Brian A. McGovern
Co-Director, Cardiac Arrhythmia Service, Cardiac Unit
Massachusetts General Hospital
On May 7, 1991, President George Bush noted that his heart suddenly began to beat in a rapid and erratic manner. He was diagnosed with atrial fibrillation, a common heart rhythm disturbance in older individuals with underlying heart problems such as high blood pressure, coronary artery disease, or trouble with one of the heart valves. The President was not known to have these problems. Instead, after medical evaluation, he was found to have hyperthyroidism without any underlying heart disease. The appropriate tests were ordered and a diagnosis of Graves’ disease was established. As often happens, control of the patient’s hyperthyroidism helped normalize his heart rhythm. The former President remained free of atrial fibrillation for ten years once his thyroid condition was stabilized.
Today, physicians test for hyperthyroidism in anyone who develops atrial fibrillation. In one research study, atrial fibrillation was found in 25% of individuals who had developed hyperthyroidism over the age of 60. It is important to recognize atrial fibrillation when it occurs and to initiate appropriate treatment. Atrial fibrillation is caused by a rapid, erratic contraction pattern in the upper chambers of the heart which leads to an irregular pulse, a fall in the output of blood from the heart, and an increase in the tendency for blood to clot in the upper chambers of the heart. This tendency to cause clotting has led to atrial fibrillation being recognized as an important cause of stroke. Therefore, recognizing atrial fibrillation and treating it appropriately is mandatory. Patients who experience rapid, uncomfortable palpitation should seek medical advice immediately. While hyperthyroidism is not a common cause of atrial fibrillation, a high proportion of patients with hyperthyroidism do develop atrial fibrillation. Fortunately, treatment of the hyperthyroidism, as was the case with President Bush, will often help bring the atrial fibrillation under control and indeed may prevent future recurrences. You have a 50% chance of this happening if you are younger than 50 and 25% if you are older than 60.
Unfortunately, there is evidence that individuals who have had hyperthyroidism in the past and have been cured and now have normal thyroid function may still have an increased risk for atrial fibrillation relative to the rest of the population. Thus, by age 70, 10% of individuals with a history of hyperthyroidism have atrial fibrillation while only 5% of those who lack a history of a thyroid problem have the condition. A combination of factors may explain these observations. Excess thyroid hormone stimulates the heart to go faster and may precipitate irregular heart rhythm disturbances, particularly in patients who are predisposed to this occurring.
If you develop atrial fibrillation, the first medicines that are given will be medicines to reduce the rapid pulse rate. These include beta-blockers such as atenolol, nadolol, and metoprolol (Toprol). Other drugs such as calcium-channel blockers (verapamil, diltiazem) and digoxin may also be used. These medicines all will slow the pulse down in atrial fibrillation when the pulse is rapid. Additionally, when you first present, the doctor may well prescribe an intravenous clot-preventing medicine such as heparin. Once the condition has been stabilized, your physician will likely prescribe pills such as the medicines described above to slow down the heart rate chronically and also will likely prescribe a medicine to make it more difficult for your blood to clot. The most important treatment in many respects for atrial fibrillation is prevention of blood clots which can be propelled from the heart where they form and cause a stroke, which is damage to an area of the brain. These blood clots can go elsewhere in the body as well, but clots traveling to the brain are the most serious consequence of atrial fibrillation. There are medicines that your physician can prescribe that will reduce the likelihood of this occurring. These include aspirin and warfarin (Coumadin). Aspirin works as a mild anticoagulant while warfarin is more effective at preventing strokes, but is also a more difficult medicine to use. If you are given warfarin, your doctor will have your blood checked periodically to be sure that the amount of anticoagulation is enough to prevent clots but yet not thin your blood too much which would increase the risk of bleeding either spontaneously or when you cut or injure yourself. Your doctor will give you specific instructions on how often your blood should be tested to assess the warfarin effect. It is very important that you follow the instructions precisely if you are taking warfarin and that you educate yourself about other medicines that may interact with warfarin that you need to avoid. A review of some of these relationships can be found at www.Coumadin.com. You should also notify your physician if there are signs of increased bruising or bleeding from any sites such as nosebleeds or bleeding with bowel movements. In patients with hyperthyroidism who develop atrial fibrillation, fortunately these treatments may only be necessary for a short while until the thyroid comes under control. At that time, it may be possible to withdraw medicines to control the heart rhythm and also medicines to prevent blood clotting. Any decision to withdraw medicine, though, must be made by your physician in consultation with you.
There is a medication, amiodarone (Cordarone), that is commonly used to treat atrial fibrillation that may itself cause thyroid disorders, either an overactive or an underactive thyroid gland. Thus, in patients who are being followed on treatment with amiodarone, routine testing of thyroid function by blood testing is wise. This will allow early diagnosis and treatment of the thyroid disorder. Sometimes, hyperthyroidism cannot be treated without discontinuing amiodarone, while in other patients amiodarone may be continued while antithyroid medications are prescribed simultaneously. Radioactive iodine is ineffective in patients treated with amiodarone since amiodarone contains a lot of iodine and saturates the thyroid gland preventing uptake of additional iodine. Hypothyroidism induced by amiodarone can usually be managed by giving thyroid hormone replacement and continuing amiodarone therapy.
If you are interested in learning more about atrial fibrillation and its treatments, the web site www.affacts.org is a rich resource concerning this problem.
Children born to mothers with hypothyroidism did less well on a variety of intelligence tests, and had an average IQ that was 7 points lower.