Hypermobile Interatrial Septum Does Not Typically Cause Positional Murmurs
A hypermobile interatrial septum alone does not cause a murmur that varies with positioning. The murmur you're hearing is almost certainly from an associated structural abnormality—most commonly an atrial septal defect (ASD), patent foramen ovale (PFO), or tricuspid regurgitation—not from the septal hypermobility itself.
Understanding the Clinical Picture
What Causes Positional Murmurs
According to ACC/AHA guidelines, only two specific cardiac conditions produce murmurs that characteristically change with positioning 1, 2:
- Hypertrophic cardiomyopathy (HCM): Murmur becomes louder with standing
- Mitral valve prolapse (MVP): Murmur lengthens and intensifies with standing
All other murmurs typically diminish with standing 1, 2.
The Hypermobile Septum Connection
Hypermobile interatrial septa are frequently found in patients with interatrial communications. Research shows that 43% of patients undergoing AF ablation had structurally abnormal interatrial septa, including hypermobility/aneurysm (often associated with PFO or small ASD), septal flaps, or thickened septa 3. However, the hypermobility itself is not the sound generator.
What You're Actually Hearing
Atrial Septal Defect Findings
When an ASD is present with septal hypermobility, you'll find 4:
- Fixed splitting of S2 during both inspiration and expiration (pathognomonic)
- Grade 2/6 midsystolic murmur at the pulmonic area and left sternal border
- Mid-diastolic rumble at the lower left sternal border (present in 50-75% of cases) due to increased flow across the tricuspid valve 5, 6
The diastolic murmur correlates with shunt volume (Qp/Qs ratio) and occurs more frequently in younger patients with tachycardia 5.
Tricuspid Regurgitation Pattern
If tricuspid regurgitation accompanies the hypermobile septum 7:
- Right-sided murmurs increase with inspiration (Carvallo's sign) 1, 4
- Holosystolic murmur best heard at the tricuspid area
- May facilitate right-to-left shunting through a PFO, especially in upright positioning
Clinical Algorithm
When you encounter a hypermobile septum with a murmur:
- Listen for fixed splitting of S2 → If present, strongly suggests ASD
- Assess respiratory variation → Right-sided murmurs (TR, ASD flow) increase with inspiration 2, 1
- Check for diastolic component → Mid-diastolic rumble suggests significant left-to-right shunt
- Perform bubble study during TEE → Identifies interatrial communication that may not be anatomically obvious 8, 3
Critical Pitfall to Avoid
Do not attribute the murmur to "septal hypermobility" alone. Research specifically demonstrates that septal excursion measurements (0.66 cm vs 0.76 cm) do not differ between successful and unsuccessful device closures, indicating that mobility itself is not hemodynamically significant 8. The murmur arises from:
- Blood flow across an anatomical defect (ASD/PFO)
- Valvular regurgitation (usually tricuspid)
- Increased flow across normal valves due to shunting
Definitive Workup
Obtain transesophageal echocardiography to:
- Visualize the exact septal anatomy (hypermobility is present in 25% of AF ablation patients) 3
- Identify associated PFO (present in 41% of hypermobile septa) or ASD 3
- Assess for tricuspid valve pathology
- Perform agitated saline contrast study in multiple positions if platypnea-orthodeoxia is suspected 7
The positional variation you're observing likely reflects changes in venous return and right atrial pressure affecting flow through an underlying structural defect, not the septal motion itself.