A 46-year-old man presents to the emergency department for a complaint of dyspnea on exertion for the past 6 days. He reports feeling of pressure on his chest and a feeling of lightheadedness which began 2 hours ago while he was walking. He has a past medical history of hypertension which is managed with lisinopril. He has a 20 pack-year smoking history. Family history is unremarkable. Vital signs reveal bradycardia with a normal blood pressure. Physical examination reveals bradycardia but is otherwise unremarkable. An electrocardiogram (ECG) reveals evidence of inferior wall ischemia and bradycardia indicating dysfunction of the sinoatrial (SA) node.

An occlusion of which of the following blood vessels is most likely responsible for his current condition?

• A) Left anterior descending artery
• B) Left coronary artery
• C) Posterior descending artery
• D) Right coronary artery
• E) Superior vena cava