Endothelial-mediated coronary flow reserve in patients with mild thyroid hormone deficiency

Although coronary flow reserve (CFR) is reduced in patients with subclinical hypothyroidism (SHypo), the endothelial response of coronary vasomotion has never been explored in this clinical setting.

To investigate the endothelial response of coronary flow in young and middle-aged patients with SHypo, without associated cardiovascular risk factors compared with healthy control subjects.

The study population consisted of 20 women (mean age 38.4+12.1 years) with newly diagnosed, untreated and persistent SHypo due to Hashimoto's thyroiditis. A total of 15 volunteers served as controls. Age, gender, body surface area, glucose, insulin levels, heart rate, systolic, diastolic, and mean blood pressure were similar in patients and controls. Body mass index was significantly higher in SHypo patients. Total cholesterol and low-density lipoprotein cholesterol, despite not significant, tended to be higher, and high-density lipoprotein cholesterol to be lower in SHypo. Coronary blood flow velocities were recorded in patients at rest and after the cold pressor test (CPT), a stimulus that can be considered totally endothelium-dependent. CFR was calculated as the ratio of hyperemic-to-resting diastolic peak velocities.

Coronary diastolic peak velocities at rest did not differ between the two groups but were significantly lower after CPT in patients with SHypo, thereby resulting in a lower CFR. The difference remained significant after adjusting resting and CPT velocities for the respective mean blood pressures. TSH was inversely correlated with CFR in the pooled population.

Patients with SHypo without associated cardiovascular risk factors have a coronary endothelial dysfunction that appears in response to a physiological stimulus (the CPT).