Early Feasibility Study of the RelayBranch Thoracic Stent-Graft System

Inclusion Criteria: * Age ≥18 years * Anatomy that would require coverage of the brachiocephalic trunk (BCT) and/or left carotid arteries if a non-branch endograft were implanted * At least one of the following: a. Aneurysm of the ascending aorta, aortic arch, or proximal descending aorta that meets at least one of the following: i. ≥ 5.5 cm in diameter ii. ≥ 4.0 cm in diameter that has increased in size by 0.5 cm in the last 6 months iii. Measures twice the size of the normal aorta diameter iv. Is saccular in configuration b. PAU within the ascending aorta, aortic arch, or proximal descending thoracic aorta (DTA) with or without intramural hematoma (IMH) c. Chronic, uncomplicated aortic dissection distal to the BCT (type B), with either aortic diameter ≥5.5 cm or ≥4.0 cm with an increase in size by 0.5 cm in the last 6 months d. IMH distal to the BCT with recurrent symptoms, i.e. hypertension or intractable pain, despite best medical therapy. * A non-aneurysmal proximal aortic neck diameter ranging between 28 mm and 43 mm and a non-aneurysmal distal aortic neck diameter ranging between 19 mm and 43 mm. * A proximal attachment zone of the arch graft, meeting the oversizing requirement, must be a minimum of 25mm in length when measured on the inner curve of the ascending aorta, proximal to the BCT. * Total length from the coronaries to the proximal edge of the BCT must be a minimum of 70mm. * The length of the distal landing zone should be 20mm minimum. * Coverage of the left subclavian artery is permitted. Revascularization of the left subclavian artery may be considered in all cases by the treating physician and, especially, in anatomies where revascularization is determined to be clinically necessary * The distal landing zone must contain a straight segment (non-tapered, non-reverse tapered; defined by \< 10% diameter change) with length equal to or greater than the required attachment length of the intended device * Non-aneurysmal BCT and left common carotid arteries with diameters ranging \> 6.0mm across the entire length of the treatment zone. * Distal branch landing zone must be \<20.0 mm in diameter and a minimum of 25.0 mm in length. * Adequate arterial access for introduction and delivery of the Relay Branch System. Note: Alternative methods to gain proper access can be utilized (e.g., iliac conduit) * Considered high risk or prohibitive risk for conventional surgery by treating physician or aortic team * Must be willing to comply with the follow-up evaluation schedule * Subject or legally authorized representative must sign the informed consent form prior to implant. Exclusion Criteria: * Significant stenosis, calcification, thrombus, or tortuosity of intended fixation sites that would compromise fixation or seal of the device * Aortic angulations (radius) less than 15mm at intended proximal landing zone. * Ascending aortas that would require the arch graft to be deployed less than 15mm distal to the coronaries * Pre-procedure occlusion or planned coverage of both subclavian arteries * Anatomic variants which would compromise circulation to both vertebral arteries after placement of the stent-graft * Prior endovascular repair in the ascending/descending thoracic aorta or aortic arch. The device may not be placed within any prior endovascular graft * Concomitant aneurysm/disease of the abdominal aorta requiring repair * Prior abdominal aortic aneurysm repair (endovascular or surgical) that was performed less than 6 months prior to the planned stent implant procedure * Prior mechanical aortic valve replacement except for hybrid valves with biological leaflets. * Major surgical or medical procedure within 45 days prior to the planned procedure or is scheduled for a major surgical or medical procedure within 60 days post implantation. Except for any planned procedures for the prospective stent-graft placement, e.g., left subclavian artery bypass or transposition * Untreatable allergy or sensitivity to contrast media or device components * Blood coagulation disorder or bleeding diathesis in which the treatment cannot be suspended for one week pre and post repair * Acute Coronary Syndrome (ACS) including unstable angina * Severe Congestive Heart Failure (New York Heart Association functional class IV) * Stroke within 12 months of the planned treatment date * Myocardial infarction within 3 months of the planned treatment date. * Chronic atrial fibrillation or other hypercoagulable condition that requires treatment with anticoagulants or presence of left atrial appendage thrombus * Severe pulmonary disease (documented FEVI \<30% or as assessed by the study physician) at screening * Acute renal failure (defined as serum creatinine \> 2.5mg/dL Note: Patients that have chronic renal failure and are managed medically or through hemodialysis, and can tolerate the follow-up imaging schedule can be included. * Significant carotid bifurcation disease (\>70% diameter reduction by duplex ultrasound or angiography) * Hemodynamic instability * Active systemic infection at the time of treatment * Morbid obesity or other condition that may compromise or prevent the necessary imaging requirements * Connective tissue disorders, mycotic aneurysms, or infected aorta * Less than two-year life expectancy * Current or planned participation in an investigational drug or device study that has not completed primary endpoint evaluation * Currently pregnant or planning to become pregnant during the course of the study * Medical, social, or psychological issues that the Investigator believes may interfere with treatment or follow-up