The heart has four chambers, with the atrial septum dividing the upper two (atria) to keep oxygen-rich and oxygen-poor blood separate. An aneurysm is a localized bulging of an organ wall. An aneurysmal atrial septum (ASA) is a structural variation where this dividing wall bulges abnormally, typically present from birth.
Understanding the Atrial Septum and its Aneurysm
An aneurysmal atrial septum (ASA) involves a section of the septum, often near the fossa ovalis, exhibiting excessive mobility and protrusion. This structural variation is distinct from a hole in the septum, though it can be associated with one.
Diagnosis typically occurs when the septal tissue protrudes more than 10 millimeters, sometimes up to 15 millimeters, beyond the normal plane of the atrial wall. This bulging can extend into either the left or right atrium, or both, and its appearance may vary during the heart’s pumping and relaxing cycles.
Clinical Significance and Associated Conditions
Many individuals with an aneurysmal atrial septum experience no symptoms, and the condition is often discovered incidentally during a heart examination for other reasons. However, an aneurysmal atrial septum can be associated with other cardiac conditions, most notably a patent foramen ovale (PFO). A PFO is a small opening in the atrial septum that typically closes shortly after birth but remains open in about a quarter of the general population.
The presence of an aneurysmal atrial septum can increase the functional significance of a PFO. The bulging nature of the aneurysm may act as a funnel, potentially enhancing the passage of blood or clots from the right to the left side of the heart. This phenomenon, where a clot originating in the venous system (e.g., from a leg vein) bypasses the lungs and travels to the arterial circulation, is known as a paradoxical embolism. Such an event can lead to complications like a stroke or a transient ischemic attack (TIA), particularly in younger individuals where other causes of stroke are less common.
Research indicates that an aneurysmal atrial septum, especially when combined with a PFO, is associated with cryptogenic stroke, which is a stroke of unknown cause. Studies suggest that an aneurysmal atrial septum is a more important predictor of recurrent stroke than the size of the PFO itself. Specifically, an atrial septal aneurysm with an excursion greater than 10 millimeters has been linked to an approximately eight times higher risk of stroke compared to smaller aneurysms. While this association exists, many people with both an aneurysmal atrial septum and a PFO will never experience these complications.
Diagnosis and Management
An aneurysmal atrial septum is primarily diagnosed through imaging techniques, with echocardiography being the most common method. A transthoracic echocardiogram (TTE), which involves placing a device on the chest, is often the initial test. However, a transesophageal echocardiogram (TEE) provides a clearer and more detailed view of the atrial septum, often detecting aneurysms that a TTE might miss. During these tests, medical professionals look for the characteristic bulging and measure the extent of its protrusion. If a PFO is suspected, a “bubble study” involving agitated saline can be performed to visualize blood shunting across the septum.
Management of an aneurysmal atrial septum often involves observation and regular monitoring, especially if no symptoms are present or if it is an isolated finding. Doctors may recommend follow-up echocardiograms every one to two years to monitor for any changes. If there is a history of stroke or TIA, or if other risk factors for blood clots are present, medication such as antiplatelet drugs (e.g., aspirin) or anticoagulants might be prescribed to reduce the risk of future embolic events.
For select high-risk patients, particularly those who have experienced a cryptogenic stroke in conjunction with an aneurysmal atrial septum and PFO, a minimally invasive procedure to close the PFO may be considered. This decision is highly individualized, taking into account the patient’s symptoms, overall health, and specific risk factors. Surgical intervention to remove the aneurysmal atrial septum is rare and typically reserved for specific, complex situations.