Cardiovascular disease remains a major threat to global health, and structural heart disease which encompassing congenital heart defects, valvular disease, and cardiomyopathies constitutes a substantial proportion of its burden. Atrial septal defect (ASD) is among the most common congenital heart conditions, occurring in approximately 1.6 per 1,000 live births. Percutaneous closure of ASD has become the standard treatment due to its minimally invasive nature and proven efficacy. However, conventional closure procedures rely heavily on fluoroscopic guidance and iodinated contrast, which carry risks of radiation exposure, contrast-related harm, and limit applicability in specific patient groups. Moreover, such procedures must be performed in catheterization laboratories equipped with digital subtraction angiography systems.

To overcome these limitations, our team has spent over a decade developing a fully ultrasound-guided, radiation-free, contrast-free percutaneous intervention system-an original Chinese innovation that has pioneered "no incision, no fluoroscopy, and no general anesthesia" treatment for structural heart disease. This methodology has evolved into a comprehensive technical system and has been successfully applied to ASD, PFO, ventricular septal defect (VSD), patent ductus arteriosus (PDA), and several valvular disorders. It has been recognized by national clinical guidelines (2017), awarded the Chinese Medical Association First-Class Science and Technology Award (2022), and honored by the World Health Organization Innovation Award.

Building upon the unique advantages of ultrasound-only guidance, we further developed a Mobile Surgical Vehicle. This mobile surgical unit integrates ultrasound imaging, sterilization, monitoring, and anesthesia equipment, enabling true "hospital-free" procedures for underserved regions lacking large medical devices. Early applications in remote areas of Southwest China and Belt-and-Road countries have demonstrated promising safety and feasibility.

Nevertheless, high-quality clinical evidence evaluating this mobile platform for ASD closure is lacking. To address this gap, we propose a multicenter randomized controlled trial to demonstrate that mobile-platform ultrasound-guided closure is non-inferior to conventional in-hospital ultrasound-guided procedures. This study will also refine methodology, workflow, and safety protocols for mobile interventional therapy. Its findings will provide essential evidence supporting this original Chinese technology, expand its international impact, and enable broader access for patients in remote regions.

Inclusion Criteria:

• Patients ≥8 years and able to undergo percutaneous intervention under local anesthesia.
• Diagnosed with secundum ASD with a defect diameter of ≥6 mm and ≤36 mm, accompanied by right-sided volume overload.
• Anatomical features suitable for transcatheter closure: the distance from the defect rim to the coronary sinus, superior vena cava, inferior vena cava, and pulmonary veins is ≥5 mm; and the distance to the mitral valves is ≥7 mm.

Exclusion Criteria:

• Presence of primum ASD or sinus venosus ASD.
• Infective endocarditis or intracardiac thrombus.
• ASD with right-to-left shunting.
• Concomitant intracardiac anomalies requiring simultaneous surgical repair.