A 69-year-old man complains of tightness in the chest and shoness of breath after lifting boxes 3 hours ago. He perceives that his hea is skipping beats. His medical history is significant for hypeension and cigarette smoking. On examination, his hea rate is 50 beats/min and regular, and his lungs are clear to auscultation. An electrocardiogram shows bradycardia with an increased PR interval and ST-segment elevation in multiple leads including the anterior leads, V1 and V2. What anatomical structures are most likely affected?