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Posts Tagged ‘fractional flow reserve’

Fractional flow reserve(FFR) is an  Intra coronary hemodynamic  parameter  promoted recently to assess the physiological impact of a coronary lesion . Though it sounds logically attractive the concept  is sailing in rough seas  .I am afraid FFR is drowning  a fairly useful tool of IVUS  along with it  !

Read this large study on FFR (JAMA June 2014) .It seems to suggest  FFR is a costly and unnecessary accessory in cath lab

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Critical thoughts on FFR

It adds time , money , and procedural risk*  to any given patient .The only possible use is to reduce the proliferating stent usage !But the  irony  is complete as we do our daily business in  modern cath suits .To negate  one indulgence we need to  need to indulge  in  another ! (Junk begets Junk !)

It reflects lack of courage on the part of cardiologists to advice medical management even in obvious low risk lesions !

It is unfortunate ,we need a scientific or  a pseudo scientific tool to lift up our sagging medical intellect !

 

* crossing  delicate and often complex lesions  without any major purpose is bad wisdom !
(more…)

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  1. The concept of  FFR is based on pressure gradient  alone.In any hydraulic model (Both biological and non biological systems ) pressure difference  is the least   important parameter  that determines flow.
  2. FFR  is unphysiological  as hyperemia   is  artificially induced one .(Adenosine  is not the only parameter that determines it !)
  3. Serial obstructions and branch point hemodynamics are  conveniently ignored.
  4. Reproducibility  remains a big question mark .
  5. On safety  issues  FFR  is a suspect.( Often times , it  requires expertise comparable to  that of a  complex  PCI !) .Beware , the FFR unit has stiff catheter system and is an additional health hazard .  I have witnessed   atleast two cases  where  insignificant lesions were  made significant by  FFR related Injury .
  6. And  now the  knock out punch ,  ! Probably the most vital  issue for which FFR should be banished * , it is not taking into account of vulnerabilty of a plaque .( An FFR > .9 with a hanging , eccentric , mid LAD lesion was left alone by one of the  academically up to date ,  evidence  based interventional cardiologist!  )
           (*If perfomed  in isolation without IVUS/OCT  )
I am still wondering how this concept came into cardiologist domain and into the cath lab .It should have  never been let out of theoretical physics labs !
Final message
The best way to assess physiological significance of an anatomical obstruction is  to  do  exercise  stress test .
If  the lesion is  able to sustain good exercise capacity , it  can be deemed physiological unimportant.
While , this is an explicit  proof  in single vessel disease  ,  even  in   multivessel  CAD ,   EST  is   a  collective  measure of  coronary  reserve flow .( Something like instantaneous equivalent of virtual  multivessel  FFR  )
Moderated After thought
FFR is a highly specialized theoretical  tool , that has very limited role in cath lab .
The two major practical (Non academic)  use of FFR   is to shun away  those   internet fed ,  annoying, pseudo  intellectual patients ,  who constantly ask for  angioplasty  for  obliviously insignificant lesions !
FFR comes very handy  to  bail out  cardiologists at  times of distress   ! (To escape  from the wrath of our patients   after a sub optimal &  technically inferior   PCIs   and   in  the  long term confabulations  in   restenosis  after stenting !  )

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How to manage an  asymptomatic 45 year old man with  90 %  mid  LAD lesion  , with  FFR  .9   who is  stress test  positive at 9 Mets  ?

Six  cardiologists and six responses   . . .  and the elusive seventh sense

  1. FFR is most scientific test to assess  physiology of coronary stenosis  . I will  go with that  and put this patient under  medical management.
  2. I agree with FFR, still the  patient has no symptoms  , but why the hell is EST  + ve ?  I am confused  .
  3. I would definitely stent the lesion irrespective of the symptoms .
  4. I would order a stress thallium . I do not believe in FFR
  5. The data provided  is insufficient. I would like to this patient in my clinic , and if necessary  may  order a fresh CAG.
  6. For a 90 % LAD  lesion FFR should not have been done in the first place .That is the root of the confusion. He should have received a stent long back .

Final message

FFR is  a terrible concept   for two reasons . One ,  it never bothers about flow across  a lesion. It simply  relies upon  pressure drop. we all know  there  is an intricate relationship   between pressure and flow . Simple pressure drop can never be  expected to translate into incremental flow in biological systems .The  second major limitation is  it  ignores the  morphology of the lesion . We know an eccentric soft  lesion with a  good distal   FFR  is  live  coronary explosive .

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Fractional flow reserve is  a new coronary hemo-dynamic para meter used to assess physiological impact of border line lesions in coronary artery disease. The calculation is simple

FFR is  a terrible concept * for two reasons .

