MRCP2-0530

A 56-year-old woman presents to the emergency department complaining of sudden shortness of breath and slight pleuritic chest pain. She denies coughing up any blood and feeling hot or cold. Her symptoms started four hours ago while she was at rest. She has a medical history of hypothyroidism and underwent a wide local excision for ductal carcinoma in situ a year ago. The patient has never smoked and was previously healthy. On examination, scattered crepitations are heard over the right lower zone, and her oxygen saturation is at 93%. Blood tests, including a D-dimer, are pending. What is the most appropriate next step?