Retroperiton

Atrial Septal Defect

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* ASD (Atrial Septal Defect ) accounts for 10% of all congenital heart disease.
- Ostium secundum defect is the most common type and accounts for 60-70% of all case.
- Ostium primum type accounts for 15-20%
- Sinus venosus type ASDs are seen in 5-15%

*Defects may be identified in atrial septa by 2-D studies. The direction of flow across such defects can be shown by color flow mapping and the velocity of the jet across the defect can be measured (and hence the pressure gradient identified) by continuous wave Doppler.
* TTE (tarnsthoracic echocardiography) and TOE (transoesophageal echocardiography) are both good at diagnosing ostium primum or Ostium secundum ASDs but TOE is better than TTE in diagnosing ASDs under 10mm diameter. Most clinically and haemodynamically significant ASDs should be diagnosed by TTE. However, TOE should be considered where left to right shunting is suspected but not proven on TTE (even after contrast study) or where a small defect may be significant, e.g. after trans-septal puncture at catheterization.
* Doppler echocardiography may be helpful in demonstrating flow across the atrial septum. It typically shows biphasic pattern (systolic and diastolic) with a small right-to-left shunt at the beginning of systole. Largest shunt flow (left-to-right) occurs in late systole.
* Contrast studies are often useful in determining whether there is flow across the IAS. Contrast may be seen shunting from RA to LA in the presence of an ASD. A bubble contrast study may be positive even when no obvious flow is detected on color flow mapping.
* Real-time echocardiography is helpful for identifying additional abnormalities, such as mitral valve prolapse and a double orifice mitral valve (seen in 3% of patients with ostium primum defect).

Differential :
The inter-atrial septum (IAS) is often thin and in certain views in normal individuals (especially the apical 4-chamber view) there can appear to be a defect in a normal septum, giving the false illusion of an ASD. This is due to an effect known as 'écho drop-out' which happens because the reflected echo signal from the IAS is weak. The IAS in this view is being hit along its edge by the ultrasound beam and is at a large depth from the transducer. By examining the IAS from other views (e.g. subcostal), it can be seen that it is intact.