Elevated Levels of Thyroid Hormone Associated With Sudden Cardiac Death

Highlights

• A study conducted in Netherlands looks at the association between thyroid hormone levels and sudden cardiac death.
• 261 sudden cardiac deaths were analyzed.
• Thyroid hormone level was found to increase the risk of sudden cardiac death by 2.5 times.
• The risk levels remained high even after controlling for other risk factors for cardiac death like high blood pressure (hypertension) and high cholesterol.

A sudden cardiac death due to loss of cardiac function was found to be significantly more in people with high levels of thyroid hormone than in people with lower levels. Sudden cardiac death is the cause of more than half of cardiovascular disease associated death and it occurs when there is a malfunction in the heart’s electrical rhythm. Senior author of the study Dr. Layal Chaker from the Netherland’s Erasmus University Medical Center Rotterdam says "Currently, we do not have a good way to predict sudden cardiac death in the general population. Thus identifying additional risk factors is crucial. Our results indicate that thyroid hormone levels may be useful for assessing risk to prevent sudden cardiac death."

Thyroid Hormone

The thyroid hormone is secreted by the thyroid gland that is present at the base of the throat and it is important for the proper functioning of every organ system in the body including the heart and the brain. When the thyroid hormone makes very little hormone, it is called hypothyroidism.

Effects of the Thyroid Hormone on the Heart

The thyroid hormone is known to exert an influence on the functioning of the heart by

• Affecting the force and the rate at which the heart pumps blood.
• Cholesterol level
• Blood pressure

As these crucial parameters are influenced by the thyroid hormone, a problem with the level of thyroid hormone can lead to the development of heart disease or it could make an existing heart condition worse.

Hypothyroidism and the Heart

Hypothyroidism is a condition in which there is lower production of the thyroid hormone. It can lead to the following effects on the heart

• Lowered heart rate
• The artery walls become less elastic
• Increase in blood pressure
• A build up of cholesterol

Hyperthyroidism

Hyperthyroidism is a condition in which there is excess secretion of thyroid hormone in the blood. This condition is very rare and is found to affect only 1% of the population.

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Hyperthyroidism can lead to the following symptoms

• The heart beat is faster
• May lead to abnormal heart rhythms
• Can lead to atrial fibrillation
• Palpitations

Though the connection between the thyroid hormone and the heart have been established before by numerous studies, this study by Dr Layal Chaker and colleagues finds a connection between irregular secretion of the thyroid hormone and sudden cardiac death.

Rotterdam Study

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The Rotterdam study involved a long term finding that delved into the reasons behind heart and other chronic diseases among the elderly people living in the Netherlands. The average age of people who undertook the study was 65 years and they were mostly Caucasians. Women constituted more than half of the study population.

Study that Links Thyroid Hormone and Cardiac Death

Dr Layal Chaker and colleagues studied 10,318 patients who were part of the Rotterdam Study. The death certificates and medical records of patients who died due to sudden cardiac death were analyzed and the level of free thyroxine thyroid hormone levels and the thyroid stimulating hormone in the blood samples.

Results of the Study

The researchers found that 261 study participants died of sudden cardiac death, stressing the prevalence of this condition.

• It was found that free thyroxine hormone levels in the blood that was at the higher end of the normal range was 2.5 times more likely to lead to sudden cardiac death than levels of the hormone at the lower end of the normal range.
• Higher levels of free thyroxine hormone lead to 4 times increase in 10 year risk for sudden cardiac death when compared to low levels of the hormone.
• The high risk for sudden cardiac death due to high thyroxine hormone remained the same even after controlling for other factors like high blood pressure and high cholesterol.

The study shows that elevated levels of thyroxine hormone could increase the risk of sudden cardiac death, which makes it imperative to test for levels of the thyroid hormone in the blood. It is important to understand the risk factors for abnormal thyroid hormone levels and they include:

• Hereditary Factors: The condition could run in the family with people who are first relatives with an affected individual at a higher risk for the disease.
• Age is another important factor, as the age advances, the risk of thyroid problem also increases.
• Gender: It has been found that women are far more likely to be affected by a thyroid problem than men.
• Medical Conditions: There are certain medical conditions which can trigger a thyroid hormone problem like type 1 diabetes, pernicious anemia and Addison’s disease.

It is important to treat high levels of thyroid hormone in the blood to control the risk of sudden cardiac death. The study also raises awareness about the risk associated with hormone replacement therapy as detailed by Dr. Layal Chaker "We know that a considerable proportion of patients on thyroid hormone replacement therapy are over-treated and so have high blood levels of thyroid hormone. Our study suggests more caution is warranted in the treatment of thyroid hormone replacement. Replacement therapy is often aimed at the high normal range which carries a risk of overtreatment."

The study provides a connection between elevated thyroid hormone levels and sudden cardiac death but the researchers highlight that further research may be required to understand if other factors were involved. The thyroid hormone levels were tested at a particular point in the study and this level could have increased or decreased after the testing.

Sudden cardiac deaths display very few symptoms prior to the event and this study offers an insight into a possible mechanism that could lead to it, providing scope for better treatment.

References:

1. Hypothyroidism and Heart Disease - (http://www.hormone.org/questions-and-answers/2013/hypothyroidism-and-heart-disease)
2. Thyroid Disease and Heart - (http://circ.ahajournals.org/content/116/15/1725)
3. Thyroid Hormone: How it affects your heart? - (http://www.health.harvard.edu/heart-health/thyroid-hormone-how-it-affects-your-heart)

Source-Medindia