Posts Tagged ‘inter atrial septum’

 Inter atrial septum(IAS)  is a delicate structure , formed by a  “curious IAS  embryological process”  , when  two septums ,  two ostiums  cross each  other .They  fold  and unfold  like  curtains  in different times ,  ultimately result in a  single membrane separating LA and RA  with a  central physiological   hollowness called foramen  ovale .

All along this process ,  blood has to shunt  from  RA to LA  untill the baby comes out ,  when the direction reverses that  result in the flap  of foramen ovale locking  against the septum secundum with raising LA pressure . So , basically the genesis of  IAS is all  about growing,   resorbing  and  sticking of two septums . This starts in utero and continues well after birth. One can imagine  complexity of  the factors that determine the thickness of IAS.

The IAS thickness varies between 2mm to 4  mm . With increasing use of trans esophageal echocardiography and also the need for cardiologists to puncture the IAS , it is becoming important to study the anatomy of IAS in detail.

A new  cause of  thickened IAS  is reported recently .

 This is refered to as Double Inter atrial septum,  fused like a sandwich  with a  potential space  in between  .

The embryological basis is not clear. (A septum primum and secundum fusion ?)

The PFO   is an  oblique orifice in many .It is some times refered to as tubular PFO . A large tubular PFO can mimic a double IAS.

An  aneurysm of IAS  may get  fused to appear like a double septum

or Is it  IAS dissection which  give an appearance like double IAS ?

Personal perspective

  • It is very difficult to embryologically  explain the concept of double IAS .  I would think  , it is  double layer  of single embryological  septum   with a  potential  space  in between .
  • It is possible an intra mural hematoma (Spontaneous or acquired ) may cleave the septal plane and mimic a double IAS   when the   thrombus gets dissolved later.

Other causes of thick IAS

Septal thickness an issue during transeptal puncture . During PTMC and left heart catheterization a thick septum may be a hurdle.

Infiltrative  myopathies especially amyloidosis is known for a very thick non -puncturable IAS  



2. http://www.ncbi.nlm.nih.gov/pubmed/16950474?dopt=Abstract

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This is a relatively common abnormality of IAS. It is  often observed  as  IAS bulging  into left  or right atrium  in routine echocardiogram.If this happens without  atrial hypertension it is termed as IAS aneurysm .

This is due to valve of foramen ovale bending into the RA/LA*  cavity for various distance. By definition , the radius of curvature of  the bulge should be more than 10 mm to label it as IAS aneurysm.

*Bulging into RA more common

Click on the Image to see the animation

General features

  • Mostly a benign entity.
  • More often observed  in  association with PFOs or ostium secundum ASD.
  • When occurs in isolation does not result in any shunting across it
  • The septal bulge can be static or  dynamic . It could swing  into LA, RA, and back to LA or vice versa.
  • Anatomically 5 types are proposed.
  • Multiple fenestration in the aneurysms have been noted.
  • Aneurysm  formation may aid in spontaneous closure of ASD.

Clinical  implications

  • IAS aneurysm tend to aggravate  stasis of LA  blood flow and predispose to minute LA clots and systemic thrombo embolism .
  • IAS aneurysm can act as an arrhythmic focus , generating focal atrial tachycardias.
  • A non ejection click  may be occasionally heard as  the IAS aneurysm  bulges and tenses within LA/RA cavity .


1 . Olivares -Reyes A, et al. Atrial Septal Aneurysm: A new classification in 205 adults. J Am Soc Echocardiogr

2. Longhini C, et al. Atrial septal aneurysm: echocardiographic study. Am J Cardiol 1985;56:653-67.

3. Gondi B, Nanda NC. Two-dimensional echocardiographic features of atrial septal aneurysm. Circulation 1981;63:452-57

4. http://www.fac.org.ar/revista/00v29n4/congreso/premio3.PDF

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