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Posts Tagged ‘post stenotic dilatation’

Laws of fluid dynamics dictate there is a pressure drop across   a point of narrowing  and recovery  thereafter  . At  recovery point if the vessel wall is weak it tends to balloon out .This is called post- stenotic dilatation .This is  the anatomical equivalent of Bernoulli or venturi  effect. This theoretically  occur only distal to obstruction .

How do you explain the common observation of pre- stenotic dilatation?

  • Intimal weakening due to disease process is the prime  suspect.
  • Pre stenotic  increment in mean pressure  also play a role .
  • Mechanical distention due to stagnated blood  proximal to  critical obstruction  is  a  logical explanation.
  • Finally and most importantly ,contagious , sub – angiographic  atherosclerosis.

How is  dilatation  different from ectasia ?

May be they are all related phenomenon. The definitions  of ectasia ,  dilatation, aneurysm are  more to do  with semantics than with academics.

Clinical and hemodynamic implication in cath lab

  • Sluggish  flow prone for thrombus
  • Stent selection errors likely
  • Stent dislodgment  and migration

Long term effects

  • In stent re-stenosis is more common if adjacent segment show dilatation.

Finale

Enlargement of vessel wall in both pre and post stenotic segments are possible . In small vessels pre- stenotic dilatation is  more common , while in large vessels post stenotic dilatation is  more prevalent .(Aorta, Pulmonary artery)  The mechanisms are slightly different. Apart from the lesion tightness ,  hemodynamic  and genetic factors are also responsible These dilatations are  often labeled as ectasia in coronary artery  and  most cardiologists  tend to   ignore this finding especially if  the margins are smooth.

But , newer imaging modalities like IVUS, OCT have given   better  insight about these dilatations.These   are  actually an  expression  of the  contagious  atherosclerosis .  Pre-  stenotic segments are prone for extensive disease  than even the diseased segment due to  more hemodynamic turbulence. There is some evidence atherosclerosis progresses  proximally more than distally.Smooth margins within the  pre -stenotic dilatation  does  not guarantee  disease free status.

During PCI  there could be  an  argument for covering the dilated  pre- and post stenotic segments  as well* . (We vouch for endovascular stenting when aorta is dilated why  do we hesitate  in coronary  ?)  .Careful selection of  coronary stent size  is  recommended  and  allowance should be given  for these two (Pre and post coronary dilatation ) patho -anatomic phenomenon.

* Stent missing a lesion is stylishly called geographical  miss ! This should logically include dilated segments also.

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Newtons third law of motion  says for every  action  there is  an equal and opposite  reaction .

In vascular hemodynamics  whenever there is a an obstruction , there tend to be a dilatation of   the same blood vessel  somewhere distally.

It may not be linked to newtons law but it is  observed in many .It is more common in large vessels than small ones.

Here is a patient with a tight LAD lesion with a significantly  dilated segment located immediately beyond the  obstruction.This can be considered as a post stenotic dilatation. Coronary ectasia is  also a  possibility but since it is related to site of obstruction the former is likely .


What determines the post stenotic dilatation ?

The exact mechanism is not clear. There is  a definite ,sudden  pressure drop distal to  the  obstruction. This  pressure drop  recovers beyond a certain distance . At this point ,  the rate of increment in  velocity of   peaks .This somehow has an effect on the  distending  pressure  and the adjacent vessel wall gets radially stressed and begins to dilate. (Opposite of what is expected in Bernoulli effect ?)

Is there a anatomical defect in  post stenotic dilatation ?

Not every  one goes for post stenotic dilatation.There is a possibility it occurs only in genetically susceptible individuals .

Significance in  interventional cardiology

The post stenotic segment has a potential to misbehave in the period following  PCI . If the distal instent stenosis  occur (even if it is minor ! ) it can induce a cycle of post stenotic eversion of normal segment and risk of edge effect or stent thrombosis is more.

Read also Glagovian phenomenon – A form of  intra stenotic coronary artery dilatation

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