A 58-year-old woman with metastatic ovarian cancer presents with acute dyspnea and chest pain. A CT pulmonary angiogram (CTPA) is performed. The structures marked **B** (right and left pulmonary arteries) show a hypodense intraluminal filling defect with partial occlusion of the right pulmonary artery and complete occlusion of the left. The right ventricle is dilated (RV:LV ratio 1.2). Which of the following best describes the clinical risk stratification and immediate management approach for this patient?