A 38-Year-Old Woman Comes to the Office Due to Dyspnea

A 38-year-old woman comes to the office due to dyspnea on exertion for the past 6 months.  She says, "I get out of breath even when I walk less than a block at my usual pace.  I climb stairs very slowly."  A year ago, the patient was able to walk 10-12 blocks without any limitations.  She has no chest pain, palpitations, syncope, cough, or hemoptysis.  She has no medical problems.  The patient saw a doctor 2 years ago and had a routine physical that did not show any abnormalities.  She does not use tobacco, alcohol, or illicit drugs.  Her mother has a history of breast cancer and "blood clots" in her legs.  Her father had a stroke.  The patient takes no prescription or over-the-counter medications.  She has no known drug allergies.  On examination, she appears comfortable at rest.  Temperature is 36.7 C (98 F) , blood pressure is 143/91 mm Hg, pulse is 84/min, and respirations are 16/min.  Pulse oximetry shows 94% saturation on room air.  BMI is 34 kg/m².  On cardiac auscultation there is a prominent S2 but no murmurs or additional sounds.  The lungs are clear.  Peripheral pulses are full and no finger or toe clubbing is present.  There is no peripheral edema.  Chest-x ray reveals prominent pulmonary arteries but no infiltrates.  ECG reveals normal sinus rhythm with right axis deviation.
Which of the following is the most appropriate next step in management of this patient?

A) ECG stress test
B) Echocardiography
C) High-resolution CT scan of the chest
D) Polysomnography
E) Ventilation/perfusion scan