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Posts Tagged ‘av node embryology’

AV nodal tissue is a not compact structure as we would be believe  . But it is a fact ,  AV  node  do attempt  to compact after birth.

It is never complete.

Note the islands of his bundle entrapped .   Image source : M. Paz Sua´rez-Mier J Am Coll Cardiol 1998;32:1885–90 From the Section of Histopathology, Institute of Toxicology and †Department of Pathology, La Paz Hospital, Madrid, Spain.

All specialised cells should coalesce  to form the compact zone .This fails to happen in many . Failure of AV nodal compaction  results  in islands of slow conducting cells in around AV node . Some of them can mutate  , and   acquire fast conducting properties as well . (Accessory pathway )

This failure of AV nodal compaction is termed as  persistent fetal dispersion of AV node .

In the his bundle  same phenomenon is called as his bundle  de-fragmentation .These abnormalities are noted in pathological  specimens  of  Pokkuri sudden death in Asians .

Unexplained sudden deaths and instant bradycardias and complete heart blocks are related to these dispersion of  AV nodal cells downstream . This also explains some of patients with infra hisian escape show junctional characteristics.

Many cardiac pathologists have observed this . Still  there is a  missing  link  .

References

M. Paz Sua´rez-Mier,Carlos Gamallo  J Am Coll Cardiol 1998;32:1885–90) Atrioventricular Node Fetal Dispersion and His Bundle Fragmentation  of the Cardiac Conduction System in Sudden Cardiac Death

Kirschner RH, Eckner FAO, Baron RC. The cardiac pathology of sudden,unexplained nocturnal death in Southeast Asian refugees. JAMA 1986;256:2700–5.

Hudson REB. The conducting system: anatomy, histology and pathology in acquired heart disease. In: Silver MD, editor. Cardiovascular Pathology. New York: Churchill Livingstone, 1991:1367– 427.

James TN. Normal variations and pathologic changes in structure of the cardiac conduction system and their functional significance. J Am Coll Cardiol 1985;5:71B– 8B.

James TN, Marshall TK. De Subitaneis Mortibus XVIII. Persistent fetal dispersion of the atrioventricular node and His bundle within the central  fibrous body. Circulation 1976;53:1026 –34.

Persistent Fetal Dispersion of the Atrioventricular Node  Association With the Wolff-Parkinson-White Syndrome Claude Brechenmacher, MD; Jean-Paul Fauchier, MD; Thomas N. James, MD Arch Intern Med. 1980;140(3):377-382.

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Most  cardiologists  are familiar with  “Circulation” . We know  it  is a top  cardiology  journal with highest impact factor.  Few of us are  aware  of  a journal called  “Circulation  research” ( I wonder  why it is named  like that ,  as if  the regular   circulation journal  does  not carry research stuff  !)

It is one of the  path breaking   journals that regularly  churn out state  of  the art , often  mind  boggling research stuff.  Once in while we should get a feel of  basic science  research  as it  happens.

How else we are going to know an  atrial cell is to be bio engineered  shortly to behave like a  SA node  in patients with sinus node dysfunction. (Biological pacing )

This team from academic  medical  centre Amsterdam   should be credited   for  publishing   this gem of  an  article   from  a  study  involving the  measly mice !

It  deals elaborately  about the embryonic basis of AV nodal  disorders  . Specifically it  explains  the genesis of  WPW syndrome and how AV rings get muscularised  .

(It  is  due to   error in  bio-genetic forces ,which  affect the    incorporation  of AV nodal tissue  in the  fibrous  skeleton .This   results  in ectopic  junctional  tissues appear   any where along  the AV ring . This is the basis of  accessory AV pathway and   clinical  re-excitation.)

Final message

Once in a while  we should develop the habit of reading  tough  journals  like circulation research . After all ,   if a cardiologist  is not reading   these stuff who else  . . . will  ?

Reference

http://circres.ahajournals.org/content/107/6/728.full.pdf+html

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