Portico Next Generation Approval Study

The purpose of this clinical study is to evaluate the acute safety and effectiveness of the next-generation Navitor (Portico™ NG) Transcatheter Aortic Heart Valve as assessed by the rate of all-cause mortality at 30 days and the rate of moderate or greater paravalvular leak at 30 days in a high or extreme surgical risk patient population to support CE (Conformité Européenne) Mark and FDA approval.

Key Inclusion Criteria: 1. Subjects must have a Society of Thoracic Surgeons (STS) score of ≥7% OR documented heart team agreement of high or extreme risk for surgical aortic valve replacement due to frailty or co-morbidities not captured by the STS score. 2. Subject has symptomatic aortic stenosis as demonstrated by NYHA (New York Heart Association) Functional Classification of II, III, or IV. 3. Subject has senile degenerative aortic valve stenosis with echo-derived criteria, defined as: aortic valve area (AVA) of ≤ 1.0 cm2 (or indexed EOA (effective orifice area) ≤ 0.6 cm2/m2) AND mean gradient ≥40 mmHg or peak jet velocity ≥ 4.0 m/s or doppler velocity index (DVI) ≤0.25. (Qualifying AVA baseline measurement must be within 90 days prior to informed consent). 4. Aortic annulus diameter of 19-30mm and ascending aorta diameter for the specified valve size listed in the IFU (Instructions For Use), as measured by CT (Computed Tomography) Key Exclusion Criteria: 1. Evidence of an acute myocardial infarction (defined as: ST Segment Elevation as evidenced on 12 Lead ECG) within 30 days prior to index procedure. 2. Any percutaneous coronary or peripheral interventional procedure performed within 30 days prior to index procedure. 3. Blood dyscrasias as defined: leukopenia (WBC\