Levothyroxine improves abnormal cardiac bioenergetics in subclinical hypothyroidism: A cardiac magnetic resonance spectroscopic study

Abstract

Context: It is well established that subclinical hypothyroidism (SCH) is associated with mild cardiac dysfunction, but it is unknown whether there is an underlying impairment of cardiac bioenergetic function. Objective: The objective of the study was to quantify the cardiac phosphocreatine to adenosine triphosphate ratio (PCr to ATP) in SCH, compared with healthy controls, and to measure the effect of 6 months of levothyroxine treatment. Design and Setting: This was a 6-month, prospective, case-controlled interventional study. Participants and Main Outcome Measures: The PCr to ATP ratio was measured using phosphorus-31 magnetic resonance spectroscopy in subjects with SCH at baseline and after levothyroxine therapy (1.6μg/kg·d) and compared with age- and gender-matched euthyroid controls. All subjects were free of overt heart disease. Results: Twenty-one subjects with SCH (normal free T4 and serum TSH between 4.1 and 10 mIU/L) and 17 controls were matched for age (mean age 40.5 vs 43.3 y) and sex (females 81% vs 82%) but differed in mean TSH (6.5 vs 2.1 mIU/L, P