Hyperthyroidism...The Heart of the Matter
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.