Background: Coronary heart disease (CHD) and heart failure (HF) are the leading causes of mortality and morbidity, particularly with the current context of an aging population. Subclinical hypothyroidism (SHypo), defined as elevated serum TSH levels with normal thyroxine values, is common in older adults (5-10%). Prospective cohort studies, as well as analyses of pooled individual participant data suggest up to a 60-90% increase in the risk of CHD or HF events among adults with severe SHypo. However, no large randomized controlled trials (RCT) have assessed the impact of thyroid replacement on cardiovascular (CV) imaging outcomes (largest trial to date: 45 participants). Imaging endpoints are especially well-suited for early trials with investigational therapies for HF treatment and prevention, as well as validated and strong surrogate markers of clinical outcomes.~Specific Aims: The goals of this proposal are to address the impact of thyroid replacement on 1) cardiac function as measured by echocardiography.~Methods: The investigators will conduct a RCT in 185 patients with subclinical hypothyroidism who will be randomly assigned to thyroxine or placebo with an average follow-up of 24 months from baseline (4 death and 17 withdrawal). The main outcome will be CV imaging modalities measured by echocardiography at the close-out visit. Transthoracic echocardiography will be performed for the assessment of diastolic function (abnormalities of the pulsed wave mitral valve inflow pattern and mitral annulus tissue velocities, left atrial volume index, left ventricular [LV] mass index) and cardiac systolic function (LV ejection fraction and regional function). Ultrasound of carotid intima media thickness (CIMT) will be used to assess subclinical atherosclerosis and plaque burden. All images will be centralized at the core lab for a blinded and standardized interpretation.~Expected value of the proposed project: Controversies persist regarding the indications for screening and treatment of SHypo due to the lack of an appropriately powered RCT addressing the impact of thyroid replacement on CV outcomes. Assessment of the impact of thyroid replacement on cardiac function and subclinical atherosclerosis within a trial will aid decisions and evidence-based guidelines development to treat a potential modifiable risk factor, such as SHypo. The strengths of this study include the combination of: 1) High feasibility of the project in collaboration with the largest RCT on SHypo making it possible to investigate the mechanisms of associations with CV disease; 2) Innovative project with combined CV imaging to assess cardiac function with thyroid replacement therapy vs. placebo; 3) Excellent power given the large sample size and participants' older age. The sample size for this proposal will be 5-fold higher than previous small trials of thyroid replacement on CV outcomes. The collaboration of CV imaging modalities expertise with the ongoing largest trial on SHypo, is a unique opportunity to address the clinical and scientific issue of the impact of SHypo on the CV system.
Coronary heart disease (CHD) and heart failure (HF) are the leading causes of mortality and morbidity, particularly with the current context of an aging population. Prospective cohort studies, as well as analyses of pooled individual participant data suggest up to a 60-90% increase in the risk of CHD or HF events among adults with severe SHypo. However, no large randomized controlled trials (RCT) have assessed the impact of thyroid replacement on cardiovascular (CV) imaging outcomes. The goals of this proposal are to address the impact of thyroid replacement on cardiac function. The investigators will conduct a RCT in 185 patients with subclinical hypothyroidism who will be randomly assigned to thyroxine or placebo with an average follow-up of 24 months from baseline. The main outcome will be CV imaging modalities measured by echocardiography at the close-out visit. Assessment of the impact of thyroid replacement on cardiac function and subclinical atherosclerosis within a trial will aid decisions and evidence-based guidelines development to treat a potential modifiable risk factor, such as SHypo.