A 71-year-old man presents with three days of dyspnoea. CT pulmonary angiography shows bilateral pulmonary emboli and right ventricular enlargement; his blood pressure is 128/76 mmHg, and he has no syncope or shock. His troponin concentration is raised, and his estimated glomerular filtration rate is 22 mL/min/1.73 m² (reference range greater than 60). Which one of the following is the most appropriate initial treatment?