Abnormal thyroid function
Thyroid disease is a common disorder and is also a risk factor for developing or worsening of heart failure. Abnormal function of the thyroid gland (located in the front of your neck) can be of two kinds: it may produce too much or too little thyroid hormones. Thyroid hormones regulate cellular metabolism and sends a message to cells making them either speed up or slow down.
The symptoms of overactive thyroid include rapid heartbeat, heat and exercise intolerance, shortness of breath on exertion, increased perspiration, weight loss and profound weakness. An excess of thyroid hormone exerts strain on the heart muscle, increases pumping function and frequently causes the common heart rhythm disturbance AF.
In contrast, when the thyroid gland is underactive and produces too little hormone, typical features are weight gain, cold intolerance, slow heart rate, decreased pumping function, weakness, an increase in cholesterol level which contributes to coronary artery disease.
If a thyroid disorder is suspected, the diagnosis is based on a routine test and an analysis of thyroid hormones in the blood. Sometimes, it is necessary to examine the thyroid gland using an imaging/scanning technique to make sure that no further intervention is required. Correction of thyroid function is essential in providing optimal treatment for patients with coexisting heart failure. In the case of overproduction (hyperthyroidism), the physician will often prescribe medications which can slow down the production of thyroid hormones. Beta-blockers are especially useful to control heart rate when too much thyroid hormone is produced. Conversely, if thyroid production is inadequate (hypothyroidism), medications are administered to increase the amount of thyroid hormone in the blood.
Certain drugs used to regulate heart rhythm for patients with heart failure, contain significant amount of iodine. Most importantly, amiodarone which is commonly used for several types of rhythm disturbance, can induce various types of thyroid malfunction which may be either overactive or underactive. Therefore, while using amiodarone it is important to watch for changes in weight, heat or cold intolerance, palpitations or worsening angina. It is recommended that thyroid function is assessed routinely with a blood test in patients on long-term therapy with amiodarone. If the levels are abnormal, your doctor will need to decide whether or not to discontinue amiodarone therapy and recommend another drug to replace it if required. Amiodarone can also cause photosensitivity and a characteristic skin discoloration. Mild disturbances will usually return to normal after discontinuation of amiodarone treatment.