Impact of Thyroid Dysfunction on the Cardiovascular System in Elderly Patients

CV consequences of hypothyroidism in elderly patients

Manifest hypothyroidism is confirmed by laboratory findings of low concentrations of fT4 and elevated concentrations of TSH (> 4.5 mIU/l). More commonly, we encounter so-called subclinical hypothyroidism, characterized by normal fT4 concentration but already elevated TSH concentration.

Patients with hypothyroidism have, among other risks, a higher risk of dyslipidemia, premature development of atherosclerosis, and myocardial contractility disorders in terms of systolic or diastolic dysfunction.

According to recent studies, TSH values seem to increase with age. An increase of approximately 0.3 mIU/l every 10 years is reported. However, the results are not unequivocal; earlier studies reported unchanged or even decreasing TSH levels in old age. There also remains a question of what impact this trend has on cardiovascular morbidity and mortality.

Results from some studies suggest that in patients with subclinical hypothyroidism, the risk of ischemic heart disease (IHD) and CV mortality is increased only in younger age, not in patients over 65. In one study, the positive effect of levothyroxine as a substitute treatment for subclinical hypothyroidism on reducing the risk of CV events was observed only in patients younger than 70. In the group of patients older than 85, lower CV mortality was even observed in the case of subclinical hypothyroidism compared to patients with normal thyroid function. Additionally, the largest available meta-analysis did not confirm a higher risk of CV mortality in patients with subclinical hypothyroidism, except for a subgroup of patients with TSH > 7 (hazard ratio [HR] 1.42) and > 10 mIU/l (HR 1.58). Subgroup analysis by age was not performed here.

Hyperthyroidism and CV risk

The diagnosis of peripheral hyperthyroidism is established based on high serum concentrations of fT4 and low concentrations of TSH. Similarly, subclinical hyperthyroidism is characterized by normal serum concentrations of thyroid hormones with low TSH concentration.

Hyperthyroidism is generally associated with an increased risk of developing arrhythmias (especially atrial fibrillation) and heart failure, and this holds true across all age groups. It should therefore always be treated regardless of age.

In patients older than 60 years with TSH < 0.1 mIU/l, studies have observed up to a 3-time higher risk of atrial fibrillation than in individuals with normal thyroid function (with a cumulative incidence of 28% over 10 years). The risk of atrial fibrillation was greater the lower the TSH values. Conversely, the impact of hyperthyroidism on increasing the risk of IHD appears to be weaker, and studies do not show consistent results.

Some studies have even demonstrated higher CV mortality (from cardiac as well as cerebrovascular diseases) in patients with hyperthyroidism over 60 years of age.

Discussion and conclusion

It appears that subclinical hypothyroidism is clinically less significant compared to hyperthyroidism with increasing age. This might hypothetically be due to its atherogenic effect being balanced out with a potentially protective effect of overall metabolic slowdown in old age. However, its negative consequences might be masked by other CV risk factors, such as dyslipidemia. Nevertheless, higher threshold values of TSH for initiating substitute treatment for subclinical hypothyroidism in patients over 65 years of age seem justified. Currently, it is recommended to start this treatment at TSH values > 10 mIU/l. A similar approach does not apply to hyperthyroidism, which demonstrably increases CV morbidity (especially the risk of atrial fibrillation) in elderly patients and should always be treated.

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Source: Barbesino G. Thyroid function changes in the elderly and their relationship to cardiovascular health: a mini-review. Gerontology 2019; 65 (1): 1−8, doi: 10.1159/000490911.