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Posts Tagged ‘vulnerable plaque’

Is “Non-flow limiting coronary  lesions  more prone for ACS ?

  • If  your  answer  is “No”, you can skip this article.
  • If your  answer is “Yes” , you need to read this article.

ACS is the commonest cardiac emergency .Thousands of patients are treated every day.Millions of dollars are spent.Bulk of the cardiologist’s life revolves around this entity.

Scattered atherosclerotic plaques in coronary artery lead to ACS either in a random fashion or in a predictable manner .

Still, we are  highly  uncertain about  which lesions are likely to result in ACS ! Some time in the beginning of  21st century, the main stream cardiology media were abuzz with the concept, that non obstructive , non-flow limiting lesions are more prone for ACS rather than more tight  stenosis.

atherosclerosis  flow limiting lesion  glagov  plaque rupture vulnerable erosion fissure vs dissection

I fail to understand how a tight lesion is less  prone for ACS. Tighter lesions are  bigger and must be  prone for more complications . Image courtesy :http://upload.wikimedia.org/wikipedia/commons/9/9a/Endo_dysfunction_Athero.PNG

This reasoning was based on few studies, that lacked  solid scientific proof . In fact the initial  observation was  not made in living coronary arteries rather by autopsy observations .(Later live virtual histological studies came ,  but didn’t confirm this !)

Surprisingly the degree of  anatomical narrowing was conferred  vulnerability  , when we know plaque compositions , morphology and hemo-rheological  factors are many fold important in precipitating ACS . (Lipid content , fibrin cap  thickness, eccentricity , etc)

So where is the truth hidden?

Is it really possible, lesser the stenosis more  is the propensity for rupture ?

 We need to introspect .

“In all probability,  it is a meager statistical illusion”

For every tight lesion there are as many minor lesions scattered around in a given a coronary artery. These can progress into ACS  later.

It is basically wrong to assume non-flow limiting lesions are more prone for ACS than non-flow limiting lesions.To believe so , seriously underestimates  the  culpability of big lesions .It appears a coronary mockery to me  !

At best , we can conclude  non-flow limiting lesions  are not benign and can be an important source of ACS.

An unscientific chain reaction !

If we start believing non flow limiting (say  30%  stenosis ) is more prone for ACS , why we are not stenting all  those lesions ?

If the above concept  is  is applied in cath lab  routinely , the principle of  FFR   which relies solely on hemodynamic impact  will  crash into the dustbin !

Some  more truths

However , It is indeed true  when a plaque is hardened by severe sclerotic process or calcification it is less prone for  rupture and clinical ACS  but can be a source for stable angina.

Is it  justified to assume , larger the plaque the harder  would be it’s content  that  resists ACS ?

Meanwhile , we also know there need not be any lesion at all to cause an ACS.( In a young  smoker ,  100 % thrombotic STEMI  is possible  over an area of coronary erosion caused by endothelial dysfunction ! So , where do we go from here !)

Let us be clear

Are you confused more !   . . . after  reading this article, let us clear it by two-line summary !

As on 2014 ,

  • Symptomatic flow limiting lesion   are tackled by stents.
  • All non-flow limiting lesions  are treated by  high dose Statins  and vigorous medical management.

Final message

Contrary to popular  perception, tight lesions are  more complex, eccentric , soft and are at immediate risk of ACS.

Non flow limiting lesions remain static in most,  regress in many , still  carries  distinct  risk of progression into full blown ACS , at any time if conditions are favorable.

Fixed concepts and ideas in medical science do not help us  taking medicine forward. Especially so, when these are based on assumptions and approximations. If only we redo these studies with the currently available technology (FFR/OCT/NIR the conclusions would be dramatically different !

Caution : There is no scientific proof  for the above discussion,  of course . . . we lack evidence against it as well !

Reference

2.Glagov S, Weisenberg E, Zarins C, Stankunavicius R, Kolletis G. Compensatory enlargement of human atherosclerotic coronary arteries. N Engl J Med. 1987; 316: 371–375.

3.Fuster V, Lewis A. Conner Memorial Lecture. Mechanisms leading to myocardial infarction: insights from studies of vascular biology. Circulation 1994;90:2126-2146.

4.Ambrose JA, Weinrauch M. Thrombosis in ischemic heart disease. Arch Int Med 1996;156:1382-1394

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An atherosclerotic  plaque is termed  vulnerable when it’s  future behavior is unpredictable .A vulnerable  plaque has a  tendency to get occluded at any time.

Anatomically  a  vulnerable  is  present  , if the lipid core is more , fibrous cap is  thin  and  a  large lipid  core hanging eccentrically. A plaque with high temperature (Hot plaques ,febrile plaques)detected by OCT/Raman spectroscopy or thermography

Note the T cells and macrophages wage a losing battle against a metal monster !

What is the best method to calm down these vulnerable , hot ,inflamed plaques ?

A stent which scaffolds a plaque is believed to stabilse it  and  make it less vulnerable to rupture. This is the most optimistic view on coronary stenting .

Here comes  a pessimistic view !

A metal inside a coronary artery covering is  additional  threat .A metal  is   perennially  thrombogenic  ,especially the drug eluting stents which suppress the normal endothelial  function .

What  is the realistic view  ?

A stent should be used cautiously and judiciously in coronary plaques  with   high risk features  .Here  a  stent  in all probability  converts a vulnerable plaque  into a  relatively stable plaque

When stenting is done indiscriminately( without application of mind )  in stable non flow limiting lesions  stability is replaced with vulnerability.

