A case of Amiodarone-induced hypothyroidism complicated by Torsades de Pointes.
Journal of the American College of Cardiology
ackground: Amiodarone is a class III antiarrhythmic drug that is commonly used for management of tachyarrhythmias. Amiodarone-induced hypothyroidism is a well-established side effect; however severe hypothyroidism presenting with torsades de pointes (TdP) is an underappreciated complication. Case: A 69-year-old female with history of hypothyroidism (on levothyroxine) and paroxysmal atrial fibrillation status post amiodarone chemical cardioversion and rate control with digoxin presented to the emergency department with syncope. Her heart rate was noted to be 18 beats per minute and her EKG was significant for junctional bradycardia and QTc interval of 744 ms. Initial labs revealed K: 3.6 mg/dL, Mg: 1.9 mg/dL, TSH: 76.59 uIU/mL, digoxin level of 2.3 ng/mL, Cr: 3.1 mg/dL (baseline 1.3 mg/dL). Echocardiogram showed a ventricular ejection fraction of 45%. She developed episodes of ventricular tachycardia complicated by torsades de pointes requiring emergent cardioversion. Transvenous pacer was placed, intravenous amiodarone initiated, and digoxin held. She continued to be pacer-dependent despite correction of electrolyte abnormalities and normalization of digoxin level. Amiodarone was then discontinued due to concerns with effects on hypothyroidism. She received a permanent pacemaker prior to discharge. Decision-making: As a cardiology clinical pharmacist, I reviewed her chart and noted that TSH was significantly increased (from 5 to 62 uIU/mL) approximately 1 year after initiation of amiodarone, a well-recognized complication of chronic use. Conclusion: Amiodarone is 30% iodine by molecular weight. This leads to inhibition of T4 metabolism in the liver and pituitary with subsequent decrease in serum T3 with normal serum TSH. Chronic treatment rises total iodine content of body which ultimately inhibits the synthesis of T4 with resultant elevation of TSH. The overall prevalence of amiodarone-induced hypothyroidism is 15-20%. Thyroid function should be measured at baseline and frequently thereafter while on amiodarone.
9 Supplement 1
Daneshvar, Farzad; Patel, Arpan; and Mahmood, Raai, "A case of Amiodarone-induced hypothyroidism complicated by Torsades de Pointes." (2019). Articles. 319.