Introduction: Tacrolimus is a calcineurin inhibitor commonly used for immunosuppression in transplant recipients. It can be nephrotoxic, and acute or chronic kidney injury leads to higher mortality rates. Hyperkalemia is a known complication with need for careful lab monitoring, as untreated hyperkalemia can lead to sinus bradycardia, sinus arrest, and asystole, especially in transplant recipients exposed to multiple interacting medications. Description: A 64-year-old woman with history of bilateral lung transplant for interstitial lung disease secondary to rheumatoid arthritis, recently diagnosed with pancytopenia and posttransplant lymphoproliferative disorder with initiation of chemotherapy (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) roughly 2 months prior, was transferred to our facility after a syncope event secondary to symptomatic bradycardia. She was hypotensive on arrival and given 2 doses of atropine without response. Hyperkalemia (potassium, 7.9 mEq/L) and acute kidney injury (creatinine, 2.61 mg/dL) were discovered. Electrocardiogram (ECG) demonstrated sinus bradycardia with tall, peaked T-waves eventually progressing to sinus arrest with need for emergent insertion of a transvenous pacemaker (TVP) for ventricular rates in the 20-30s; TVP was set at VVI 50 bpm. Her tacrolimus level was supratherapeutic at 17.7 ng/mL, contributing to worsening renal function and hyperkalemia. TVP was removed after 3 days due to prompt correction of electrolytes and renal function and medication changes with return of sinus rhythm. On review, the syncopal episode was a sequel of ongoing arrhythmias in the setting of ongoing hyperkalemia. Discussion: ECG changes seen with hyperkalemia progress gradually with increasing serum levels of potassium. Initial changes include peaked T waves and QT shortening, which progress to prolonged QRS/QT intervals and finally sinus arrest, sinus bradycardia, and asystole. This case highlights the critical importance of close monitoring of transplant recipients on nephrotoxic and potassium-altering medications. Early recognition and management of hyperkalemia are essential to prevent life-threatening arrhythmias such as sinus arrest.
Bruce et al. (Sun,) studied this question.