Impact of resistance to thyroid hormone on the cardiovascular system in adults

The clinical manifestations of resistance to thyroid hormone (RTH) are highly variable, and the impact of RTH on the cardiovascular system has been poorly investigated.

The objective of the study was to evaluate the cardiovascular characteristics of 16 untreated and asymptomatic patients with RTH compared with 16 euthyroid healthy controls to define the cardiovascular involvement in RTH syndrome.

Sixteen untreated and asymptomatic RTH patients (eight males; aged 33 +/- 12 yr, range 21-45 yr) and 16 controls (nine males; aged 33 +/- 5 yr, range 24-42 yr) were enrolled. Clinical data, thyroid status, and echocardiographic results were recorded.

Heart rate was comparable with that of controls, whereas arterial pressure was higher than controls. Mean interventricular septum diastolic thickness and mean left ventricular (LV) posterior wall diastolic thickness were significantly lower in RTH patients than controls with a consequent significant decrease of the mean LV mass and LV mass indexed by body surface area. Patients also had abnormalities of myocardial relaxation as indicated by a significant increase of peak A and consequent reduction of the early to late ratio. Finally, systemic vascular resistance was significantly higher in RTH patients than controls.

Our results suggest the presence of cardiovascular alterations in asymptomatic and untreated RTH patients similar to those reported in hypothyroid patients. Our strict selection likely created a bias in the inclusion of a particular type of RTH patients, who could represent a minority of patients with RTH. However, no correlation was found between the type of mutation and cardiovascular characteristics of RTH patients.