- 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.
- FFR is unphysiological as hyperemia is artificially induced one .(Adenosine is not the only parameter that determines it !)
- Serial obstructions and branch point hemodynamics are conveniently ignored.
- Reproducibility remains a big question mark .
- 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 .
- 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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Dr.S.Venkatesan MD 
An FFR > .9 with a hanging , eccentric , mid LAD lesion was left alone… then what else do we do seal the plaque..show me the evidence to seal palque.
And u say EST(exercise) is great…please check its sensitivity and specificity ! EVEN MPI has a dozen setbacks like balanced ischemia ! SO what to do ? Look its a quest to determine significance … anatomical/physiological .
I find that u want FFR to give u lesion morphology and u say its bad ! Cone on u cant compare apples with oranges..both are different. Ideal lesion imaging is a combination of Physiological + Intracoronary imaging . But costwise its not feasible in india. so again there r issues.
FFR is not perfect… but it is the best we have. With the least possible assumptions. And what else do u need when u have such strong data backing it…DEFER , FAME, FAME2 !!!
It prevents needless stents …but i guess most cardio’s want it in !
And talking of reproducibility …well just ref to Prof Koo … the way to taking good readings [TCT lecture]
And if u dont like adenosine ..they are developing the iFR !!