Posts Tagged ‘coronary hemodynamics’

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 ?


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

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Thousands of  coronary angiograms are done every day. Cardiologist no longer get excited to see exotic coronary lesions .Still , some images can be striking and dramatic. Here is an angiogram from a middle aged man  with stable angina  , who was  one among the routine early morning diagnostic studies  in our cath lab.

Who chopped the neck of this LAD ?

How this man was able to fill up the distal LAD almost completely? (With a complete cut off  right in the neck of LAD )

Are you sure there is antegrade flow ?

Do you get any clue ?

  • Can a trickle of  ante grade flow  sustain  a  TIMI 3 FLOW  ?
  • Or is it a  very efficient  instant collaterals  from LCX ?

Yes . The first one is right . An almost invisible antegrade channel  doing a exemplary job !

How is it possible ?

Realize an important fact . The distal flow beyond an obstruction  is not primarily dependent on degree of obstruction but the status of the distal vascular  bed .  If it is normal  even a hair-line patency  can  profusely perfuse the distal myocardial segment. This is what is happening to this man with a stable angina and perfectly normal micro vascular bed.

Lessens  from this Image.

Do not get fooled by the lay man’s logic. Realise there is  no simple relation  between  the degree of obstruction and degree of  blood flow impediment.It can be linear , curvilinear , or even inverse depending upon   the evolution and timing of obstruction  ,  number of lesions , presence or absence of collateral support , finally and  most importantly  the integrity of microvascular bed .

The  distal vascular bed drops its resistance drastically  once it senses  the problem in  proximal segment . This is based on Bernoulli principle and  is akin to how a  garden hose pipe  can simply increase  the velocity  by tightening the nozzle.*

* The garden hose analogy is a gross simplification of   complex factors that determine coronary blood flow.But it effectively clarifies a point ie  coronary blood flow is least dependent on coronary  stenosis (until  very late stages)

**Note further : This  hemodynamic  principle may not apply in acute occlusion as in STEMI  , where   acute  obstruction  often has a linear relationship with the quantum of blood flow.

By the way what happened to the above patient ?

Since he had significant angina there were no debates regarding management.  He  is posted for elective PCI this week-end .(We  can’t  get a stent just like that unless it is a real emergency  .Ours is a  Govt hospital !)

What is your take . Is it a going to be tough cross ?

I feel so , but my colleague Dr Gnanavelu   strongly  differs !

Let me post  our experience during PCI shortly.

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