Q. A 65-year-old female presents to the emergency department with a primary complaint of dyspnea. She reports her symptoms have progressed over the past 24 hours. Additionally, she reports fatigue and swelling in her legs and ankles for the past week. The patient denies any chest pain or other associated symptoms. Her past medical history is significant for diabetes, hypertension, rheumatoid arthritis, and hyperlipidemia. On physical examination, she is afebrile, weighs 75 kg (165 lb), her blood pressure is 170/100 mm Hg, heart rate 90/min, respiratory rate 20/min, and oxygen saturation is 94 percent on 2L of oxygen via nasal cannula. Evaluation of her neck reveals a significant clue to her diagnosis (see image). Assessment of her chest demonstrates a laterally displaced apex beat and a third heart sound audible on auscultation. Otherwise, her lungs are clear. She also has 2 plus pitting edema bilaterally up to her knees. You order a chest x-ray and electrocardiogram. Which of the following blood tests is most likely elevated in this patient secondary to her diagnosis?