Dofetilide Initiation With Borderline QTc and Renal Impairment
A 71-year-old woman with symptomatic persistent atrial fibrillation and heart failure with preserved ejection fraction (LVEF 52%) is admitted for dofetilide initiation after amiodarone was stopped because of thyrotoxicosis. Her medications are furosemide 40 mg daily, lisinopril 10 mg daily, metoprolol succinate 50 mg daily, and apixaban 5 mg twice daily. Laboratory values: creatinine 1.6 mg/dL, estimated creatinine clearance 38 mL/min, potassium 3.6 mmol/L, magnesium 1.8 mg/dL, and QTc 452 ms with a QRS of 96 ms. She has been in atrial fibrillation for 3 months and is adequately anticoagulated. She weighs 68 kg and has no history of ventricular arrhythmia. The nurse asks whether the first dose can be given now and what monitoring is required. The patient is eager to avoid another ablation because she cares for her husband, who has dementia.
1. Is this patient eligible for dofetilide initiation today, and what would you do before the first dose?
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No. The baseline QTc is 452 ms and her QRS is 96 ms, so she does not meet the ventricular conduction abnormality exception; dofetilide is contraindicated when baseline QTc exceeds 440 ms. In addition, her potassium is 3.6 mmol/L, which is too low for a QT-prolonging drug; I would replete potassium to at least 4.0 to 4.5 mmol/L and magnesium to at least 2.0 mg/dL before reconsidering. Her creatinine clearance is 38 mL/min, so if she were eligible the dose would be 125 mcg twice daily, not 250 or 500 mcg. I would also review interacting drugs: she is not on verapamil, diltiazem, ketoconazole, trimethoprim, or hydrochlorothiazide, but furosemide can worsen hypokalemia and should be monitored. Because the QTc is a hard contraindication, I would not give the first dose and would instead discuss alternatives: catheter ablation, a different antiarrhythmic with less QT risk, or rate control.
2. If her QTc were 430 ms after potassium repletion, outline the initiation and monitoring plan and the stopping rules.
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With a QTc of 430 ms, normal QRS, and potassium above 4.0, she would be eligible for inpatient initiation. I would calculate creatinine clearance and give 125 mcg twice daily for her CrCl of 38 mL/min. I would obtain a 12-lead ECG 2 to 3 hours after each dose, continuously monitor telemetry for at least 3 days, and check potassium and magnesium daily. The first dose should be given in a monitored setting with resuscitation equipment. I would reduce the dose if QTc increases by more than 15% from baseline or exceeds 500 ms; I would stop the drug if QTc remains above 500 ms after dose reduction or if torsades develops. I would avoid drugs that prolong QT or inhibit renal secretion of dofetilide, and I would not discharge before 3 days of stable telemetry. I would also ensure anticoagulation and arrange follow-up ECG within 1 week.