A 55-year-old woman presents with sudden onset pleuritic chest pain and dyspnoea. She had a knee replacement 2 weeks ago. RR is 26 breaths/min, HR 110 beats/min, BP 120/75 mmHg, SpO2 93% on room air. What is the most appropriate next investigation?AD-dimer assayBVentilation-perfusion scan or CT pulmonary angiography depending on availabilityCTransthoracic echocardiogram onlyDChest X-ray onlyENo imaging, treat empirically with antibioticsCheck my answer