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Unusual Atrial septal defects : Sinus venosus type of ASD .

Posted Aug 06 2009 10:35pm

Atrial  septal defects  are one of the commonest forms of congenital heart disease.

  • The commonest being the ositum secundum ASD     ( Which is in fact is a defect in the development of septum primum)
  • The next common is ostium primum defect which is a part of AV canal or atrio ventricular septal defect.

Other forms of ASD include

  • SVC type /Also  called sinus venosus type of ASD .
  • IVC type
  • Coronary sinus defect -Also called partial or complete forms of unroofed coronary sinus

asd svc asd sinus venosus

SVC type ASDs

They are in the strict sense can not be called as ASD. This is because there is no defect in  any of the  embryological  inter atrial septal component.

There is no direct communication between RA and LA, instead   a window  or passage of communication   between pulmonary vein and SVC. Right upper lobe pulmonary vein  is usually the culprit .Some times more than one PV  communicates with SVC.

The exact area of this PV-SVC window occur between anterior surface of right upper lobe PV with postero lateral surface of SVC.

PAPVC partial anomalous pulmonary venous drainage can be considered an integral part of this defect as RUPV is linked with SVC.

Can we have a combination of SVC ASD and OS ASD ?

This is possible .But two embryological errors need to occur. This is often seen as a large OS ASD with deficient or absent superior rim. So whenever superior rim of IAS is deficient a PAPVC and a SVC ASD should be looked for.

Clinical features

  • SVC type ASDs  generally shunt lesser blood than OS ASDs. (Often<2:1) .This is because it is not the LA that is communicating with RA instead only a
  • It is usually a single PV (some times 2) that shunts from left to right.

There is a distinct possibility of missing this lesion in routine echo.Minimal RA,RV enlargement may give us a clue.The classical subcostal or  4 chamber  view in echocardiography may not visualise  these defects.

So, whenever one encounters mild dilatation  of RA and RV and the IAS appears  intact, a meticulous search and a focused echo in the superior aspect of IAS is warranted. Angled  superior views may pick up this defect.A transesophageal echocardiogram (TEE) is often required to  confirm it.

Therapeutic issues

  • Device closure is not possible
  • Surgery involves little more technicality than ASD OS.
  • Small defects can be patch closed.
  • Some times the SVC has to be disconnected from the PV and anastamosed separately on right atrial appendage. SVC resection  will  aid the surgeon in proper patch closure.
  • Post operative follow up is necessary as SVC obstruction or PV obstruction may be a delayed consequence

References

svc asd sinus venosus

http://ats.ctsnetjournals.org/cgi/content/full/59/6/1588?ijkey=4f42649bc5805f3cf

http://asianannals.ctsnetjournals.org/cgi/content/full/10/3/231

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