One ,  it never bothers about flow * across   a lesion. It simply  relies upon  pressure drop. We  know  there  is an intricate relationship   between pressure and flow . Simple pressure drop can never be  expected to translate into incremental flow in biological systems .

(FFR anology  in co-arctation of aorta . Can you take difference between upper limb  BP and lower  limb BP as a most accurate   Index of severity of co-arctation of aorta ?  )

How crude it would be   . . .  to  believe so ?

Two   it  ignores the  morphology of the lesion . We know an eccentric soft  lesion with a  good distal   FFR  is  live  coronary explosive .

The  FAME 1 and FAME 2 studies  glorified  FFR  !  I differ in many ways .

Some of  the  observations made about FFR.

  • FFR is to be  done only in discrete ,  safe looking  , intermediate lesions .(Do not ever attempt it in a eccentric lesion )
  • FFR wire is a  stiff ( stainless steel ) wire .  Careful maneuvering is necessary . Lesion crossing  and pull back  FFR wire require some expertise.
  • FFR / OCT  combo,   increase  not only the  fluroscopy time  ,  this procedure can be  more complex than  the intended   PCI .
  • My colleagues tell me FFR measurements are not often  reproducible .(I have little experience in this )
  • Adenosine induced vasodilatation  is not natural physiological model . Further it has  a potential for  a coronary steal if there is near critical lesion in contra lateral artery.
  • There are many occasions   FFR wire has caused  dissection  and  subsequent stenting was necessary  .(The very thing  the cardiologist wanted to avoid !)
  • Bifurcation lesion FFR measurement is prone for errors
  • FFR in two tandem lesions cannot be assessed   accurately
  • Post PCI FFR is not practiced routinely in may centers  the fear of  status quo of FFR.

Final message

This post is not to defame the FFR as a concept . Just to make you think  . . .  how often ,  we  are entrapped  in a  pseudo -intellectual  game in  the cath lab ! FFR  as a tool , can still  be valuable to assess coronary hemo-dynamics in a selected lesion population especially,  discrete,  single vessel ,  or left main disease  with around 70 % narrowing . But never go with FFR alone .Consider the morphology , location   of the lesion .

Finally do not forget  ,  the   good old  EST  can  give a stiff  fight  for supremacy over FFR  in terms of assessing physiological impact of a coronary stenosis (Especially in single vessel disease ) 

Reference

Fractional Flow Reserve versus Angiography for Guiding Percutaneous Coronary Intervention . http://www.nejm.org/doi/full/10.1056/NEJMoa0807611

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Even as we make rapid strides in  conquering coronary atherosclerosis by all those fancy gadgets , the  fundamental coronary  hemodynamic principle   is poorly understood . Hence  there is no surprise  for the  “perennial ambiguity”  in the indication  and effectiveness of  coronary revascularization .

Why the hell ,   reliving  a  coronary obstruction  may  not provide the   expected hemodynamic benefit  or do not prevent future  heart attack  in many ?    One of my patients  asked ?

I told him . Wait , do not get  excited , we also do not know  . . .We are just beginning to understand mysteries of coronary  circulation.

It is a well documented fact  ( but a  debatable )   that  lesser the  severiity of a  lesion more likely it is prone for an acute coronary  event .( Vulnerability , shearing stress or is it a simply a statistical mirage !) While the  vulnerability aspect is  complex , the hemodynamic  impact of  coronary  lesions  is   relatively better  understood. Here is  an important  documentation from Dr B . K  Koo from  Seoul , South Korea  who has elegantly shown the behavior of  fractional flow reserve (FFR ) in various grades of  stenosis  .This study was done in jailed side branches following PCI.

FFR  shows a surprise   relationship  with severity of coronary stenosis  . Even severe lesions showed equal if not more flow  reserve ?

and mild lesions might have lost all its reserve.

 How is it possible ?  Can it be true ?

Yes , it is indeed a  fact . God generally  keeps a stong link between anatomy and physiology  , structure and function . But he adds a rider and keeps  a reserve in every  human cell   meant for  emergency  back up . FFR is  one aspect of this , we have  partially discovered .  When we fail to understand this we are bound to get confused and make a wrong decision in cath lab.

Simply stated ,  flow across a coronary  artery is much more depedent on the status of microvascualture  than the hurdles they face in the epicardial highways !

Link to this original article from JACC .

How to do the FFR procedure ?

http://www.sjmprofessional.com/Clinical-Solutions/Intl/Radi-FFR.aspx

Soon to follow . . .  If less severe lesions are more  dangerous why we are ignoring it in cath lab ?

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