Management of Atrial Flutter in Thyroid Storm

Introduction: Thyroid storm, life-threatening hyperthyroidism, commonly presents with tachyarrhythmias. We present a case of hyperthyroid-induced atrial flutter, refractory to beta-blockade, successfully treated with electrical cardioversion (CV) while biochemically hyperthyroid. Case Description: A 49-year-old female with history of asthma and no family or personal history of thyroid disease presented with new-onset atrial flutter and heart failure. The patient endorsed weight loss, hot flashes, anxiousness, tremors, and palpitations. She denied gastrointestinal symptoms or visual changes. She was afebrile with normal mentation. Heart rate was found to be 260 beats per minute (bpm) in atrial flutter. Exam demonstrated bilateral lower extremity edema, and profound exophthalmos. Labs were remarkable for thyroid stimulating hormone (TSH) <0.01 [ref: 0.27-4.2] uIU/mL, free T4 4.5 [ref: 0.8-1.8] ng/dL, free T3 15.5 [ref: 2.0-4.4] pg/mL, thyroid stimulating immunoglobulin (TSI) of 379 [ref: <140] % and a thyroid receptor antibody (TRab) of 10.02 [ref:<=2.0] IU/L. White blood cell count and liver function tests were normal. Chest x-ray (CXR) showed bilateral pulmonary edema and ultrasound showed an enlarged heterogeneous hypervascular thyroid gland. The patient was initially started on Methimazole 30 mg daily and Metoprolol 25 mg every six hours but on day two, the patient was transitioned to Propylthiouracil (PTU) 250 mg every 6 hours given continued atrial flutter and concern for thyroid storm given Burch-Wartofsky score was 50. She was also given potassium iodide for three days. Cardioversion was deferred, as it was felt that the severity of thyrotoxicosis would limit success. On day six, TFTs were improved with a free T4 of 2.2, free T3 3.6. On day 8, because of continued tachycardia >130 bpm with limitation of beta-blockade due to hypotension, she underwent a cardioversion which was successful. On discharge, free T4 was 1.7 and she was transitioned to Methimazole 40 mg daily. Discussion: Thyroid storm has a mortality rate of 10-20%, often related to tachyarrhythmias which can be difficult to treat during a hyperthyroid state. Tachycardia should initially be treated with beta-blockade and antithyroid therapy. Amiodarone is avoided due to concern for worsening hyperthyroidism. A literature review suggests that electrical CV should not be attempted until a patient is euthyroid for four months, as a majority will spontaneously revert once thyroid levels normalize. Conversely, other studies have found that the rate of recurrence of atrial fibrillation between clinically hyperthyroid and euthyroid patients was not statistically significant, suggesting CV should not be delayed until a patient is euthyroid. This suggests that further studies need to be completed to better elucidate appropriate timing in hyperthyroid patient’s refractory to pharmacologic treatment alone.