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Posts Tagged ‘Patent foramen ovale’

  1. Left to right
  2. Right to left
  3. Can be in both directions
  4. No significant flow at all !

Answer :   Every response can be correct

The patent foramen ovale is a physiological orifice , which  becomes  pathological if persist into  adult hood .The incidence is estimated to be about 20 %  of the population (Amounts to 100 crore PFOs roaming  in our planet!). It makes  no sense  to  believe  just spotting  a  PFO  in routine echocardiography be termed  as pathological . But recently  (Adding much to  interventionist’s  delight ! ) the presence of which is being linked with migraine and stroke in young.

The size of the orifice can be from a single millimeter to one centimeter* . The direction of blood flow in PFO   is determined by the mean gradient across the orifice. It has to be  left to right  as the LA pressure is  generally   higher by few mm mercury  ,hence there is a small  tide of flow entering into RA with each left atrial filling or contractile wave .(v and a ). This  quantum is miniscule and has no hemodynamic significance in most life situations.

* Some call( Wrongly ) 1cm PFO  as small ASD.

When can Right to left to flow occur ?

When the right atrial pressure increase more than LA pressure it is obvious  blood can enter LA . It is well-known this occurs  in any pathological situations like RVOT obstruction severe PHT , tricuspid valve obstructions etc.

Physiological  Right to Left flow :

Forced expiration (Valsalva) can cause transient  right to left flow. This  may happen in many real life situations like straining, heavy isometric exercise, blowers, muscians  etc.

Which is clinically  significant ?

Left to right or right to left  ?

Left to right shunting is rarely an issue as there is no systemic  desaturation.

Right to left  shunting  can be  important for two reasons

  1. Arterial desaturation( transient )
  2. Shifting of venous debris into arterial side  can result  in potential paradoxical embolism .(This can be air, clot fat , amniotic fluid etc)  This is the reason stroke in young is closely linked to presence of PFO.

PFOs during positive pressure ventilation

PEEP is a classical example where a right atrial positive pressure ,  shunts the blood in pulsatile manner into left atrium .

Platyponea  hypoxia  syndrome .

This is  postural right to left shunting  across PFO .It  is a less recognised (but a common entity) where -in ,  when the patient  lies down there is a  right to left PFO shunt and transient hypoxia .This is often corrected as the patient sits up. The reason being  the valve of PFO , the   door like flap  which guards  the orifice  ,  is aligned   in such a fashion , it  opens up in a  lying posture(Aided by gravity ?)  , shuts down in  sitting posture .It should be noted  The PFO valve is not a constant feature  . The size  of this valve , the stiffness , the hinge points , ability to  float  are highly variable .Hence the clinical variation in PFO syndrome.

The IAS septal aneurysm is an  important variation where the valve of PFO balloons out into left atrium  may become a nidus for thrombus or a focus for atrial arrhythmias .

Stroke in young  and PFO  :This  topic  deserves a separate article

Reference

Anatomy

Excellent PFO images from Yale university library  ( http://www.yale.edu/imaging/chd/e_pfo/index.html)

 

http://chestjournal.chestpubs.org/content/100/4/1157.full.pdf+html

http://chestjournal.chestpubs.org/content/118/3/871.long

http://www.anesthesia-analgesia.org/content/93/5/1137.full.pdf

Excellent PFO images from Yale university library

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