Question

A 54-year-old woman is evaluated in the outpatient pulmonary clinic for a 6-month history of progressive shortness of breath with exertion. She reports no chest pain, orthopnea, or syncope. She has a history of unprovoked deep vein thrombosis 3 years ago, for which she completed 6 months of anticoagulation therapy. Her current medications include a daily multivitamin. Vitals show a blood pressure of $128/82$ mm Hg, pulse of $88$/min, and respiratory rate of $18$/min. Pulse oximetry is $96\%$ on room air. Physical examination reveals clear lung fields bilaterally. Cardiac examination demonstrates a parasternal heave and a prominently split $S_2$ with a loud pulmonic component. Transthoracic echocardiography reveals right atrial and right ventricular enlargement, flattened interventricular septum during systole, and an estimated right ventricular systolic pressure of $65$ mm Hg. Left ventricular ejection fraction is $60\%$ with normal diastolic function. Which of the following is the most appropriate next step in the diagnostic workup of this patient?