ECG — Digoxin Toxicity Sagging ST + Bidirectional VT

A 68-year-old man with chronic atrial fibrillation and heart failure presents to the emergency department with severe nausea, visual disturbances (yellow-green halos around lights), and palpitations. His ECG shows the pattern marked **A** — sagging "reverse tick" ST depression with bidirectional ventricular tachycardia. Serum potassium is 5.8 mmol/L (normal 3.5–5.0). He has been on digoxin 250 μg daily for 2 years; his creatinine is 1.8 mg/dL (eGFR ~35 mL/min/1.73m²). Which of the following is the most appropriate immediate management?