Huge thrombus formation 1 year after percutaneous closure of an atrial septal defect with an Amplatzer septal occluder

The Amplatzer septal occluder (ASO) has become the device of choice for interventional closure of atrial septal defects (ASDs) in many institutions during the last decades. Although excellent results have been reported for the device, concerns have arisen about the long-term complications (1). Of these complications, thrombus formation was rarely seen after 1 year in patients (2–4). This is the first report of a pediatric patient of a huge thrombus developing on an ASO device detected by transthoracic echocardiography on a routine examination after 1 year of implantation without a risk factor.