This is a single-centre, prospective, observational cohort study focusing on of patients suffering severe aortic valve stenosis (AS) undergoing emergent transcatheter aortic valve implantation (TAVI). AS patients undergoing emergent TAVI always have complicated clinical situations. Therefore, the aims of the study are to collect the incidence and outcomes of emergent TAVI in patients with severe symptomatic AS, to assess the safety and effectiveness of emergency TAVI system for severe AS, and to describe a more practical evidence of emergency TAVI system in severe AS patients.

Inclusion Criteria:

1. Every patient that diagnosed with severe aortic valve stenosis (evaluated by echocardiography: peak transaortic valve blood flow rate ≥4.0m/s, or mean transaortic valve pressure gradient ≥40mmHg (≥5.32kPa), or aortic Valve area <0.8cm2, or AVA<0.5cm2/m2);
2. Every patient that 1) required cardiopulmonary resuscitation due to cardiac arrest, or requiring external chest compressions during surgery (Salvage), 2) or has ongoing, refractory (difficult, complicated, and/or unmanageable) unrelenting cardiac compromise, with or without hemodynamic instability, and not responsive to any form of therapy except cardiac surgery (STS/ACC TVT defined "Urgent Status"), 3) or required urgent procedure during same hospitalization in order to minimize chance of further clinical deterioration (examples include, but are not limited to, worsening, sudden chest pain, heart failure, acute myocardial infarction, anatomy, intra-aortic balloon pump, unstable angina with intravenous nitroglycerin or rest angina) (STS/ACC TVT defined "Urgent Status");
3. Every patient that has been informed of the objectives of the study, agreed to participate, has signed the approved consent form, and was willing to accept all relevant examinations and clinical follow-up.

Exclusion Criteria:

1. Anatomically, the approach or aortic root is not suitable for transcatheter aortic valve implantation (TAVI).
2. Anatomical morphology or vascular diseases affecting the device approach.
3. Left ventricular outflow tract obstruction.
4. Primary dilated cardiomyopathy.
5. The echocardiogram indicates the presence of left ventricular thrombus.
6. Cannot tolerate anticoagulation and antiplatelet therapy.
7. Are allergic or resistant to nickel titanium alloys.
8. Active infective endocarditis, or other active infections affecting the effect of TAVI.
9. Severe disabling Alzheimer's disease.
10. Life expectancy< 6 months.
11. Other conditions (examples include poor compliance of patients and families) considered by the investigator to be inappropriate for participation in this clinical trial.

consecutive patients with severe aortic valve stenosis undergoing emergency transcatheter aortic valve implantation