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Published on: December 13, 2019
The association between TSH and thyroid hormones in the normal or subclinical dysfunction range with left ventricular
Ji Eun Jun1, Tae Hyuk Kim2, Sun Wook Kim3
1Department of Endocrinology and Metabolism, Kyung Hee University Hospital at Gangdong, Kyung Hee University College of Medicine, Seoul, Republic of Korea.
Insights
Subclinical hypothyroidism, but not subclinical thyrotoxicosis, is linked to left ventricular diastolic dysfunction. Thyroid hormone T3 levels within the normal range also impact diastolic function, highlighting thyroid status
Area of Science:
- Cardiology
- Endocrinology
- Thyroidology
Background:
- Thyroid hormones significantly influence cardiovascular function.
- The precise impact of subclinical thyroid dysfunction and euthyroid thyroid hormone levels on cardiac function remains incompletely understood.
- Left ventricular (LV) diastolic dysfunction is a critical indicator of cardiac health.
Purpose of the Study:
- To investigate the association between subclinical thyroid dysfunction and LV diastolic dysfunction.
- To explore the relationship between thyroid hormones within the normal reference range and cardiac function.
- To clarify the role of subclinical hypothyroidism and subclinical thyrotoxicosis in diastolic dysfunction.
Main Methods:
- A cross-sectional study involving 26,289 participants from the Republic of Korea.
- Participants were categorized into euthyroid, subclinical hypothyroidism, and subclinical thyrotoxicosis groups based on thyroid-stimulating hormone (TSH), free thyroxine (FT4), and triiodothyronine (T3) levels.
- Cardiac structure and function, specifically LV diastolic dysfunction, were assessed using echocardiography.
Main Results:
- Subclinical hypothyroidism was significantly associated with increased odds of LV diastolic dysfunction (adjusted odds ratio [AOR] 1.36).
- Subclinical thyrotoxicosis did not show a significant association with LV diastolic dysfunction.
- Serum triiodothyronine (T3) levels within the normal range were inversely associated with LV diastolic dysfunction, suggesting a more significant role than TSH or FT4.
Conclusions:
- Subclinical hypothyroidism is a significant risk factor for developing left ventricular diastolic dysfunction.
- Subclinical thyrotoxicosis does not appear to be associated with LV diastolic dysfunction.
- Serum T3 levels, even within the normal range, play a notable role in modulating LV diastolic function.
Abstract:
Thyroid hormones modulate the cardiovascular system. However, the effects of subclinical thyroid dysfunction and euthyroidism on cardiac function remain unclear. We investigated the association between left ventricular (LV) diastolic dysfunction and subclinical thyroid dysfunction or thyroid hormones within the reference range. This cross-sectional study included 26,289 participants (22,197 euthyroid, 3,671 with subclinical hypothyroidism, and 421 with subclinical thyrotoxicosis) who underwent regular health check-ups in the Republic of Korea. Individuals with thyroid stimulating hormone (TSH) levels > 4.2 µIU/mL and normal free thyroxine (FT4, 0.78-1.85 ng/dL) and triiodothyronine (T3, 76-190 ng/dL) levels were defined as having subclinical hypothyroidism. Individuals with serum TSH levels < 0.4 µIU/mL and normal FT4 and T3 levels were defined as having subclinical thyrotoxicosis. The cardiac structure and function were evaluated using echocardiography. LV diastolic dysfunction with normal ejection fraction (EF) was defined as follows: EF of > 50% and (a) E/e' ratio > 15, or (b) E/e' ratio of 8-15 and left atrial volume index ≥ 34 mL/m2. Subclinical hypothyroidism was significantly associated with cardiac indices regarding LV diastolic dysfunction. The odds of having LV diastolic dysfunction was also increased in participants with subclinical hypothyroidism (adjusted odds ratio [AOR] 1.36, 95% confidence interval [CI], 1.01-1.89) compared to euthyroid participants. Subclinical thyrotoxicosis was not associated with LV diastolic dysfunction. Among the thyroid hormones, only serum T3 was significantly and inversely associated with LV diastolic dysfunction even within the normal range. Subclinical hypothyroidism was significantly associated with LV diastolic dysfunction, whereas subclinical thyrotoxicosis was not. Serum T3 is a relatively important contributor to LV diastolic dysfunction compared to TSH or FT4.
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