A 58-year-old man presents to the emergency department with acute-onset dyspnea, chest pain, and syncope. On examination, he is hypotensive (BP 85/52 mmHg), tachycardic (HR 118/min), and confused. A CT pulmonary angiogram shows a large thrombus straddling the bifurcation of the main pulmonary artery and extending into both the right and left main pulmonary arteries, as marked by **A** in the diagram. Which of the following is the most appropriate immediate management for this patient?