The purpose of this study is to evaluate the use of an investigational device called the ValiantTM Visceral Manifold Thoracoabdominal Stent Graft System for the repair of thoracoabdominal aortic aneurysms (TAAA), which is a balloon-like bulge in the aorta (major artery leading away from your heart) that originates in your chest and extends to your abdomen and also includes the branch arteries that supply blood to the liver, spleen, intestine, kidneys and other organs in your abdomen. The word "investigational" means the device is still being tested and is not approved by the Food and Drug Administration (FDA) for sale in the United States.

The primary objective of the clinical investigation is to assess the use of the thoracic bifurcation and the visceral manifold to repair thoracoabdominal aortic aneurysms in patients having appropriate anatomy. The primary intent of the study is to assess safety (i.e. freedom from major adverse events (MAE) at 30 days) and preliminary effectiveness (i.e., treatment success and technical success) of the device (i.e., the proportion of treatment group subjects that achieve and maintain treatment success at one year). Additionally, the study will assess technical success and treatment success at each follow-up interval.

Primary Arm Inclusion Criteria:

A patient may be entered into the study if the patient has at least one of the following

• An aneurysm with a maximum diameter of > 5.5 cm or 2 times the normal diameter just proximal to the aneurysm using orthogonal (i.e., perpendicular to the centerline) measurements
• Aneurysm with a history of growth > 0.5 cm in 6 months
• Saccular aneurysm deemed at significant risk for rupture
• Symptomatic aneurysm greater than or equal to 4.5 cm

Additional Primary Arm Inclusion Criteria:

• Axillary or brachial and iliac or femoral access vessel morphology that is compatible with vascular access techniques, devices or accessories, with or without use of a surgical conduit
• Proximal landing zone for the thoracic bifurcation stent graft that has: (a) ≥ 2.5 cm of nonaneurysmal aortic segment including previously placed graft material (neck) distal to the left subclavian artery (LSA); (b) Diameter in the range of 26-42 mm; (c) Adequate distance from the celiac artery, in order to accommodate cannulation from the antegrade access point when considering the total deployed length of the thoracic bifurcation and visceral manifold
• Iliac artery or aortic distal fixation site, including both native tissue and previously placed graft, greater than or equal to 15 mm in length and diameter in the range of 8 - 25 mm
• Life expectancy: > 1 year

Expanded Use Arm Inclusion Criteria:

• Branch vessel diameter <5mm
• Urgent or emergent presentation
• Patient has a contained rupture
• Patient has a ruptured aneurysm
• Patient has a type B dissection (subacute or chronic) in the portion of the aorta intended to be treated
• Poor performance status including two major system failures (cardiovascular, pulmonary, renal, hepatobiliary, and neuromuscular)
• Baseline creatinine greater than 2.0 mg/dL
• Anatomy that does not allow maintenance of at least one hypogastric artery
• Anatomy that does not allow primary or assisted patency of the left subclavian artery
• Prior aneurysm repair that would involve relining of the previously placed graft material requiring placement of the investigational system in a landing zone that expands beyond any limits of the previously placed graft material
• Obstructive stenting of any or all of the visceral vessels
• Treatment of the patient population listed above will be considered for this expanded arm of the study if they are not a candidate for open surgical repair, cannot be treated with approved devices, and do not meet inclusion into the primary study arm as per opinion of the Principal Investigator, with the concurrence of the IRB.

Primary Arm Exclusion Criteria:

• Patient is a good candidate for and elects for open surgical repair
• Can be treated in accordance with the instructions for use with a legally marketed endovascular prosthesis
• Is eligible for enrollment in a manufacturer- sponsored IDE at the investigational site
• Unwilling to comply with the follow-up schedule
• Inability or refusal to give informed consent by patient or legal representative
• Urgent or emergent presentation
• Patient is pregnant or breastfeeding
• Patient has a contained rupture
• Patient has a ruptured aneurysm
• Patient has a dissection in the portion of the aorta intended to be treated
• Obstructive stenting of any or all of the visceral vessels
• Poor performance status including two major system failures (cardiovascular, pulmonary, renal, hepatobiliary, and neuromuscular)
• Prior aneurysm repair that would involve relining of the previously placed graft material requiring placement of the investigational system in a landing zone that expands beyond any limits of the previously placed graft material
• Known sensitivities or allergies to the materials of construction of the devices, including nitinol (Nickel: Titanium), polyester, platinum-iridium, polytetrafluoroethylene (PTFE), platinum, gold, polyethylene, or stainless steel.
• Known hypersensitivity or contraindication to anticoagulation or contrast media that cannot be adequately medically managed
• Uncorrectable coagulopathy
• Body habitus that would inhibit x-ray visualization of the aorta or exceeds the safe capacity of the equipment
• Patient has had a major surgical or interventional procedure unrelated to the treatment of the aneurysm planned < 30 days of the endovascular repair
• Unstable angina (defined as angina with a progressive increase in symptoms, new onset at rest or nocturnal angina)
• Systemic or local infection that may increase the risk of endovascular graft infection
• Baseline creatinine greater than 2.0 mg/dL
• History of connective tissue disorders (e.g., Marfan Syndrome, Ehler's Danlos Syndrome)
• ranch vessel diameter less than 5 mm
• Thrombus or excessive calcification within the neck of the aneurysm
• Anatomy that would not allow maintenance of at least one patent hypogastric artery
• Anatomy that would not allow primary or assisted patency of the left subclavian artery

5 years

Assessed via physical examination, blood samples, metabolic panel, and other tests at follow-up visits.