Arcevo LSA for Aortic Arch Aneurysms and Dissections Safety and Effectiveness Study

General Inclusion Criteria 1. ≥18 years of age or ≤80 years of age (male or female) at time of surgery 2. 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 3. Patient, or patient's legally authorized representative (LAR; in the secondary arm only), provides written informed consent prior to any study procedures 4. Patient's surgery occurs within 90 days of informed consent Anatomical Inclusion Criteria 5. Aortic diameter at the intended Arcevo™ LSA anastomosis site is ≥ 21 mm 6. For Aneurysm with distal sealing (i.e., single stage procedure), aortic diameter at the intended distal sealing zone is between 20-36 mm 7. For Dissection with distal sealing, aortic diameter at the intended distal sealing zone is between 22-40 mm 8. LSA branch does not require additional stenting further into the LSA (beyond the Arcevo™ LSA) 9. The intended LSA sealing zone has a diameter between 8.5 mm and 14.0 mm with a length of at least 10 mm 10. Absence of dissection, aneurysm, or stenosis in the intended LSA sealing zone 11. The intended LSA branch position does not interrupt flow to any branch vessel (e.g., left vertebral artery) 12. Patient does not have computed tomography (CT) evidence of extreme arch or LSA angulation precluding safe passage of the Arcevo™ LSA and delivery system 13. LSA take-off angle between 15° and 90° 14. For patients requiring planned extension, there is a ≥ 2 cm distal seal zone for the TEVAR device without a severely angulated descending aorta 15. For patients requiring planned extension, patient has suitable iliac artery anatomy for safe passage of the TEVAR delivery system General Exclusion Criteria 1. Patient is pregnant, or planning to become pregnant during the course of the study; individuals of child-bearing potential must agree to use acceptable methods of contraception during the study 2. Patient has another medical condition (aside from the arch disease) that, in the opinion of the investigator, reduces the patient's life expectancy to \< 2 years 3. Patient has an existing aortic stent graft device in the descending aorta that would interact with Arcevo™ LSA 4. Patient has a medical, social, or psychological problem that, in the opinion of the investigator, could impede the patient's ability to return for follow-up 5. Patient is unwilling or unable to comply with the follow-up schedule 6. Patient is institutionalized due to administrative or judicial order 7. Patient is unwilling to accept blood transfusion or blood product 8. Patient is currently participating in another interventional clinical study which includes treatment with another investigational product (e.g., device, pharmaceutical or biologic) Medical Exclusion Criteria 9. Patient is unfit for open surgical repair involving circulatory arrest 10. Patient is in extreme hemodynamic compromise requiring cardiopulmonary resuscitation (CPR) or substantial inotropic support prior to surgery 11. Patient has an active systemic infection 12. Patient has endocarditis or active infection of the aorta 13. Patient has a freely ruptured aorta 14. Patient has a history of a bleeding disorder (e.g., hemophilia) 15. Patient has current end-stage renal disease (e.g., GFR \<30 mL/min) 16. Patient has a known allergy to Arcevo™ LSA components and TEVAR device components (if required) (nitinol, polyester, platinum-iridium, or polyethylene) 17. Patient has uncontrollable anaphylaxis to iodinated contrast or other inability to obtain CT angiograms during follow-up 18. Patient has acute coronary malperfusion 19. Patient has symptomatic visceral malperfusion