Abstract Background: Aortic valve replacement (AVR) is crucial for patients with severe aortic valve disease. However, managing those with a small aortic annulus (SAA, i.e., annulus diameter < 22 mm) is challenging because implanting a small prosthesis can result in patient-prosthesis mismatch (PPM), suboptimal hemodynamic outcomes, and reduced long-term survival. Traditional surgical techniques for aortic root enlargement (ARE), such as the Nicks and Manougian procedures, have significant limitations, typically allowing enlargement of only one to two prosthesis sizes and involving complex reconstructive procedures. The novel "Y incision" technique by Bo Yang offers a promising alternative, allowing implantation of valves up to five sizes larger than the native annulus, but it lacks comprehensive comparative data on its safety, efficacy, and functional outcomes.

Aim: This study aims to compare the safety outcomes, hemodynamic performance, and functional capacity of the "Y incision" technique versus standard surgical enlargement techniques in patients with a small aortic annulus undergoing AVR, with particular emphasis on objective functional assessment using cardiopulmonary exercise testing (CPET).

Methods: This prospective, randomized, controlled superiority trial will enroll patients with aortic valve disease and a small aortic annulus where conventional AVR is expected to result in moderate or severe PPM. Patients will be randomized 1:1 to either the standard surgical technique group or the "Y incision" technique group. Based on preliminary results and power calculations using the Win Ratio methodology, the sample size is set at 90 patients (45 in each group) to account for potential dropouts.

Primary Endpoint: Hierarchical composite endpoint analyzed using Win Ratio methodology, including (in order of priority): all-cause mortality, stroke, myocardial infarction, total hospitalization rate, moderate or severe PPM, exercise-induced valve dysfunction, and functional improvement at specified time points through 12 months.

Secondary Endpoints: Safety outcomes including intraoperative and 30-day complications, long-term anatomical complications, hemodynamic parameters assessed by echocardiography, functional outcomes measured by 6-minute walk distance and CPET (including peak VO₂), quality of life assessed using KCCQ questionnaire, and prosthetic valve-related outcomes at 3, 6, and 12 months post-surgery.

Conclusion: By providing robust, randomized controlled data with objective functional capacity assessment, this study aims to fill current gaps in knowledge regarding the long-term outcomes, safety profile, and functional benefits of the "Y incision" technique compared to standard surgical methods, potentially establishing evidence-based guidance for managing patients with a small aortic annulus undergoing AVR.

Inclusion Criteria:

• Adults aged 18-80 years.
• Patients must have signed and dated an ICF in accordance with regulatory and institutional guidelines before any protocol-related procedures and must be willing and able to comply with scheduled visits.
• Diagnosed with aortic valve disease requiring aortic valve replacement.
• Patients with small aortic annulus relative to body size where conventional AVR result in moderate or severe PPM (defined as cases where the largest prosthesis that can be implanted in the native annulus would provide a predicted iEOA ≤0.85 cm²/m² for BMI <30, or ≤0.70 cm²/m² for BMI ≥30), based on manufacturer specifications and patient BSA).
• Suitable candidates for surgery as determined by the heart team.

Exclusion Criteria:

1. Patients for whom conventional AVR without root enlargement is not expected to result in patient-prosthesis mismatch.
2. Prior cardiac surgery.
3. Severe concomitant valvular disease requiring additional procedures.
4. Active endocarditis.
5. Severe chronic lung disease
6. Pre-existing lower limb deficits or any other medical comorbidities that interfere significantly with gait or the ability to perform exercise testing on a bicycle ergometer
7. Severe left ventricular dysfunction (LVEF < 30%).
8. Contraindications to surgery.
9. Concurrent active treatment in another clinical trial

Undecided