A 48-year-old woman on ICU develops pulseless ventricular tachycardia. After successful defibrillation and ROSC, she is in a regular broad-complex tachycardia at 180 bpm with a BP of 95/60 mmHg. She is drowsy but responsive. An amiodarone infusion is commenced. Two hours later, the rhythm changes to a regular narrow-complex tachycardia at 160 bpm with absent P waves and an irregular baseline. What is the most likely rhythm?