Effects of thyroid replacement therapy on arterial blood pressure in patients with hypertension and hypothyroidism.

Background: Hypothyroidism is frequently accompanied by cardiac dysfunction, increased vascular resistance, and a greater prevalence of hypertension. Treatment of hypothyroidism may lead to normalization of blood pressure, although some patients may exhibit sustained hypertension. The mechanism of this condition may be the alterations in aortic stiffness.

Methods: Aortic stiffness was studied in 30 patients who never received treatment for hypertension or hypothyroidism, 15 patients with normal blood pressure and hypothyroidism, and 15 patients with hypertension and normal thyroid function. Thirty healthy age- and sex-matched subjects with normal thyroid function served as control subjects. Aortic diameter evaluated by M-mode echocardiography and blood pressure measured by a sphygmomanometer were used to calculate aortic stiffness index.

Results: Patients with high blood pressure and hypothyroidism, those with normal blood pressure and hypothyroidism, and those with hypertension and normal thyroid function showed increased aortic stiffness index (18.8 +/- 6.4, 11.7 +/- 3.5, and 19.2 +/- 5.3 vs 9.5 +/- 2.7; P <.001) compared with control subjects. In 15 patients with hypertension and hypothyroidism, levothyroxine therapy showed only a small decrease in blood pressure (151/105 +/- 9/9 mm Hg, group A). The remaining 15 patients showed complete normalization of blood pressure (118/83 +/- 8/3 mm Hg, group B). Aortic stiffness index was increased in group A compared with group B both before and after treatment (before, 24.0 +/- 4.1 vs 13.7 +/- 3.2; and after, 22.3 +/- 4.2 vs 11.1 +/- 2.9; P <.001 for both comparisons). Felodipine was given to patients in group A after levothyroxine was administered, resulting in normalization of blood pressure and a significant decrease of aortic stiffness index (P <.001). Aortic stiffness index was decreased in patients with hypothyroidism and hypertension after administration of levothyroxine (9.5 +/- 2.2; P <.001) and felodipine (14.5 +/- 7.5; P <.001) therapy, respectively. Percent changes in systolic blood pressure showed a significant correlation with percent changes in aortic stiffness index in all patients (r = 0.65, P <.001). After multivariate adjustment, aortic stiffness index (odds ratio = 1.9932; confidence interval = 1.1481 to 3.4605) was significantly associated with incomplete normalization of blood pressure.

Conclusions: Patients with hypertension and hypothyroidism have increased aortic stiffness. Aortic stiffness is decreased in all patients, whereas hypertension is completely reversible in 50% of patients by hormone replacement therapy. Sustained hypertension may be due to increased aortic stiffness.