A 59-year-old man presents with acute onset pleuritic chest pain and shortness of breath. He is hypotensive at 80/50 mmHg, heart rate 125/min, respiratory rate 30/min and oxygen saturation 86% on room air. CT pulmonary angiography shows a large saddle pulmonary embolus with right ventricular strain. According to contemporary pulmonary embolism management guidelines, what is the most appropriate immediate therapy?