A 40-year-old man presents to the Emergency Department confused and agitated. His partner reports he took an unknown quantity of his amitriptyline tablets about 2 hours ago. On examination, his heart rate is 130 bpm, BP 100/60 mmHg, respirations 20/min, temperature 37.8°C. His pupils are dilated, and skin is flushed and dry. ECG shows sinus tachycardia with a QRS duration of 130 ms. What is the most important immediate treatment specific to tricyclic antidepressant toxicity?