Study to Evaluate the Clinical Performance of the Valiant Thoracic Stent Graft With the Captivia Delivery System (Valiant Captivia) for the Treatment of Acute, Complicated Type B Aortic Dissections

Inclusion Criteria * Subject signed an informed consent. * Subject is at least 18 years old. * Subject has an acute, complicated Type B aortic dissection with evidence of at least one of the following: * Malperfusion (visceral, renal, spinal cord and/or lower limb ischemia) * Visceral ischemia measured by either radiographic or clinical evidence. * Renal ischemia measured by either radiographic or clinical evidence. * Spinal cord ischemia measured by either radiographic or clinical evidence. * Lower limb ischemia measured by either radiographic or clinical evidence. * Rupture - Measured by radiographic or clinical evidence. * Subject is hemodynamically stable. * Subject's anatomy must meet all of the following anatomical criteria: Proximal landing zone aortic diameter must be between 20 mm and 44 mm; * Centerline distance from distal margin of left CCA or in cases of bovine anatomy, innominate artery, to start of most proximal tear must be ≥ 20 mm; * Subject has patent iliac or femoral arteries or can tolerate an iliac conduit that allows endovascular access to the dissection site with the delivery system of the appropriate sized device. * Thoracic aortic dissection is confirmed, at a minimum, by diagnostic contrast-enhanced computerized tomography angiogram (CTA) with 3-D reconstruction, and/or contrast enhanced magnetic resonance angiogram (MRA) obtained prior to the implant procedure. Exclusion Criteria * Planned placement of the COVERED portion of the stent graft over the left carotid artery, or the celiac trunk. * Subject has systemic infection. * Subject is pregnant. * Subject has received a previous stent or stent graft or previous surgical repair in the DTA. * Subject has had a cerebral vascular accident (CVA) within 2 months. * Subject has a history of bleeding diathesis, coagulopathy, or refuses blood transfusion. * Subject has a history of Marfan Syndrome or other connective tissue disorder. * Subject is currently participating in an investigational drug or device clinical trial which would interfere with the endpoints and follow-ups of this study. * Subject has a known allergy or intolerance to the device components. * Subject has a known hypersensitivity or contraindication to anticoagulants or contrast media, which is not amenable to pre-treatment. * Subject has a co-morbidity causing expected survival to be less than 1 year.