Question

A $61$-year-old woman presents to the emergency department with a $1$-day history of sharp right-sided chest pain that worsens with deep inspiration, accompanied by progressive shortness of breath. She has a history of type 2 diabetes mellitus, hypertension, and stage 4 chronic kidney disease. Her current medications include amlodipine, insulin glargine, and atorvastatin. Temperature is $37.1^\circ\text{C}$ ($98.8^\circ\text{F}$), blood pressure is $138/82\text{ mmHg}$, pulse is $114/\text{min}$, and respirations are $22/\text{min}$. Pulse oximetry shows $92\%$ on room air. BMI is $34\text{ kg/m}^2$. Physical examination is notable for mild swelling and tenderness in the right calf. Laboratory testing shows a serum creatinine of $2.9\text{ mg/dL}$ (baseline $2.7\text{ mg/dL}$) and an estimated creatinine clearance of $17\text{ mL/min}$. Computed tomography pulmonary angiography demonstrates a filling defect in the right lower lobe pulmonary artery. Transthoracic echocardiography reveals normal right ventricular size and function. Which of the following is the most appropriate initial pharmacologic intervention?