Medtronic CoreValve Evolut R U.S. Clinical Study (Evolut 34R Addendum)

Inclusion Criteria: 1. Severe aortic stenosis, defined as aortic valve area of \< 1.0 cm2 (or aortic valve area index of \< 0.6 cm2/m2) by the continuity equation, AND mean gradient \> 40 mmHg or maximal aortic valve velocity \> 4.0 m/sec by resting echocardiogram. Subjects with low-flow/low gradient severe aortic stenosis can be included, provided low-dose dobutamine or exercise stress echocardiography demonstrates a mean gradient of \> 40 mmHg or a maximal aortic valve velocity of \> 4.0 m/sec, AND aortic valve area of \< 1.0 cm2 (or aortic valve area index of \< 0.6 cm2/m2). 2. Society of Thoracic Surgeons (STS) score of ≥ 8 OR documented heart team agreement of ≥ high risk for aortic valve replacement due to frailty or co-morbidities. 3. Symptoms of aortic stenosis, AND New York Heart Association (NYHA) Functional Class II or greater. 4. The subject and the treating physician agree that the subject will return for all required post-procedure follow-up visits. Exclusion Criteria: 5. Any condition considered a contraindication for placement of a bioprosthetic valve (e.g. subject is indicated for mechanical prosthetic valve). 6. A known hypersensitivity or contraindication to any of the following which cannot be adequately pre-medicated: * aspirin or heparin (HIT/HITTS) and bivalirudin * ticlopidine and clopidogrel * Nitinol (titanium or nickel) * contrast media 7. Blood dyscrasias as defined: leukopenia (WBC \< 1000 mm3), thrombocytopenia (platelet count \<50,000 cells/mm3), history of bleeding diathesis or coagulopathy, or hypercoagulable states. 8. Untreated clinically significant coronary artery disease requiring revascularization. 9. Severe left ventricular dysfunction with left ventricular ejection fraction (LVEF) \< 20% by echocardiography, contrast ventriculography, or radionuclide ventriculography. 10. End stage renal disease requiring chronic dialysis or creatinine clearance \< 20 cc/min. 11. Ongoing sepsis, including active endocarditis. 12. Any percutaneous coronary or peripheral interventional procedure with a bare metal or drug eluting stent performed within 30 days prior to study procedure. 13. Symptomatic carotid or vertebral artery disease or successful treatment of carotid stenosis within 10 weeks of Heart Team assessment. 14. Cardiogenic shock manifested by low cardiac output, vasopressor dependence, or mechanical hemodynamic support. 15. Recent (within 6 months of Heart Team assessment) cerebrovascular accident (CVA) or transient ischemic attack (TIA). 16. Gastrointestinal (GI) bleeding that would preclude anticoagulation. 17. Subject refuses a blood transfusion. 18. Severe dementia (resulting in either inability to provide informed consent for the study/procedure, prevents independent lifestyle outside of a chronic care facility, or will fundamentally complicate rehabilitation from the procedure or compliance with follow-up visits). 19. Estimated life expectancy of less than 12 months due to associated non-cardiac co-morbid conditions. 20. Other medical, social, or psychological conditions that in the opinion of the investigator precludes the subject from appropriate consent or adherence to the protocol required follow-ups exams. 21. Currently participating in an investigational drug or another device study (excluding registries). 22. Evidence of an acute myocardial infarction ≤ 30 days before the study procedure. 23. Need for emergency surgery for any reason. 24. Liver failure (Child-Pugh class C). 25. Subject is pregnant or breast feeding. Anatomical exclusion criteria: 26. Pre-existing prosthetic heart valve in any position. 27. Mixed aortic valve disease (aortic stenosis with severe aortic regurgitation). 28. Severe mitral regurgitation. 29. Severe tricuspid regurgitation. 30. Moderate or severe mitral stenosis. 31. Hypertrophic obstructive cardiomyopathy. 32. Echocardiographic or Multi-Slice Computed Tomography (MSCT) evidence of intracardiac mass, thrombus, or vegetation. 33. Congenital bicuspid or unicuspid valve verified by echocardiography. For transfemoral or transaxillary (subclavian) access: 34. Access vessel diameter \< 5.5 mm or \<6.0 mm for patent left internal mammary artery (LIMA)