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Development of interatrial septum and its defect (ASD)

Atrial septal defect is the most common congenital heart diseases in adults. Intratrial septum is developed from septum primum and septum secundum.
Septum primum forms the lower part of atrial septum
Septum secundum forms the upper part of atrial septum.

There are 4 different types of atrial septal defect which include :
  • Ostium secundum type of ASD seen in 70% cases.
  • Ostium primium type of ASD seen in 20% case
  • Sinus venosus type
  • Coronary sinus type
Ostium secundum type of ASD is developed from septum secondum which is also called as fossa ovalis.
Ostium primum type of ASD develops from septum primum. It is also called as partial AV canal defect.
Sinus venosus type is situated superior to fossa ovalis in relation to the superior venocaval opening into the right atrium. 
Coronary sinus type the defect is seen near the opening of coronary sinus.

Following associations are seen in atrial septal defect
Ostium secundum – May be associated with mitral valve prolapse and partial anomalous pulmonary venous connection on right side.
Ostium primum ASD – is associated with left mitral or tricuspid valve and first degree heart block.
Sinus venosus ASD –may be associated with partial anomalous pulmonary venous connection.
Coronary sinus – May be associated with superior venacaval opening into left atrium.
Syndromes in relation to atrial septal defect
Down syndrome patients have higher rates of ASDs, 
Ebstein's anomaly about50% of individuals with Ebstein anomaly have an associated shunt between the right and left atria, either an atrial septal defect or a patent foramen ovale.
Fetal alcohol syndrome 25% of patients with fetal alcohol syndrome has either an ASD or a ventricular septal defect.
Holt-Oram syndrome – Both the osteium secundum and osteum primum types of ASD are associated with Holt–Oram syndrome
Lutembacher's syndrome – the presence of a congenital ASD along with acquired mitral stenosis.

SCIMITAR syndrome
What is SCIMITAR syndrome: Here there is fatal or patial anomalous pulmonary venous drainage into the inferior venacava

Lutembacher syndrome 
It is congenital ASD with acquired mitral stenosis.