A 54-year-old man is transferred to the hospital from his cardiologist's office due to atrial fibrillation with rapid ventricular response. His symptoms began 24 hours earlier with palpitations, lightheadedness, and chest tightness. The patient has had similar episodes several times during the last year. Past history is notable for mitral valve repair 3 years ago for severe symptomatic mitral regurgitation. The patient undergoes direct current cardioversion due to worsening hemodynamic instability, with resolution of the arrhythmia and all associated symptoms. He is considered for long-term amiodarone therapy to prevent future arrhythmic episodes. Which of the following should be tested before initiating this medication?
Major adverse effects of amiodarone | |
Cardiac |
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Pulmonary |
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Endocrine |
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Gastrointestinal/ |
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Ocular |
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Dermatologic |
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Neurologic |
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Amiodarone is a class III anti-arrhythmic agent used to suppress life-threatening rhythm disturbances. Because it is 40% iodine by weight, amIODarone can cause a number of alterations in thyroid function. It can cause hypothyroidism due to decreased production of thyroid hormone. Individuals with pre-existing autoimmune thyroid disease are at greatest risk and so should be screened for subclinical hypothyroidism with a serum TSH assay prior to initiating amiodarone therapy. Amiodarone can also cause hyperthyroidism due to increased thyroid hormone synthesis or destructive thyroiditis with release of preformed thyroid hormone.
(Choices A and B) Amiodarone is not associated with altered function of the adrenal cortex or medulla.
(Choice C) The oral glucose tolerance test is used to screen for diabetes mellitus, primarily in pregnant women. Amiodarone is not associated with significant alterations in insulin sensitivity or blood glucose levels.
(Choice D) Release of prolactin is primarily regulated by inhibitory effects of dopamine from the hypothalamus. Release is stimulated to a small degree by thyrotropin-releasing hormone and therefore may be mildly affected by amiodarone. However, these effects would not be clinically significant.
(Choice E) Amiodarone can cause erectile dysfunction, which may be related to its alpha and beta adrenoreceptor blocking effect. Amiodarone does not significantly alter serum testosterone levels.
Educational objective:
Amiodarone is 40% iodine by weight. It can cause hypothyroidism due to decreased production of thyroid hormone. Amiodarone can also cause hyperthyroidism due to increased thyroid hormone synthesis or destructive thyroiditis with release of preformed thyroid hormone.