Subclinical Hypothyroidism Not Associated With Higher Mortality Rates in Older Patients Post Angioplasty

New research shows that elderly patients with subclinical hypothyroidism undergoing coronary angioplasty may have no greater risk of death after the procedure in the long-term than their younger counterparts.

Published in the March 5 in BMC Endocrine Disorders, Chinese researchers led by Ming-Qi Zheng, PhD, of the First Hospital of Hebei Medical University, sought to determine the mortality rate at four years post-op for elderly patients with subclinical hypothyroidism who undergo percutaneous coronary intervention, or coronary angioplasty.

Subclinical hypothyroidism is usually asymptomatic in the elderly affecting about 10% of the general population. In these patients, thyroid hormone levels are normal, while thyroid-stimulating hormone (TSH) levels are generally above normal. It is well established that patients with subclinical hypothyroidism have an increased risk for developing cardiovascular disease. The condition is associated with worsening blood pressure, atherogenic dyslipidemia, impaired cardiac contractile and diastolic function, increased systemic vascular resistance, endothelial dysfunction, accelerated atherosclerosis, enhanced inflammation level, hypercoagulability, insulin resistance and oxidative stress.  

“Our results suggest that subclinical hypothyroidism may not an independent risk factor for mortality in older patients undergoing percutaneous coronary intervention (PCI). The increase of serum TSH observed in the elderly may represent a physiological process reflecting a certain degree down-regulation hypothalamus-pituitary-thyroid-peripheral (HPTP) axis. Therefore, subclinical hypothyroidism, especially mild elevation of TSH, should not be regarded as a pathological condition in older patients undergoing PCI,” Zheng et al. wrote.

Dr. Zheng and colleagues conducted a retrospective cohort study of 3,168 patients 65 years old or older, who underwent coronary angioplasty between January 2012 to October 2014. Patients were screened for subclinical hypothyroidism before the procedure with thyroid function testing—which included thyroid stimulating hormone (TSH), total triiodothyronine (TT3), total thyroxine (TT4), free triiodothyronine (FT3) and free thyroxine (FT4). Of 3,168 patients, 320 (10.1%) had subclinical hypothyroidism and 2,848 (89.9%) had normally functioning thyroid glands.

By four years post-op, there were 227 deaths (29 with subclinical hypothyroidism and 198 with normally functioning thyroid) of which 124 were due to cardiac events (16 deaths in the subclinical hypothyroidis group and 108 in the euthyroid group). Researchers found no significant difference in mortality rates between patients with subclinical hypothyroidism or group with normal functioning thyroid glands (P > 0.05).

The relative risk of death from all-cause and cardiac in patients with subclinical hypothyroidism were 1.261 (95% CI: 0.802–1.982, P = 0.315) and 1.231 (95% CI: 0.650–2.334, P = 0.524), respectively. No significant associations with mortality were found after factoring in age, gender, and degree of thyroid-stimulating hormone elevation.

The 4-year cumulative all-cause mortality rates in patients with subclinical hypothyroidism and euthyroid were 9.1% and 7.0%, respectively. The 4-year cumulative cardiac mortality rates were 5.0% and 3.8%, respectively. The Kaplan-Meier analysis showed no significant difference in all-cause mortality and cardiac mortality between the two groups.

The authors noted their findings differ from those published by Alon Grossman, MD, et al. in 2015 in the American Journal of Medicine in which Grossman et al. found that subclinical hypothyroidism was associated with an increased risk for mortality in elderly patients.

Other limitations of the Zheng et al. study included that it was a single-center retrospective study; the thyroid function test was only taken once at baseline; and, the study did not include patients with existing acute cardiac disease.

“Owing to the relatively few studies [on this subject], the result should be interpreted carefully and confirmed by further studies. To date, most of the findings in the elderly were derived from the general population. Although subclinical hypothyroidism has been associated with an increased risk of mortality in patients with established cardiovascular disease, it is ambiguously defined whether SCH increases the risk of mortality in older patients with established cardiovascular disease,” Zheng et al. wrote.

Disclosures:  The authors declared no conflicts of interest.

References

1. Yong-Sheng Liu, Mei Wei, Le Wang, Gang Liu, Guo-Ping Ma, Katsushige Ono, Ze-Long Cao, Man Yang & Ming-Qi Zheng. “The impact of subclinical hypothyroidism on long-term outcomes in older patients undergoing percutaneous coronary intervention,” BMC Endocrine Disorders. March 5, 2021. 21, 43 (2021). https://doi.org/10.1186/s12902-021-00702-z
2. Grossman A, Weiss A, Koren-Morag N, Shimon I, Beloosesky Y, Meyerovitch J. “Subclinical thyroid disease and mortality in the elderly: a retrospective cohort study.” American Journal of Medicine. 2016;129:423–30.