Review Question - QID 108609

A 34-year-old woman presents to the emergency room with chest pain. She has a sensation of something being stuck in her chest, and this is the 3rd episode in the last month. The prior 2 incidents occurred at the gym while she was drinking a sports drink and resolved after resting for 3-4 minutes. This episode started after she received news that her father had a heart attack at age 69. This episode lasted for 15 minutes. The patient also notes several months of intermittent difficulty swallowing but denies palpitations, diaphoresis, or shortness of breath. She has a past medical history of obesity and longstanding gastroesophageal reflux disease (GERD) for which she takes omeprazole daily. The patient has a family history of scleroderma in her mother. She does not smoke cigarettes, drinks alcohol socially, and does not use drugs. Her temperature is 98.4°F (36.8°C), blood pressure is 143/82 mmHg, pulse is 89/min, and respirations are 16/min. The patient appears mildly uncomfortable but is in no acute distress. There is a normal S1 and S2 on cardiac auscultation without murmurs or gallops. Her lungs are clear bilaterally. Which of the following is the most appropriate confirmatory test?