echocardiography.

Setting: The study was conducted at a thyroid clinic.

Patients: Nineteen female SCH patients with raised TSH, normal free T₄, and no cardiovascular disease [aged 49.2 ± 3.8 yr; body mass index (BMI) 29.9 ± 6.7 kg/m²] were recruited from the thyroid clinic, and 10 female controls (aged 50.2 ± 3.4 yr; BMI 29.7 ± 7.2 kg/m²) also participated in the study.

Interventions: Incremental doses of L-thyroxine were used.

Main Outcome Measures: Indices of vascular stiffness and left ventricular echocardiographic function were measured.

Results: Baseline augmentation gradient was elevated in SCH, compared with controls [10.3 ± 5.1 (SD) mm Hg vs. 8.0 ± 4.2, P < 0.05]; when euthyroid (mean T₄ dose 114 µg/d), it fell to 8.8 ± 5.3 mm Hg (P < 0.05). Heart rate-corrected augmentation index was 26.7 ± 9.9 vs. 18.8 ± 9.9% (P < 0.02), falling to 19.7 ± 9.6% (P < 0.001) after treatment. Time of travel of the reflected wave was 139.3 ± 11.7 msec, compared with 141.5 ± 8.8 msec in controls (P < 0.05), increasing to 144.9 ± 11.9 msec (P < 0.05). There were no differences in resting global, regional left ventricular function, or regional myocardial velocities during maximal dobutamine stress between SCH patients and controls, or in treated patients, compared with baseline.

Conclusions: Arterial stiffness was increased in SCH and improved with L-thyroxine, which may be beneficial, whereas myocardial functional reserve was similar to controls and remained unaltered after treatment.

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