Hyperthyroidism...The Heart of the Matter

Medical Author: Ruchi Mathur, M.D.
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

I see a number of patients with hyperthyroidism. Very frequently, their symptoms involve the heart. The most common symptoms are a feeling of palpitations and a sensation of a racing heart beat. These symptoms are due to a physiologic effect of thyroid hormone on the heart. I thought I'd take a moment to explain more about what impact thyroid hormone can have on the heart and why these symptoms result.

Many of the signs and symptoms patients experience when they are diagnosed with hyperthyroidism result from the direct effect of thyroid hormones on the heart. While heart effects are also seen in hypothyroidism, they are usually much more obvious in hyperthyroidism.

Excess thyroid hormone causes palpitations and some degree of exercise intolerance that is due to an increased heart rate and fatigue. The changes in heart rate are a result of a change in the nervous system's control on the heart. With excess thyroid hormones in the body, a heart rate of greater than 90 beats per minute (tachycardia) is common, even at rest and when asleep. In addition, the normal increase in heart rate during exercise is exaggerated. A rapid heart rate is one of the most common signs of hyperthyroidism.

The amount of blood pumped out by the heart is also increased in hyperthyroidism. This may be important in patients who have weak hearts, because this increased workload on the heart muscle may result in heart failure.

While a rapid regular heart beat is the most common rhythm variation in hyperthyroidism, an irregular heart rhythm called atrial fibrillation is also common. Atrial fibrillation occurs as a result of the chaotic beating of the smaller, upper chambers of the heart (the atria). Instead of passing the blood to the larger, stronger ventricles in a coordinated fashion to allow for distribution throughout the body, the atria are less effective because their contractions are disorganized. This results in poorer filling of the ventricles and inefficient pumping of blood throughout the body. Atrial fibrillation is seen in 5 to 15% of patients with hyperthyroidism and may often be the problem that induces the patient to see the doctor. When a new case of atrial fibrillation is discovered, doctors will often check a patient's thyroid function to make certain this is not the first symptom of hyperthyroidism, which is a treatable cause of atrial fibrillation.

What does all of this mean?

Well, there are 2 important ways to approach this relationship between thyroid disease and the heart.

  1. If you have been diagnosed with hyperthyroidism and are having a sensation of shortness of breath, palpitations, or chest discomfort, do not assume it's just nerves. Bring it to your doctor's attention immediately. There are simple tests your doctor can perform, such as an EKG and an ultrasound, to assess your heart function.
  2. If you have a new onset of a heart problem, particularly atrial fibrillation, ask your doctor to check your thyroid by performing a simple blood test. The good news is that controlling hyperthyroidism, when present, often results in significant improvement of the heart symptoms.

The most important thing to remember is to tell your doctor if you have any concerns or questions so that the doctor can help you achieve your best health. Together, you can get to the heart of the matter.

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