Increased Central Arterial Stiffness in Hypothyroidism

Hypothyroidism is associated with cardiovascular dysfunction. It is increasingly apparent that stiffening of central arteries may lead to increased afterload and cardiac dysfunction. We noninvasively studied the peripheral and central pressure waveforms in 12 untreated hypothyroid patients as well as in 12 age-, sex-, and body mass index-matched controls using the technique of pulse wave analysis from recordings at the radial artery. Indexes of arterial stiffness, augmentation index (AI) and augmentation of central arterial pressure (AG), were derived as well as time of travel of the reflected wave (TR), a direct estimate of aortic pulse wave velocity. At baseline, there were no significant differences between the 2 groups in brachial and aortic blood pressures. Hypothyroid patients had significantly higher AI than controls (mean +/- SEM[SCAP], 32.0 +/- 3.4% vs. 17.0 +/- 2.4%; P < 0.0005) even when corrected for heart rate (AI(C); 28.0 +/- 3.2% vs. 17.0 +/- 2.4%; P < 0.006) and AG (13.0 +/- 2.2 vs. 7.0 +/- 2.1 mm Hg; P < 0.03) together with a lower TR (132.0 +/- 4.1 vs. 142.0 +/- 1.5 msec; P < 0.03). After 6 months of therapy with T(4), all patients were euthyroid. AI(C) had decreased in the patient group (23.0 +/- 3.2% vs. 28.0 +/- 3.2%; P < 0.01) as had AG (9.0 +/- 1.5 vs. 13.0 +/- 2.2 mm Hg; P < 0.008), but TR was significantly higher (142.0 +/- 3.0 vs. 132.0 +/- 4.1 msec; P < 0.008). AI correlated with age in all groups (hypothyroid group: r = 0.937; P < 0.0005; control group: r = 0.804; P < 0.0005), but correlated with TSH level only among controls (r = 0.591; P < 0.05). This study confirms that hypothyroidism is associated with increased cardiovascular risk, as evidenced by increased augmentation of central aortic pressures and central arterial stiffness. Furthermore, these abnormalities are reversed after adequate T(4) replacement.