By producing just the right amount of thyroid hormone, the thyroid helps regulate your body’s metabolism, most importantly the amount of oxygen and energy your body uses, as well as your digestive function, muscle function, and skin tone. In fact, the thyroid has at least some effect on every organ in the body, including the heart.
In a person with almost any type of heart disease, thyroid gland disorders can make heart symptoms worse or cause new ones and can accelerate the underlying heart problem . Thyroid disease can even lead to entirely new heart problems in people with healthy hearts.
Thyroid disease affects the heart by either 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 is very important for normal cardiovascular function. When there is not enough thyroid hormone, neither the heart nor the blood vessels can function normally.
In hypothyroidism , the reduced level of thyroid hormone causes the heart muscle to pump with less force and eventually becomes weak. Also, the heart muscle cannot fully relax after each beat.
This lack of relaxation can lead to diastolic dysfunction, a condition that can lead to heart failure. Hypothyroidism also causes blood vessels to harden, which can lead to hypertension.
Cardiac symptoms can occur in anyone with hypothyroidism, but they are more likely to develop in people who already have underlying heart disease.
Heart problems associated with hypothyroidism
Common heart problems associated with hypothyroidism include:
Shortness of breath on exertion and poor exercise tolerance in hypothyroidism are 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 when there is hypothyroidism, the heart rate is usually 10 to 20 beats per minute slower than normal. However, hypothyroidism can worsen the tendency to premature beats (like PVCs) and can cause atrial fibrillation.
You might think that because a lack of thyroid hormone slows down metabolism, people with hypothyroidism may experience low blood pressure. The reverse is generally true: Your arteries are stiffer when you have hypothyroidism, causing your diastolic blood pressure to rise.
Worsening heart failure or new onset heart failure
Hypothyroidism can worsen controlled heart failure and can lead to heart failure for the first time in patients with relatively mild underlying heart disease.
Edema can occur as a result of worsening heart failure. Also, hypothyroidism itself can lead to a type of edema called myxedema, caused by a build-up of abnormal proteins and other molecules in the interstitial fluid (fluid outside the body’s cells).
Worsening of coronary artery disease (CAD)
Although the reduction in thyroid hormone may actually make angina (chest discomfort associated with CAD) less common in patients with angina, the increase in LDL (bad cholesterol) and C-reactive protein during hypothyroidism can accelerate any underlying CAD.
Hypothyroidism is often an extremely subtle condition. It usually has a very gradual onset, so its symptoms can “creep up” on you. Also, especially in older people, hypothyroidism often occurs without the presence of typical “textbook” symptoms that doctors often expect to appear.
Hypothyroidism is treated with thyroid hormone medications. Proper treatment of hypothyroidism is a bit complicated and even controversial.
Hypothyroidism is more common than many doctors think. If you have any symptoms that suggest hypothyroidism and your doctor doesn’t have an explanation for them (especially if you already have heart disease of any kind), you should ask your doctor to measure your thyroid hormone levels.
The hyperthyroidism is caused by overproduction of thyroid hormone. When there is too much thyroid hormone, the heart muscle “whips” like a horse, and for a person with heart disease, that would be the same as whipping an exhausted horse.
Excess thyroid hormone increases the force of contraction of the heart muscle and increases the amount of oxygen required by the heart. It also increases the heart rate. As a result, the work of the heart increases considerably.
Heart conditions caused by hyperthyroidism
Cardiac symptoms can occur in anyone with hyperthyroidism, but they can be particularly dangerous in people with underlying heart disease. Common symptoms include:
Fast heart rate (tachycardia) and palpitations
Hidden (that is, not apparent) hyperthyroidism is a common cause of an increased heart rate at rest and with mild exertion. Hyperthyroidism should always be ruled out with blood tests before making an inappropriate diagnosis of sinus tachycardia.
Hyperthyroidism, especially in patients with underlying heart disease, can also cause a host of other arrhythmias, including PVC, ventricular tachycardia, and atrial fibrillation . In fact, it’s important to rule out hyperthyroidism in anyone who has atrial fibrillation without a clear underlying cause.
- Systolic hypertension: Strong cardiac contraction increases systolic blood pressure (the pressure within the blood vessels during cardiac contraction).
- Dyspnea on mild exertion: Shortness of breath may be due to skeletal muscle weakness associated with hyperthyroidism or worsening heart failure.
- Heart failure: Hyperthyroidism itself can lead to heart failure, but only rarely. On the other hand, if there is pre-existing heart disease, worsening heart failure with hyperthyroidism is common and can be extremely difficult to treat.
- Worsening angina: CAD patients often experience a worsening of symptoms when hyperthyroidism is present. These can include an increase in angina or even a heart attack.
As with hypothyroidism, hyperthyroidism can be present without producing the classic textbook symptoms. Therefore, anyone who has any of these cardiac symptoms that cannot be explained otherwise should have their thyroid function measured.
The “best” way to treat hyperthyroidism is controversial. In the United States, most doctors immediately opt for ablation of the overactive thyroid gland with radioactive iodine. They then give the patient thyroid hormone pills, as the thyroid gland is no longer working.
However, this can sometimes be counterproductive, as an overactive thyroid is occasionally a transient phase of Hashimoto’s disease , in which case ablation of the thyroid gland is unnecessary.