A 63-year-old man presents to the emergency department with sudden onset pleuritic chest pain and shortness of breath. He had a total hip replacement 2 weeks ago. He is tachycardic at 112 beats/min, RR 24/min, BP 118/74 mmHg and SpO2 90% on air. His Wells score suggests a high probability of pulmonary embolism. What is the most appropriate next step in management?