A 45-year-old woman has had progressive fatigue, shortness of breath, and menorrhagia for 6 months. She reports feeling cold most of the time. Her voice is deep and hoarse. The thyroid gland is normal in size, crackles are heard at both lung bases, and muscle stretch reflexes at the ankles have a delayed relaxation phase. Hematocrit is 31%, and mean corpuscular volume is 74 μm3. X-ray of the chest shows an enlarged globular heart. Which of the following studies is most likely to establish the diagnosis?
A) Bone marrow aspiration and biopsy
B) Echocardiography
C) Laryngoscopy
D) Pap smear
E) Thyroid-stimulating hormone