This study is a prospective observational clinical trial, in which severe AS patients aged 50-70 years with SAA choose modified ARE or TAVR according to their wishes to investigate the safety and efficacy of modified ARE; Compare the incidence and clinical outcomes of moderate to severe PPM after modified ARE and TAVR surgery; Evaluate the feasibility of postoperative mid valve TAVR and explore the most ideal initial surgical plan for this type of patient from a full lifecycle perspective.

Small aortic annulus (SAA), which is prevalently observed in patients with severe aortic stenosis (AS), constitutes a significant challenge in treatment and may give rise to post-operative prosthetic valve mismatch (PPM) and an elevated late mortality rate. The optimal approach for treating SAA remains controversial. Transcatheter aortic valve replacement (TAVR) has yielded superior valvular hemodynamic outcomes in patients with SAA; however, the incidence of PPM subsequent to surgery remains considerable. Aortic root enlargement (ARE) represents an effective solution for SAA, but the conventional method of aortic ring enlargement for ARE has restricted efficacy. In 2021, Yang Bo proposed an enhanced ARE approach, where the mitral curtain of the aortic valve was incised in an inverted Y-shape along the left non-coronary junction, enabling the enlargement of the number 3-5 of the aortic ring

Inclusion Criteria:

• 1) Symptomatic severe AS patients aged 50-70 years who are planning to undergo biological valve replacement (diagnostic criteria for echocardiography are: mean transvalvular pressure gradient ≥ 40mmHg or flow velocity ≥ 4.0 m/s, aortic valve area (AVA) ≤ 0.8 cm2 or iEOA<0.5 cm2/m2) 2) Merge SAA (defined as mean aortic annulus diameter ≤ 23 mm measured by CT)

Exclusion Criteria:

• 1) High surgical risk, STS score>8% 2) Severe lesions in multiple coronary arteries requiring PCI or CABG 3) Simultaneous surgical intervention is required for severe mitral and tricuspid valve disease 4) Combining other complex cardiovascular diseases requires simultaneous surgical treatment 6) Combined severe pulmonary arterial hypertension or left ventricular dysfunction (LVEF<40%) 7) Severe respiratory, liver and kidney dysfunction, or other important organ dysfunction combined 8) Concurrent infective endocarditis in active phase 9) Previous history of cardiac surgery

Severe AS patients aged 50-70 years with SAA can choose modified ARE or TAVR according to their wishes to study the safety and effectiveness of modified ARE; Compare the incidence and clinical outcomes of moderate to severe PPM after modified ARE and TAVR surgery; Evaluate the feasibility of postoperative mid valve TAVR and explore the most ideal initial surgical plan for this type of patient from a full lifecycle perspective.