• ≥18 years of age or ≤80 years of age (male or female) at time of surgery

• Patient has one of the following indications for open surgery based on computed tomography angiography (CTA) completed within 90 days of informed consent:

‣ Acute, subacute, or chronic dissection that involves the aortic arch and the descending thoracic aorta, with or without involvement of the ascending aorta

⁃ Aneurysm that involves the aortic arch and the descending thoracic aorta, with or without involvement of the ascending aorta

• Patient, or patient's legally authorized representative (LAR; in the secondary arm only), provides written informed consent prior to any study procedures

• Patient's surgery occurs within 90 days of informed consent

• Anatomical Inclusion Criteria

• Aortic diameter at the intended Arcevo™ LSA anastomosis site is ≥ 21 mm

• For Aneurysm with distal sealing (i.e., single stage procedure), aortic diameter at the intended distal sealing zone is between 20-36 mm

• For Dissection with distal sealing, aortic diameter at the intended distal sealing zone is between 22-40 mm

• LSA branch does not require additional stenting further into the LSA (beyond the Arcevo™ LSA)

• The intended LSA sealing zone has a diameter between 8.5 mm and 14.0 mm with a length of at least 10 mm

⁃ Absence of dissection, aneurysm, or stenosis in the intended LSA sealing zone

⁃ The intended LSA branch position does not interrupt flow to any branch vessel (e.g., left vertebral artery)

⁃ Patient does not have computed tomography (CT) evidence of extreme arch or LSA angulation precluding safe passage of the Arcevo™ LSA and delivery system

⁃ LSA take-off angle between 15° and 90°

⁃ For patients requiring planned extension, there is a ≥ 2 cm distal seal zone for the TEVAR device without a severely angulated descending aorta

⁃ For patients requiring planned extension, patient has suitable iliac artery anatomy for safe passage of the TEVAR delivery system