Investigation of the NVT ALLEGRA Plus THV System in Patients With Severe Aortic Stenosis or Failed Surgical Aortic Bioprosthesis

Inclusion Criteria:

1. Symptomatic severe calcific stenosis of a native aortic valve with an AVA ≤1.0 cm2 (or AVA index ≤0.6 cm2/m2), AND mean aortic pressure gradient ≥ 40mmHg OR maximaltransaortic velocity ≥4.0m/s OR Doppler velocity index ≤0.25 on site-reportedechocardiography OR symptomatic patients with degeneration of a surgicalbioprosthetic valve (stenosis +/- insufficiency) on site-reported echocardiography

2. Local multi-disciplinary Heart Team and Central Screening Committee (CSC) agree onindication and eligibility for TAVI

3. Age ≥18 years

4. Patient has signed the Patient Informed Consent Form

5. Patient is willing and able to comply with requirements of the study, including allfollow-up visits

Exclusion Criteria:

Patient will not be included if ANY one of the following conditions exists:

General:

1. Mean aortic annulus diameter as measured by pre-procedural CT or internal diameterof the bioprosthesis is <16.5 mm or >27 mm

2. Echocardiographic evidence of intracardiac thrombus or vegetation (site-reported)

3. Significant disease of the aorta that would preclude safe advancement of the ALLEGRAPlus THV System

4. Severe ilio-femoral vessel disease that would preclude safe placement of an 18 Frintroducer sheath or make endovascular access impossible

5. Porcelain aorta

6. Severe left ventricular dysfunction with ejection fraction (EF) <20% (site-reported)

7. Evidence of active endocarditis or other acute infections

8. Renal failure requiring continuous renal replacement therapy

9. Untreated clinically significant coronary artery disease requiring revascularization

10. Any percutaneous interventional procedure (e.g. PCI with stenting) within 14 daysprior of the index procedure

11. Acute MI ≤30 days prior to the index procedure

12. Symptomatic carotid or vertebral artery disease requiring intervention orcarotid/vertebral intervention within the preceding 45 days

13. Cerebrovascular accident (CVA) or transient ischemic attack (TIA) ≤6 months or priorCVA with moderate or severe disability (e.g. modified Rankin scale score >2)

14. History of bleeding diathesis or coagulopathy; acute blood dyscrasias as defined:thrombocytopenia (platelets <80,000/µl), acute anemia (hemoglobin <10 g/dl),leukopenia (WBC <3000/ µl)

15. Active peptic ulcer or gastrointestinal (GI) bleeding ≤3 months

16. Severe (greater than 3+) mitral insufficiency (site-reported)

17. Uncontrolled atrial fibrillation

18. Required emergency surgery for any reason

19. Known hypersensitivity to contrast media, which cannot be adequately pre-medicatedor contraindication to anticoagulant or anti-platelet medication or to nitinol alloyor to bovine tissue

20. Life expectancy ≤12 months due to other medical illness

21. Currently participating in another investigational drug or device study

22. Hypertrophic obstructive cardiomyopathy

23. Pregnancy or intend to become pregnant during study participation Specific exclusions in patients with native aortic valve disease (site-reported):

24. Unicuspid or bicuspid aortic valve

25. Non-calcified aortic stenosis

26. Identified risk of coronary occlusion due to Sinus of Valsalva anatomy and/or bulkycalcified aortic valve leaflets in close proximity to coronary ostia Specific exclusions in patients with degenerated surgical bioprosthetic aorticvalves (valve-in-valve) (site-reported):

27. High risk of coronary occlusion

28. Partially detached leaflets that may obstruct a coronary ostium