ReviewArterial hypertension and thyroid disorders: What is important to know in clinical practice?Hypertension artérielle et pathologie thyroïdienne : points importants en pratique clinique
Introduction
Variations from the euthyroid status affect virtually all physiological systems but the effects on BP regulation are particularly pronounced [1], [2]. At population level, the relationship between thyroid hormones and the different BP components is not well established. Asvold et al. [3] reported a linear correlation between TSH and both systolic and diastolic BP, whereas other authors did not find this association [4], [5], [6]. Conversely, in clinical practice, it is well known that the effects of hyperthyroidism on clinic BP are opposite to those occurring in hypothyroidism [7]. HT is frequently observed both in hyper- and hypothyroidism, suggesting that different mechanisms are involved in thse two conditions [2], [8]. However, several studies have shown that hyperthyroidism accelerates [9] while hypothyroidism prevents and reverses some models of experimental HT [10] and that HT related to hypothyroidism is reversible after T4 treatment [11]. However, in some cases, a pharmacological treatment with anti-hypertensive drugs to control BP is required.
Section snippets
Thyroid hormone effects on blood pressure regulation
BP is the result of the following algorithm: CO × SVR. As a consequence, the effect of thyroid hormones on BP regulation derives particularly from their interaction with these two parameters [12]. However, thyroid hormones influence other hemodynamic items such as HR, cardiac contractility and blood volume (Table 1).
CO is strongly regulated by HR, and because it determines the rate of cardiac ejection, it affects both systolic and diastolic ventricular function [7]. In addition, the effect of HR
Hyperthyroidism and blood pressure
The prevalence of HT is nearly three-fold higher in patients with overt hyperthyroidism than in normal subjects. Overt hyperthyroidism and thyrotoxicosis are associated with high BP levels [15]. It is estimated that the prevalence of HT with thyrotoxicosis ranges between 20 to 30%, but there are limited studies to confirm these data because HT is a highly frequent condition [2].
T3, the active form of thyroid hormones, dilates resistance arterioles [16] and reduces SVR [17] by the direct
Subclinical hyperthyroidism
Endogenous SH, defined by normal circulating levels of free T4 (FT4) and T3 (FT3) and low levels of TSH, is a common clinical entity and is typically caused by the same conditions that cause overt hyperthyroidism [34]. The diagnosis of SH derives from laboratory and not from clinical signs. SH is characterized by a low or undetectable concentration of serum TSH with both FT3 and FT4 levels within laboratory reference ranges. The cardiovascular risk of SH is related to short-term effects
Hypothyroidism and blood pressure
After renovascular HT, hypothyroidism is recognised as the second more important form of secondary HT, but it is often ignored or overlooked. In hypothyroid subjects from the general population, the prevalence of HT varies widely from 1 to 50% [4], [5], [6], [36]. This is due to the different criteria used to define both hypothyroidism and HT, and on the age of the subjects analysed [37], [38]. Like other forms of secondary HT, hypothyroidism increases with age and its prevalence is higher in
Subclinical hypothyroidism
The role of SCH in cardiovascular disorders is a matter of debate and controversy, in particular as concerning its relationship with HT. In the past few years, several population-based studies have been investigating the association of SCH with BP and HT [4], [5], [34]. In one of these studies, subjects with SCH had a 2.8-fold increased risk of HT compared to euthyroid subjects [36]. Other studies however, did not found any association [4], [5]. The prevalence of SCH range from 5 to 15% of the
Anti-hypertensive treatment in thyroid disorders
HT secondary to thyroid dysfunctions is usually reversible with the achievement of euthyroidism [65]. This finding would encourage the routine assessment of thyroid function in all patients with pre-existing HT that becomes resistant to pharmacological treatment. However hypertension may not resolve immediately when normalization of serum T4, and moderate to severe HT should be treated also with antihypertensive drugs (Table 3).
The treatment of isolated systolic BP in hyperthyroidism should be
Disclosure of interest
The authors declare that they have no conflicts of interest concerning this article.
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