A 72-year-old woman with a history of atrial fibrillation (not on anticoagulation) and recent hospitalization for pneumonia (discharged 3 days ago) presents with sudden onset dyspnea and syncope. On arrival, vital signs are: BP 88/54 mmHg, HR 118/min, RR 32/min, SpO₂ 85% on room air, JVP elevated at 8 cm H₂O. Bedside echocardiography shows acute right ventricular dilatation with RV/LV ratio >0.9 and McConnell's sign. Troponin I is elevated at 0.15 ng/mL. What is the most appropriate immediate management?