right to left shunt across pfo | Dr.S.Venkatesan MD

Posts Tagged ‘right to left shunt across pfo’

What is the link between Migraine and PFO ?

Posted in cardiology -congenital heart disease, cardiology -Therapeutics, Cardiology -unresolved questions, cardiology congenital heart disese, cardiology-Anatomy, Infrequently asked questions in cardiology (iFAQs), tagged migraine and pfo, pfo, right to left shunt across pfo, vasoactive amines cross the pfo, young stroke and pfo on June 27, 2011| 1 Comment »

The link between migraine and PFO is . . .

Incidental & man-made
Almost certain
Definite
A wild imagination

Answer : One of the above is correct , but we do not know which one is !

There has been many patients with TIAs , cryptogenic strokes , who had documented PFO ,complain of prolonged head aches . This was the beginning of suspicion of PFO as a cause for migraine .Then the device industry foresaw a huge opportunity . Things began to unfold and the concept is currently as nebulous as it can be .

Mechanism of migraine in PFO

(All are presumptions )

Right to left shunting of vasoactive amines from venous circulation (Serrotonin) which bye- passes the lung where they are supposed to get filtered.
Venous micro emboli (Antiplatelet agents reduce migraine as well as TIA ! )
Hypoxia transient – cerebro vascular hypersensitivity
Atrial naturetic peptide spills more into systemic circulation through PFO

Counter arguments

If right to left shunting is causing the migraine , why it is not fully disappearing even after closure of PFO (MIST data with starflex device , migraine persisted in a significant chunk !)
What is the incidence of migraine in the prototype right to left to shunt situations like TOF, Eisenmenger , pulmonary AV fistula ? if shunting is the mechanism , logically migraine incidence should be very high in this population , but it is not .
Migraine occurs in 10 % of population, PFO is present in 20% . What are the chances of over lap ? It could be the simple statistics at play !

Where is the evidence ? The mystery called MIST study.

This study , done in UK generated more controversy , which it was supposed to remove . Still this study is considered to be a major evidence for the link between PFO and migraine . Star flex device was promoted by NMT medical Boston .

http://www.medscape.com/viewarticle/541260

Link to best review article on PFO

http://chestjournal.chestpubs.org/content/130/3/896.full.pdf+html

Final message

The link between migraine and PFO can be a fact or myth depending upon our belief in current methods of research in science. The issue is debatable . Of course , one issue is probably closed forever , even if they are linked casually (or seriously ) device closure can never be a sensible treatment option for migraine ! *

We expect a proof / disproof in this mysterious migraine -PFO hypothesis very shortly. Of course , many cardiologists already have their own conclusions !

*Please note , PFO device closure for stroke in young is a different story

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What is the direction of blood flow across patent foramen ovale(PFO ) in otherwise normal adults ?

Posted in Cardiology - Clinical, Cardiology -Interventional -PCI, cardiology -Therapeutics, cardiology-Anatomy, tagged ias septal aneurysm, la pressure vs ra pressure, migraine and pfo, Patent foramen ovale, peep and hypoxia due to pfo, pfo, platypnea ortho deoxia, right to left shunt across pfo, young stroke and pfo on June 26, 2011| 1 Comment »

Left to right
Right to left
Can be in both directions
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

Arterial desaturation( transient )
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)