An Atrial Septal Aneurysm (ASA) describes a specific anatomical variation in the heart’s structure. When a physician uses the term “aneurysmal,” they are referring to a section of the heart wall that is unusually floppy or redundant. This condition is often discovered incidentally during routine heart imaging tests. While the presence of an ASA requires careful evaluation, for many people, it does not cause immediate symptoms or require invasive treatment.
Defining Atrial Septal Aneurysm and Cardiac Anatomy
The heart is divided into four chambers, with the two upper chambers, the atria, separated by the atrial septum. This septum keeps deoxygenated blood in the right atrium separate from oxygenated blood returning to the left atrium. An Atrial Septal Aneurysm is not a weakening of a blood vessel wall, as with typical aneurysms, but rather an excessive amount of tissue in this dividing wall.
The term “aneurysmal” means the septal tissue is thin and hypermobile, causing it to bulge out like a wind-filled sail. This bulging can extend into the right atrium, the left atrium, or oscillate back and forth between both chambers during the cardiac cycle. Medically, the septum is classified as aneurysmal if the tissue excursion, or movement, is at least 10 millimeters beyond the plane of the septum, or 15 millimeters total between the atria.
The ASA is a congenital anatomical variation, meaning it is present from birth, though its exact cause is often unknown. The ASA usually affects the area of the septum known as the fossa ovalis, which is the remnant of a fetal opening. This structural anomaly is relatively common, estimated to be found in approximately 1% to 2.5% of the adult population. The significance of the ASA often relates to its frequent association with other interatrial communications.
Diagnostic Methods Used for Identification
The discovery of an Atrial Septal Aneurysm relies on non-invasive cardiac imaging techniques, primarily echocardiography, which visualizes the heart’s structure and function. A Transthoracic Echocardiogram (TTE) is the initial diagnostic step, using ultrasound through the chest wall to image the heart.
Clinicians look for the characteristic bulging or excessive mobility of the atrial septum. The TTE measures the extent of septal excursion to confirm the diagnosis based on established millimeter criteria.
If the initial TTE suggests an ASA or if a patient has experienced an unexplained stroke, a Transesophageal Echocardiogram (TEE) is often performed. The TEE provides superior clarity because the transducer is passed down the esophagus, placing it directly behind the heart without interference from the ribs or lungs. This detailed view is particularly useful for assessing the full anatomy of the atrial septum and for detecting small associated defects. The TEE also allows for specialized testing, such as a bubble study, to confirm if there is any communication between the two upper chambers.
Clinical Significance and Association with Stroke Risk
The main reason an Atrial Septal Aneurysm is clinically significant is its strong association with a condition called Patent Foramen Ovale (PFO). A PFO is a small flap-like opening in the atrial septum that failed to close completely after birth. The redundant tissue of the ASA is often found adjacent to this opening, and the two conditions frequently coexist.
The presence of both an ASA and a PFO together is considered a high-risk anatomical combination for cryptogenic stroke. This elevated risk is attributed to the mechanism of paradoxical embolism. In this scenario, a blood clot originating from the venous system, such as a deep vein thrombosis in the legs, travels to the right side of the heart.
Normally, the clot would be filtered by the lungs. However, the PFO acts as a direct conduit, allowing the clot to pass from the right atrium to the left atrium. This passage is often facilitated when pressure in the right atrium transiently increases, such as during a cough or strain. Once the clot enters the left atrium, it moves into the systemic arterial circulation and can travel to the brain, causing an ischemic stroke or a transient ischemic attack (TIA). The mobile tissue of the ASA may further facilitate the clot’s passage or serve as a site for small clots to form.
Long-Term Monitoring and Management Strategies
For an asymptomatic patient whose Atrial Septal Aneurysm is discovered incidentally, the standard approach is conservative management involving periodic clinical surveillance. No intervention is required for an isolated ASA without associated symptoms or a history of embolic events. Monitoring may include repeat echocardiograms to check for structural changes or the development of associated complications.
If a patient has experienced a cryptogenic stroke or TIA, and the ASA (often paired with a PFO) is identified as the likely cause, management focuses on preventing recurrence. Risk stratification tools, such as the Risk of Paradoxical Embolism (RoPE) score, are used to estimate the probability that the ASA/PFO was the source of the stroke.
Medical management includes antiplatelet medications, such as aspirin, to reduce the blood’s ability to clot. In high-risk situations or if the patient has other indications like atrial fibrillation, anticoagulation therapy may be prescribed. For younger patients (generally under 60) with a high-risk ASA and PFO who have experienced a cryptogenic stroke, procedural closure of the PFO may be recommended. Clinical trials have demonstrated that transcatheter device closure, where a small device is implanted to permanently seal the opening, is superior to antiplatelet therapy alone in reducing the rate of recurrent stroke in this specific patient group.