Definition
- ASD located at lower part of IAS with both AV valves at the same level.
Embryology
- Septum primum has an inferior defect called ostium primum. Normally this closes by growth of endocardial cushions. Here it fails to close.
- Other defects of endocardial cushion may be present like cleft mitral valve.
Incidence
- 20% of all ASDs.
- Females are 2 times more affected.
Hemodynamics
-
If MR is present,
-
Increase in left to right shunt leading to
- Chance of HF in infancy
- Earlier onset of symptoms of ASD
- Earlier occurrence of PVOD
- MR itself can cause heart failure
-
- Does not close spontaneously.
Clinical features
-
MR-
- PSM at apex
- MR murmur is not modified by onset of PVOD.
-
If MR is present, the findings of ASD may be modified
- Prominent v wave in JVP
- LV type apex
- IE may occur (unlike secundum ASD)
ECG
- Incomplete RBBB pattern in v1 as in secundum ASD.
-
Features peculiar to primum ASD are-
- First degree heart block in 50% cases.
- Left axis deviation (-20 to -60 deg) is always present.
- q in I & avL (counterclockwise loop).
- qRs in v5 & v6 due to LV volume overload.
Chest X-ray
- RA, RV and LV enlargement.
- LA is inconspicuous despite MR due to presence of ASD. Thus enlargement of all chambers except LA.
Echocardiography
- ASD in inferior septum.
- AV valves at same level.
- Cleft in AML at 12 O’clock position.
- MR.
Cardiac catheterization
- Catheter from RA to LA to LV has a low horizontal course.
- PA pressure is more than in secundum ASD.
- Goose neck deformity of LVOT may be present.
Differential diagnosis
- Complete AVSD
-
Secundum ASD with rheumatic MR
- PSM radiates to axilla
- Left axis deviation excludes this diagnosis
-
Common atrium
- Symptoms occur earlier than primum ASD
- Mild cyanosis is present
- Howell-Jolly bodies due to asplenia may be present
Management
- Mitral valvuloplasty with ASD closure.
- Done between 1 and 2 years of age even if shunt is small and even if MR is not significant.
