Review Question - QID 104197

A 62-year-old man is brought to the emergency room with a chief complaint of chest pain. The patient states that the pain started 2 hours ago and is most severe in the middle of his chest. The pain feels "squeezing" in quality and does not improve or worsen with position. The patient has a history of diabetes for which he takes metformin. He has not had any prior surgeries. He has been a 1.5-pack-per-day smoker for the last 30 years. He drinks alcohol socially and does not use illicit drugs. The patient's temperature is 99.0°F (37.2°C), blood pressure is 140/95 mmHg, pulse is 105/min, and respirations are 20/min. Physical exam reveals a normal S1 and S2 without additional heart sounds. His lungs are clear to auscultation. There is no tenderness to palpation of the chest. An ECG is shown in Figure A. The patient is given the appropriate pharmacologic treatment for his condition. Soon after, the patient states that he is having trouble breathing. Which of the following is most likely responsible for the symptoms experienced by this patient?