Target Value Study to Evaluate the Safety and Efficacy of the Taurus NXT® Transcatheter Aortic Valve System for the Treatment of Severe Calcific Aortic Stenosis

Inclusion Criteria: * Patients who voluntarily participate and sign the informed consent form, and are able to comply with the entire trial process. * Age ≥ 70 years. * Severe aortic stenosis (AS): Echocardiography shows a transaortic flow velocity ≥ 4.0 m/s, or a mean transaortic pressure gradient ≥ 40 mmHg (1 mmHg = 0.133 kPa), or an aortic valve area ≤ 1.0 cm², or an effective orifice area index ≤ 0.5 cm²/m²; for patients with low flow/low gradient, severe AS is confirmed by dobutamine stress echocardiography, Doppler ultrasound evaluation, or other imaging modalities. * Symptomatic patients: symptoms such as dyspnea, chest pain, or syncope, with New York Heart Association (NYHA) functional class ≥ II (including class II), and these symptoms are clearly attributable to AS. * Anatomically suitable for transcatheter aortic valve replacement (TAVR): including but not limited to valve calcification degree, aortic annulus diameter, aortic sinus diameter and height, coronary ostium height, and vascular access diameter. * Expected life expectancy \> 12 months after correction of AS. * Assessed by the heart team (including at least two cardiovascular surgeons) as unsuitable for conventional surgical aortic valve replacement. Exclusion Criteria: * Subjects with bacteremia or septicemia. * Active endocarditis. * Any intracardiac mass, left ventricular or atrial thrombus, or vegetation detected on echocardiography. * Severe mitral or tricuspid regurgitation. * Known severe allergic reactions to contrast media, aspirin, heparin, ticlopidine-class drugs, nitinol, or bovine products. * Other serious diseases that may reduce life expectancy to less than 12 months. * Current substance abuse issues (e.g., alcohol, cocaine, heroin, etc.). * Subjects with severe coagulation disorders. * Hemoglobin \< 60 g/L. * Currently undergoing dialysis or baseline creatinine level \> 3.0 mg/dL (266 μmol/L). * Severe left ventricular dysfunction with left ventricular ejection fraction \< 20%. * Stroke occurring within the past 3 months. * Acute myocardial infarction (Q-wave MI or non-Q-wave MI with CK-MB \> 2 times the upper limit of normal and/or elevated troponin) within the past 1 month. * Abdominal or thoracic aortic aneurysm. * Hepatic encephalopathy or acute active hepatitis. * Neurological diseases severely affecting mobility and activities of daily living. * Mental illness or psychological disorder preventing normal expression/communication. * Participation in another drug or medical device clinical trial within 3 months prior to screening. * Other conditions considered by the investigator as unsuitable for participation in this clinical trial.