MSFinals-0370

MSFinals-0370

A 32-year-old woman who has recently returned from holiday to Australia presents to the Emergency Department with sudden-onset chest pain and shortness of breath. The patient has no medical history of note and takes no medication, apart from the combined oral contraceptive pill (COCP).
On examination, the patient is significantly breathless at rest, with a respiratory rate of 30 breaths/min. Oxygen saturations are 91% on high-flow oxygen; her blood pressure is 105/65 mmHg, and her heart rate is 110 bpm and regular. Her temperature is 37.5 °C.
On examination of the chest, breath sounds are normal, with good air entry. No focal signs are found.
Which of the following investigations would be the most appropriate to confirm the likely diagnosis?