Normal Axial CT Chest Aortic Arch

A 45-year-old man with uncontrolled hypertension presents with sudden-onset severe tearing chest pain radiating to the back. CT angiography of the chest at the level of the aortic arch is performed. The structures marked **C** (brachiocephalic vessels) are noted to be patent and normally positioned. However, the radiologist observes an intimal flap within the aortic arch with differential flow in the true and false lumens. Which of the following vascular branches arising from the aortic arch is most critical to assess for involvement in determining the classification and surgical urgency of this aortic pathology?