Maximum Device Size for 12 mm ASD
For a 12 mm secundum ASD, the appropriate device size typically ranges from 14-18 mm, with most operators selecting a device 2-6 mm larger than the measured defect diameter.
Device Sizing Principles
The sizing of ASD closure devices depends on the measurement method used and the specific device selected:
Measurement-Based Sizing
Balloon stretched diameter (BSD) remains the traditional gold standard for device sizing, though modern imaging has challenged its necessity 1. For your 12 mm defect:
If measured by 2D transesophageal echocardiography (TEE): Expect the actual stretched diameter to be approximately 6 mm larger (based on the mean difference between TEE and BSD measurements) 2. This would suggest a stretched diameter of ~18 mm.
If measured by balloon sizing: The device is typically selected to match or be 1-2 mm larger than the BSD 3, 4.
If measured by 3D-TEE: Device sizing correlates well with 3D measurements, though there's a tendency toward more undersizing with this method 5.
Device-Specific Considerations
For the Amplatzer Septal Occluder (ASO), which is FDA-approved and widely used 1:
- Device size is typically 2-3 mm larger than the defect size 6
- The ASO has successfully closed defects as large as 38 mm 1
- For a 12 mm defect measured by TEE, a 14-15 mm device would be typical
For the Occlutech Figulla Flex II (FSO):
- Device size is typically 5-6 mm larger than the defect size 6
- For a 12 mm defect, this would suggest a 17-18 mm device
For the GORE HELEX occluder:
- Suitable for small to moderate defects up to 18 mm 1
- A 12 mm defect falls well within its range
Critical Anatomic Factors
Device size selection must account for more than just defect diameter 1:
- Rim adequacy is the key limiting factor, not absolute defect size 7
- Adequate surrounding rims are essential for device stability
- Aortic rim deficiency (present in 50% of patients) influences device selection but doesn't preclude closure 6
- The length of the interatrial septum matters less than rim quality 7
Practical Algorithm
- Measure the defect using TEE (2D or 3D) and/or balloon sizing
- Assess rim adequacy around the entire defect margin
- Select initial device size:
- ASO: Add 2-3 mm to measured diameter
- FSO: Add 5-6 mm to measured diameter
- Confirm sizing with TEE guidance during deployment 1
- Be prepared for technical modifications - standard deployment succeeds in only ~35% of small patients; modified techniques are often needed 7
Important Caveats
- Oversizing risks: Device migration, erosion, and cardiac perforation can occur regardless of sizing strategy 6
- Undersizing risks: Residual shunt and device embolization
- The correlation between TEE and balloon measurements shows that TEE typically underestimates by ~6 mm compared to stretched diameter 2
- For a 12 mm defect, you're well within the range for percutaneous closure, as devices up to 28 mm have been successfully deployed even in small children 7
The final device size should be determined at the time of the procedure using real-time TEE or intracardiac echocardiography guidance, allowing for adjustment based on device stability and position across the defect 1.