A prospective, multicenter, randomized controlled, non-inferiority clinical trial to evaluate the safety and efficacy of the AbsnowTM II absorbable atrial septal defect occluder system for atrial septal defect closure therapy. A parallel controlled comparison will be conducted using the Cera atrial septal defect occluder manufactured by the same company as the control device, to evaluate the safety and efficacy of the AbsnowTM II absorbable ASD occluder system in the treatment of ASD occlusion.

This study is expected to be conducted at multiple centers, adopting a prospective, multicenter, randomized controlled, non-inferiority design, and is divided into the following two phases:

• Roll-in Phase: Each study center may enroll 1 to 3 roll-in subjects. Investigators will implant the absorbable atrial septal defect occluder system to gain procedural familiarity with the investigational device. (Roll-in subjects will not be included in the confirmatory trial statistical analysis.)
• Confirmatory Trial: A prospective, multicenter, randomized controlled, non-inferiority trial design will be adopted. A total of 236 eligible subjects are planned for enrollment. Qualified subjects will be randomly assigned in a 1:1 ratio to either the test group or the control group. Subjects in the test group will receive treatment with the absorbable atrial septal defect occluder system manufactured by Lifetech Scientific (Shenzhen) Co., Ltd. Subjects in the control group will receive treatment with the Cera atrial septal defect occluder manufactured by the same company.

All subjects will undergo assessments at screening, pre-discharge, and follow-up visits at 1 month, 3 months, 6 months, and 12 months post-procedure. A clinical summary will be prepared after completion of all 12-month follow-up evaluations to support product registration application. After trial completion, all subjects will be followed long-term for 2 to 5 years to evaluate the long-term safety of the device.

Inclusion Criteria:

1. Aged≥3years, body weight≥10 kg, regardless of gender;
2. Patients with secundum atrial septal defect (ASD) with left-to-right shunt and evidence of right ventricular volume overload (echocardiography indicating right ventricular enlargement);
3. ASD diameter≥5 mm and<26 mm;
4. The distance from the ASD rim to the openings of the superior/inferior vena cava and pulmonary veins≥5mm, and the distance to the atrioventricular valve≥7mm;
5. Patients who can understand the trial purpose, voluntarily participate and sign the informed consent form, and are willing to cooperate with follow-up completion.

Exclusion Criteria:

1. Primum, sinus venosus, and unroofed coronary sinus types of atrial septal defect (ASD);
2. Patients with ASD diameter≥26 mm;
3. Combined with other structural heart diseases requiring treatment besides ASD;
4. Complicated with severe pulmonary hypertension or Eisenmenger syndrome;
5. Patients who suffered from infectious diseases within 1 month before enrollment, including infective endocarditis, or those with uncontrolled infectious diseases;
6. Patients who suffered from hemolysis, hemorrhagic diseases, unhealed peptic ulcer within 1 month before enrollment, or have any contraindications to aspirin therapy (except those who can take other antiplatelet drugs continuously for 6 months);
7. Intracardiac thrombus detected by echocardiography (especially thrombus in the left atrium or left atrial appendage), or venous thrombosis at the catheter insertion site;
8. Patients allergic to the materials of the investigational medical device;
9. Pregnant or lactating females, or those who plan to have children during the trial and are unwilling to adopt effective contraceptive measures;
10. Patients who participated in other drug or medical device clinical trials before enrollment and have not reached the primary endpoint;
11. Patients with other factors deemed inappropriate to participate in this clinical trial by the investigator.