Posts Tagged ‘lapalce law’

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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Human heart is a vital bundle of muscle  weighing  about 300-400 grams. The blood  supply of this muscle  mass  is highly variable . Some areas are abundantly  vascularised ( eg -IVS.) Some areas have a balanced blood supply  or   twin blood supply (Often the  LCX and RCA in the  crux of the heart ). Certain areas have a precarious blood supply . They are  some times called as water shed areas or  the vulnerable  (The Bermuda triangle of the heart ) overlapping zones of   of  LV apex,  LV free wall and  the anterior surface. This  is  often a  no man’s  land .Every major arterial branch  ignores  this area  and shrug of their responsibility .

This  is the reason ventricular free wall and IVS rupture is more common in this area  making the  mechanical complication  a leading cause of mortality in STEMI.

Similarly , even among the survivors , this area is more prone for aneurysmal  dilatation and adverse remodelling .Though . this  is related more to the LV stress distribution (Laplace law)  , early softening  due to watershed infarct of LV apical zone , also play  a major role .

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