A 45-year-old woman presents with pleuritic chest pain and haemoptysis. She has a history of deep vein thrombosis and has been on warfarin therapy. On examination, she is tachycardic, mildly hypotensive, and hypoxic. CT pulmonary angiography shows a large saddle pulmonary embolus with right ventricular dilation. According to current guidelines, which treatment is most appropriate?