Safety and Efficacy Study of the Medtronic CoreValve® System in the Treatment of Symptomatic Severe Aortic Stenosis in High Risk and Very High Risk Subjects Who Need Aortic Valve Replacement

Inclusion Criteria: * Extreme Risk Only: Subject must have comorbidities such that one cardiologist and two cardiac surgeons agree that medical factors preclude operation, based on a conclusion that the probability of death or serious morbidity exceeds the probability of meaningful improvement. Specifically, the predicted operative risk of death or serious, irreversible morbidity is ≥ 50% at 30 days. * High Risk Surgical Only: Subject must have comorbidities such that one cardiologist and two cardiac surgeons agree that predicted risk of operative mortality is ≥15% (and predicted operative mortality or serious, irreversible morbidity risk of \< 50%) at 30 days. * Subject has senile degenerative aortic valve stenosis with: mean gradient \> 40 mmHg, or jet velocity greater than 4.0 m/sec by either resting or dobutamine stress echocardiogram, or simultaneous pressure recordings at cardiac catheterization (either resting or dobutamine stress), AND an initial aortic valve area of ≤ 0.8 cm2 (or aortic valve area index ≤ 0.5 cm2/m2) by resting echocardiogram or simultaneous pressure recordings at cardiac catheterization * Subject is symptomatic from his/her aortic valve stenosis, as demonstrated by New York Heart Association (NYHA) Functional Class II or greater. * The subject or the subject's legal representative has been informed of the nature of the trial, agrees to its provisions and has provided written informed consent as approved by the IRB of the respective clinical site. *…