A 62-year-old woman with a history of metastatic lung cancer (on chemotherapy) presents with sudden-onset dyspnea, syncope, and chest discomfort. On examination, blood pressure is 85/55 mmHg, heart rate 125/min, JVD is prominent, and right ventricular heave is palpable. Oxygen saturation is 88% on room air. ECG shows sinus tachycardia with right axis deviation and T-wave inversion in leads III and aVF. Bedside echocardiography reveals dilated right ventricle with reduced RV function and McConnell sign. What is the most appropriate immediate management?