This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'A 70-year old male patient presented to the emergency department with pain in epigastrium and difficulty in breathing for 6 hours. On examination, his heart rate was 56 beats per minute and the blood pressure was 106/60 mm Hg. Chest examination was normal. The patient has been taking omeprazole for gastroesophageal reflux disease for last 6 months. What should be the intial investigation - \nSelect and explain. \nA. An ECG, B. An upper GI endoscopy, C. Urgent ultrasound of the abdomen, D. An x-ray chest', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]