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How does VSD affect the conduction system of heart which is dangerously close to it ?

Posted Jun 15 2010 8:21am

VSD is  the leading  cause  of   congential heart disease .

  • The natural history is wide open , from totally asymptomatic  , incidentally detected in   childhood to a fulminant cardiac failure  and death in early  infancy .
  • Many small VSDs get closed by year 10. None of the large VSDs close spontaneously.Few of the moderate sized VSD may get closed.
  • The site of the VSD is a major determinant of spontaneous closure. Muscular  VSDs are more likely to get closed .Of course many of the membranous VSD have  at least a rim formed by a adjoining muscular septum
  • Associated defects, RVOT obstruction and late onset AR also has a  influence  on the natural history.
  • Progressive PHT  leading onto   Eisenmenger  syndrome  occurs  has become a diagnostic curiosity in many countries .

It  is natural to expect  the VSDs   to share a  close relationship with  the conduction system which   fights for  ”equal rights”  to occupy the inter ventricular  septum  , (In spite of   a defective septum ! )

How often we see conduction defect in VSDs ?

It is  rather surprising  to note   conduction  defects are not  common in VSDs .In fact it can be termed  rare . How  this is  posssible ?   VSDs , however large it maybe   ,  usually spares the conduction system . This is simply due to the fact , developmentally the two systems  , ventricular septum and the electrical  system  of the heart comes from different embryological focus and and are simply anchored together.

If the IVS is not formed properly ,the bundle  of His and it ‘ s major right and left branches  are  simply displaced  and not are  destroyed  ,  they  tend to occupy  one of the rims of VSD

*Further, a VSD located peripherally and distally towards the apex has little impact on the conduction tissue as it has already fanned out and small little twigs are affected ,while central , proximal,  and basal VSDs  can have more significance .

Classically ,  it has  major  significance   for the  surgeons than cardiologists  , as post operative blocks are more common than the preoperative blocks !

What are the  changes to the conduction system in various VSDs ?

Membranous VSD

  • Migration  of  A-V node   posteriorly toward crux of heart *
  • His bundle  courses  along  the  posteroinferior rim of defect

* This makes sure the compact AV node never comes into picture of VSD . It  also it explains the  rairty of   complete heart block  due to mechanical damage  to the  AV node  by the  VSD jet

How to avoid  injury during surgery ?

Sutures  are  made a few millimeters from postero-inferior rim,  Do not penetrate  the septum.  Suture along  RV side  of the  septum  as the  His bundle  is  often located on the  LV side of muscular septum.

RV approach to close VSDs,  make  postoperative RBBB a common issue but generally it has no great clinical significance

Location of conduction defect in various  VSDs

  • Membranous VSD  -  Conduction tissue runs along posteroinferior border of defect
    Muscular VSD
  • (Especailly with Inlet extension)  – conduction tissue is anterosuperior to defect
  • AV canal defects . This is the only type of VSD where serious defects of conduction occur  .Interruptions can also occur in the AV node.

Coming  soon . . .

Where  will the conduction system run in single ventricle where there is no IVS ?


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