What is a significant risk associated with an undetected atrial septal defect?

An undetected atrial septal defect (ASD) allows for blood to flow between the left and right atria of the heart. This shunting of blood can lead to a situation where a thrombus (a blood clot) formed in the venous system or right side of the heart may pass into the systemic circulation, resulting in a paradoxical embolism. This occurs because the clot bypasses the usual filtration that would occur in the lungs and can directly enter the arterial system, potentially traveling to the brain or other vital organs, ultimately increasing the risk of stroke.

The relationship between ASD and stroke risk highlights the importance of early detection and management of this condition to prevent serious complications. Though conditions like chronic pulmonary hypertension, heart valve stenosis, and coronary artery disease can arise or be exacerbated by various cardiac anomalies, the specific acute risk of a stroke from paradoxical embolism is a direct consequence of an undetected ASD, making it a significant concern in affected patients.