Monday, February 6, 2012

Hyperthyroidism and Your Heart Health: What you should Know

In hyperthyroidism, caused by the overproduction of thyroid hormone, the heart muscle is "whipped" like a horse, and for a person with heart disease it's like whipping a tired horse. Thyroid hormone increases the force of contraction of, and the amount of oxygen demanded by, the heart muscle. It also increases the heart rate. For these reasons the work of the heart is greatly increased in hyperthyroidism. Hyperthyroidism increases the amount of nitric oxide in the lining of the blood vessels, causing them to dilate and become less stiff.
Cardiac symptoms of hyperthyroidism
Cardiac symptoms can be seen in anybody with hyperthyroidism, but can be particularly dangerous in people with underlying heart disease. Common symptoms include:
·         Fast heart rate (tachycardia) and palpitations. Occult 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 the diagnosis of Inappropriate Sinus Tachycardia. Especially in patients with underlying heart disease, hyperthyroidism can also produce a host of other arrhythmias such as Premature Ventricular Complex (PVC’s) ,  ventricular tachycardia and especially atrial fibrillation. Indeed, it is important to rule out hyperthyroidism in a patient with atrial fibrillation and no clear underlying cause.

·         Systolic hypertension. The forceful cardiac contraction increases the systolic blood pressure, though the increased relaxation in the blood vessels reduces the diastolic blood pressure.

·         Shortness of breath on exertion. This can be due to the skeletal muscle weakness cause by hyperthyroidism, or to a worsening in heart failure.

·         Heart failure. Hyperthyroidism itself can produce heart failure, but this condition is relatively rare. On the other hand, if pre-existing heart disease is present, worsening of heart failure with hyperthyroidism is common, and can be extremely difficult to treat.

·    Worsening angina. Patients with coronary artery disease often experience a marked worsening in symptoms with hyperthyroidism. These can include an increase in chest pain (angina) or even a heart attack.

As with hypothyroidism, hyperthyroidism can be present - and often is - without the classic, textbook symptoms. So patients with any of these cardiac symptoms that cannot otherwise be readily explained should have thyroid function measured. Furthermore, sometimes a "mild" hyperthyroidism can exist in which thyroid blood tests can be misinterpreted. In these cases thyroid hormone levels themselves are normal, but the level of thyroid stimulating hormone (TSH - a hormone excreted by the pituitary gland that regulates the thyroid gland) is low. 

A low TSH indicates hyperthyroidism, despite "normal" thyroid hormone levels. This pattern of thyroid blood tests especially ought to be sought in all patients displaying any of the above symptoms with no clear reason for them.
Treating hyperthyroidism
The "best" way of treating hyperthyroidism is controversial. In the U.S., most doctors immediately opt for ablating the overactive thyroid gland with radioactive iodine, then giving the patient thyroid hormone pills since the thyroid gland is no longer functional. This method is certainly "easiest" for the doctors, but often patients are left feeling chronically abnormal. Using drugs to partially suppress the thyroid gland - in the U. S., Tapazole or PTU - creates somewhat more of a long-term management issue for doctors, but may lead to ultimately happier patients.

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