February is American Heart Month, and unfortunately, most of us know someone who has had heart disease or stroke and this month we will discuss how your thyroid health affects your heart health as well.
The thyroid, a small gland located in the neck, is responsible for modulating many vital bodily functions. By producing just the right amount of thyroid hormone, it helps to regulate the body's metabolism (specifically, how much oxygen and energy the body uses), as well as digestive function, muscle function, and the normal integrity of the skin. In fact, the thyroid has at least some effect on every organ in the body - including the heart.
For people with almost any type of heart disease, disorders of the thyroid gland can worsen old cardiac symptoms or cause new ones, and can accelerate the underlying heart problem. Even worse, doctors frequently forget to think about the thyroid when cardiac symptoms are worsening, and if they don't think of it they will miss it. Often, it's the savvy patient who reminds the doctor that thyroid function ought to be checked. This is why it is useful for those with heart disease to know a little about the cardiac effects of thyroid disease.
Disorders of the thyroid gland usually involve either the failure to produce enough thyroid hormone (hypothyroidism) or the production of too much (hyperthyroidism). Both types of thyroid disorders are common.
Hypothyroidism and the heart
Thyroid hormone is very important for normal cardiovascular function, so when not enough thyroid hormone is present neither the heart nor the blood vessels function normally. In hypothyroidism the heart muscle is weakened in both its contraction phase, and also its relaxation phase. This means that the heart cannot pump as vigorously as it should, and the amount of blood it ejects with each heart beat is reduced. In addition, because the heart muscle does not relax normally in between heart beats, a potentially serious condition called diastolic dysfunction may result. (Read about diastolic dysfunction here). Furthermore, hypothyroidism reduces the amount of nitric oxide in the lining of the blood vessels, causing them to stiffen.
Cardiac symptoms of hypothyroidism
Cardiac symptoms can be seen in anybody with hypothyroidism, but are especially likely in an individual who already has underlying heart disease. Common symptoms include:
· Shortness of breath on exertion and poor exercise tolerance. These symptoms, in most patients with hypothyroidism, are due to weakness in the skeletal muscles; but in patients with heart disease, the symptoms may be due to worsening heart failure.
· Slow heart rate (bradycardia.) The heart rate is modulated by thyroid hormone, so that in hypothyroidism the heart rate is typically 10 - 20 beats per minute slower than normal. Especially in patients who also have heart disease, however, hypothyroidism may worsen the tendency for premature beats and even tachycardias such as atrial fibrillation.
· Diastolic hypertension. One might think that, because a lack of thyroid hormone slows down the metabolism, people with hypothyroidism might suffer from 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 the 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.) Swelling 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. While the reduction in thyroid hormone can actually make angina less frequent in patients who have angina, the increase in LDL cholesterol (bad cholesterol) and in C-reactive protein seen with hypothyroidism can accelerate any underlying coronary artery disease.
Hypothyroidism can be an extremely subtle condition, and often occurs without the typical, constellation of "textbook" symptoms doctors usually expect. It also occurs far more commonly than most doctors realize. So if you have any of these symptoms and your doctor does not have a ready or convincing explanation for them, especially if you already have heart disease of any type, ask your doctor to measure thyroid hormone levels.