Thyroid and heart function
Disease of the thyroid gland often produces heart problems. One of the most important reasons to diagnose and treat thyroid disease is to prevent the cardiac conditions that can result from it. Thyroid disease affects the heart either by producing too little thyroid hormone (a condition called hypothyroidism) or too much thyroid hormone (called hyperthyroidism). Both types of thyroid disorders are common and both can have a significant effect on the heart.
Thyroid hormone has direct effects on heart function, blood vessels and cholesterol levels. Thyroid hormone influences the force and speed of your heartbeat, your blood pressure, and your cholesterol level. As a result, a malfunctioning thyroid gland can cause problems that masquerade as heart disease or make existing heart disease worse.
Hypothyroidism: The cardiac connection
For people with almost any type of heart disease, disorders of the thyroid gland can worsen old cardiac symptoms or contribute to new ones. New research now strengthens the evidence that thyroid disorders and heart disease may also be a deadly combination.
In hypothyroidism, symptoms may include slowing of the heart rate, constriction of the blood vessels and increased blood pressure, retention of fluid and edema and an increase in cholesterol levels. Severe cases of hypothyroidism can cause heart failure and death. Hypothyroidism is treated with thyroid hormone replacement, which can reverse most of these negative effects. However, overtreatment of hypothyroidism can result in high thyroid levels and fast and irregular heart rates.
In hypothyroidism, the reduced level of thyroid hormone causes the heart muscle to pump less vigorously and eventually to become weakened. In addition, the heart muscle cannot fully relax after each heartbeat. This failure to relax can produce diastolic dysfunction, a condition that can lead to heart failure. Hypothyroidism also causes blood vessels to stiffen, which can produce hypertension.
Hypothyroidism can affect the heart and circulatory system in a number of ways. Insufficient thyroid hormone slows your heart rate. Because it also makes the arteries less elastic, blood pressure rises in order to circulate blood around the body. Elevated cholesterol levels, which contribute to narrowed, hardened arteries, are another possible consequence of low thyroid levels.
Another noncardiac symptom—muscle aches—may also be relevant. Muscle aches can be a symptom of hypothyroidism as well as a side effect of cholesterol-lowering statin medications, a condition known as statin-related myalgia.
Common signs and problems of heart disease in people with hypothyroidism
Cardiac symptoms can occur in anybody with hypothyroidism, but they are especially likely in people who already have underlying heart disease. Common cardiac problems associated with hypothyroidism include:
Dyspnea: Shortness of breath on exertion and poor exercise tolerance in hypothyroidism is usually due to weakness in the skeletal muscles. In people who also have heart disease, it may be due to worsening heart failure.
Slow heart rate (bradycardia): The heart rate is modulated by thyroid hormone. So, with hypothyroidism, the heart rate is typically 10 to 20 beats per minute slower than normal. Especially in patients who also have heart disease, however, hypothyroidism may worsen the tendency for premature beats (such as PVCs ) and may cause atrial fibrillation.A slower heart rate leads to less blood pumped to the rest of the body.
Diastolic hypertension: One might think that, because a lack of thyroid hormone slows down the metabolism, people with hypothyroidism might experience low blood pressure. Usually, the opposite is true—the arteries are stiffer in hypothyroidism, which causes the diastolic blood pressure to rise.
Worsening of heart failure or new onset of heart failure: Hypothyroidism can make well-controlled heart failure worsen and can produce heart failure for the first time in patients with relatively mild underlying heart disease.
Edema (swelling): Edema can occur as a result of worsening heart failure. In addition, hypothyroidism itself can produce a type of edema called myxedema, caused by an accumulation of abnormal proteins and other molecules in the interstitial fluid (fluid external to the body’s cells).
Worsening of coronary artery disease (CAD): While the reduction in thyroid hormone can actually make angina (chest discomfort associated with CAD) less frequent in patients who have angina, the increase in LDL cholesterol (bad cholesterol) and in C-reactive protein seen with hypothyroidism may accelerate any underlying CAD.
References
https://www.health.harvard.edu/heart-health/thyroid-hormone-how-it-affects-your-heart
https://endocrinenews.endocrine.org/hypothyroidism-and-the-heart/
https://www.verywellhealth.com/thyroid-disease-and-the-heart-1746112
