Hypermobile Interatrial Septum: Clinical Significance and Implications
A hypermobile interatrial septum refers to excessive movement or mobility of the tissue between the right and left atria during the cardiac cycle, which can be a precursor to or associated with atrial septal aneurysm and may increase the risk of paradoxical embolism and atrial arrhythmias.
Definition and Characteristics
Hypermobility of the interatrial septum is characterized by:
- Excessive movement of the interatrial septal tissue during the cardiac cycle
- Movement that exceeds normal physiological motion but may not yet meet criteria for a full atrial septal aneurysm
- May progress to an atrial septal aneurysm, which is defined as abnormally large and redundant septum primum with aneurysmal protrusion into one or both atria 1
- Specifically, an atrial septal aneurysm is defined as having more than 10-mm excursion from the centerline during the cardiac cycle 1
Clinical Significance
Hypermobility of the interatrial septum has several important clinical implications:
Association with Structural Abnormalities
- Often associated with patent foramen ovale (PFO) 1
- May coexist with small atrial septal defects (ASDs) 2
- Can be part of a spectrum of interatrial septal abnormalities that include PFO, ASD, and atrial septal aneurysm
Relationship with Arrhythmias
- Associated with increased risk of atrial arrhythmias, particularly atrial fibrillation 2, 3
- Studies have found a high incidence (43%) of interatrial septal abnormalities, including hypermobility, in patients undergoing ablation for atrial fibrillation 2
- May contribute to arrhythmogenesis by creating electrophysiological substrate for re-entry circuits 3
Thromboembolic Risk
- Increases risk of paradoxical embolism, where thrombi can cross from the venous to arterial circulation 1
- May be a risk factor for cryptogenic stroke, particularly in younger patients 1
Diagnostic Evaluation
Hypermobility of the interatrial septum is typically diagnosed through:
- Echocardiography (transthoracic or transesophageal)
- Transesophageal echocardiography (TEE) is particularly valuable for detailed assessment of interatrial septal morphology 2
- May be incidentally discovered during cardiac imaging for other indications
Clinical Management
Management depends on associated findings and clinical presentation:
- Isolated hypermobility without symptoms: Generally requires monitoring but not specific intervention
- Associated with PFO and history of cryptogenic stroke: May warrant consideration of PFO closure 1
- Associated with atrial fibrillation: May influence ablation strategy and potentially predict lower success rates of catheter ablation 3
- Associated with hemodynamically significant ASD: May require ASD closure (surgical or transcatheter) 1
Important Considerations
Hypermobile interatrial septum should be distinguished from other interatrial septal abnormalities such as:
- Atrial septal aneurysm (more pronounced bulging)
- Lipomatous hypertrophy (increased thickness due to lipid deposition) 1
- Atrial septal defects (actual communication between atria)
The presence of a hypermobile septum should prompt careful evaluation for:
- Associated congenital defects
- Potential for paradoxical embolism
- Arrhythmia risk assessment
Conclusion
A hypermobile interatrial septum represents abnormal mobility of the tissue separating the atria. While it may be asymptomatic, it can be associated with important clinical conditions including paradoxical embolism, atrial arrhythmias, and congenital heart defects. Recognition of this finding should prompt appropriate evaluation for associated conditions and consideration of their management implications.