Posts Tagged ‘dynamic vs fixed obstruction in tetrology’

RVOT obstruction is the  sine qua non of TOF. It is  traditional to believe the obstruction  in TOF   is dynamic and is located in the infundibulum. It may be true in a broad sense .But  in reality  the  blood flow faces  too many hurdles within the RV before it reaches the pulmonary artery  and lungs  there after.

The commonest and most important one being the mal-aligned conal septum encroaching the infundibulum .(This anterior migration of conal septum is responsible for the aortic  over ride and  VSD as well) .It is erroneous to  think  the RVH in  TOF is simply an after effect of RVOT obstruction .There  can be  intrinsic defects in the RV trabecuale  that hypertrophies and  traverses the RV cavity  in  randon fashion.

Soto described 6 types of obstruction in TOF in elegant anatomic and pathologic study in 1981. Every cardiology fellow must read this original article before going to the Board examination. http://circ.ahajournals.org/content/64/3/558.full.pdf+html

For some reason  God  has  not  arranged  the   RV inflow , body  and out flow  in a linear  fashion . ( ? Meant  for haemic  acceleration in the low pressure venous circuit  )  .In  TOF this becomes important.  It is curious to note even minor  muscle bundles that  criss cross the RV body  act  as a speed breaker and alter the stream and direction of blood flow  .This  is why ,  TOF  can generate   systolic murmurs in various shapes and  time  over the left para-sternal area .(In TOF one can get a murmur right from left  2nd space to well down the lower sternal area )

What are the fixed obstruction in TOF ?

The  resistance  to  blood flow  within the RV  is often multiple ,  extend  from RV body to  pulmonary arterial branch points. It is important to realise few of the obstructions are fixed in nature.  Differentiation of dynamic vs static obstruction  is important in therapeutic aspect also. The efficacy of beta blockers is directly related to the ratio of dynamic vs fixed resistance .

Hypertrophied  trabecuale sept0 margianlis (TSM) usually offers fixed resistance. The infundiubulm is the only place where one can expect a dynamic component . If the annulus and valvualr PS  caused more of a  fixed obstruction

Final message

So,  fellows beware if some one asks this  question “Where is the site of obstruction in TOF ”  .Be ready with an elaborate answer . It is better to classify according to sites  of obstruction   with specific  reference to  dynamic or static nature .


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