A 54-year-old woman presents to the emergency department with pleuritic chest pain and shortness of breath. Her heart rate is 120 bpm, respiratory rate 28/min, BP 110/70 mmHg, and oxygen saturation 90% on air. Her two-level Wells score for pulmonary embolism (PE) is ”PE likely”. She is haemodynamically stable. What is the most appropriate next step?