A 42-year-old woman with newly diagnosed hypertension is started on verapamil for blood pressure control. One week later, she presents with severe bradycardia (HR 38 bpm), hypotension (BP 88/56 mmHg), and syncope. ECG shows a prolonged PR interval (280 ms) and first-degree atrioventricular block. She denies chest pain or dyspnea. What is the most appropriate immediate next step in management?