Chemotherapy Is Not Always the Culprit

A 32-year-old female patient presents to the cardiology clinic for evaluation of syncope that occurred 10 days ago at home while she was walking to the bathroom. The event was witnessed by her boyfriend who reported the syncopal episode lasting only for a few seconds and was without tonic-clonic limb movement. She did not experience any prodromal symptoms such as palpitations, chest discomfort, or aura. She denies any subsequent confusion, incontinence, or head injury. She has no history of syncope or palpitations. Her family history is negative for syncope or sudden cardiac death. She was initially evaluated by her hematologist and then referred to cardiology clinic.

She has a history of large B-cell lymphoma and completed cycle 3 of dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin, rituximab (EPOCH-R) chemotherapy regimen the day prior to her syncopal episode. She recently completed a 1-week duration of acyclovir 400 mg BID, fluconazole 200 mg per day, and levofloxacin 500 mg per day as prophylaxis of infection during chemotherapy-induced neutropenia 3 days ago. She is on allopurinol 300 mg per day as prophylaxis for hyperuricemia. She is on subcutaneous enoxaparin 120 mg BID for right upper extremity deep vein thrombosis. She also takes lansoprazole 30 mg BID for gastroesophageal reflux disease.

On examination, she is afebrile with a heart rate of 94 bpm, blood pressure of 121/81 (without orthostasis), and a respiratory rate of 16 breaths per minute with an oxygen saturation of 100% on room air. She is alert and oriented, non-toxic appearing and in no distress. Her heart has regular rate and rhythm without murmur, normal S1 and S2, and a non-displaced point of maximal impulse. Her lungs are clear on auscultation bilaterally; her abdominal exam is unremarkable; and her extremities are without cyanosis, clubbing, or edema. An electrocardiogram (ECG) performed 1 week ago revealed sinus rhythm and QTc of 551 ms. An ECG repeated in our cardiology clinic revealed sinus rhythm and QTc of 443 ms. A transthoracic echocardiogram demonstrated a normal left ventricular size and function and no valvular abnormalities. Laboratory values are all within normal range.

What is the most likely culprit of the patient's prolonged QT?

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