Is it not curious to know  any angina  in a patient  who  had   PCI  for chronic  stable angina  is labeled  as unstable angina. 

Vulnerable stents

Following are typical  clinical scenarios   where stents could  carry a vulnerability  tag . 

  1. Poorly deployed  stents
  2. Properly deployed (but unnecessarily deployed especially in chronic stable angina )
  3. All Bifurcation stents
  4. Distal left main stents
  5. Stents with plaque prolapse
  6. Finally and most importantly all  drug eluting stents are considered  vulnerable ! (That’s why  our patients has to  live at the mercy of dual platelet blockers , life long.  Of course , there is no life time warranty   that  drugs do their  job properly)

And now . . .  you answer my  question !

Can  stenting convert a stable plaque  into vulnerable plaque ?

  • If  “yes’ is your answer your patients are in safe hands .
  • If  ” No”   is  your  answer ,  you are  fit to become a leading  interventional cardiologist !

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Non invasive imaging of inflamed macrophages  within athersclerosis

The medical  imaging science is  reaching new heights. With most of the  research so far within the anatomical arena we are moving into the  physiologic  and metabolic  imaging. Identifying vulnerable  plaques  within the coronary  artery is a separate field. Most of them are catheter based and invasive investigations.

We  have ben  searching for an  ideal PET scan based metabolic imaging of atherosclerosis. Macrophages are the key elements in an inflamed plaque.

Image Source : Circulation. 2008;117:379-387 .Note the Acttive Macrophages in the Aortic arch area and Coronary ostia

Can we take a photograph of these  inflamed zones   within  the  atherosclerotic plaque  ?

  • It seems we are approaching  that possibility. Every time we screen a person for CAD we can risk stratify on the basis of  percentage inflammation of their coronary artery or aorta .
  • This will complement the CT  or conventional angiogram .
  • If this technology is perfected it can be useful in the evaluation of response to medical interventions .
  • It  could also tel us  the  significance of  raised CRP /cytokines in other wise asymptomatic individuals

PET scan with newer tracers are constantly evolving . One such tracer is  based on copper molecule   64cu-TNP.

Reference

http://jnm.snmjournals.org/cgi/reprint/45/11/1898.pdf

 

 

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Some say medicine is a funny science . . .  it is true  at times. It will remain so , as long as we convert  a fact into a myth and a myth into a fact at our convenience . It  is  often   fueled  by the  whims and fancies of modern research  ! This phenomenon is happening in a regular  fashion  for  many decades now.

The number one killer disease of heart  is  the atherosclerosis  . Atherosclerosis means hardening  of arteries. The advent of coronary  calcium score with CT scans ,  it became a craze among many physicians . (It was   replaced later  by 64 /128 slice MDCT with unprecedented  commercial over tones !)

How can we  conquer the atherosclerosis ?   when the enigma of calcium in coronary artery is yet  to be solved.

The next few decades will be crucial   as  we are  trying to find answer to the following question .

Is  coronary calcium  good ,  bad or neutral   in CAD  ?

This article in American journal article begins the new year 2011  with good news for people , who show some calcium in their plaques.

What makes a plaque vulnerable ?

Plaque contents , it’s distribution and consistency make it vulnerable. Soft spots  formed by   lipids   may  result in  plaque cracks and fissure.   Semi solid  , mixed  ,  gel like soft  plaques   are dangerously prone for  rupture . Oxidation of LDL,  LDL  liquefaction and tissue metalloprotinase , thickness of fibrin caps , all promote softening.  If none of above  mechanism is operative in a given patient , the   plaque becomes  stiff and hard.

Calcification is the ultimate in hardening . Calcified plaque  is resistant to mechanical deformation.If  stiff  plaques   are less vulnerable , hard plaques ( ie calcified  plaques ) must be least  vulnerable . Calcification   can be called an end result of coronary atherosclerosis.

So , calcified  coronary artery  can be referred to as  a failed  mission of  atherosclerosis .It is  equivalent to  death  of atherosclerosis and denotes the end process of this dreaded disease process.

Calcification tames atherosclerosis  in it’s own den

What is the implication of a stiff hard, sharp calcified plaque lining  (or even projecting ) in the coronary lumen ?

As this study has shown , calcium in the walls of coronary artery is innocuous  . Of course , calcium should not be dense and obstruct the blood flow . This will  require  intervention. Many  consider , calcium as  a foreign body in the coronary artery . But the prevalent understanding is ,  presence of non obstructive calcium  is often  a  non issue or in fact a welcome issue in some.

After all , millions of  human beings  happily roam around  with the hardest possible substance  lining their  coronary artery called  stents.

Caution about calcium

This article does not portray calcium as a healing molecule in  CAD . In  the realistic senseit is  too complex to make such a generalization.  The  message is  , calcified lesions are less likely to result in acute coronary  events than soft , non calcified lesions.

It is well known ,  calcium can be problematic for the interventional  cardiologists  .It makes life tough for them in deploying  stents. Calcium rich lesions exerts  radial force in a diagonally opposite direction and interferes with stent approximation.

It is also believed localised , sharp calcium crystals may tear a plaque  and cause   plaque dissections. This  happens if the calcium is lying in an eccentric fashion overhanging the shoulder region of the plaque   abutting a soft spot.

Final message

It is now clear ,  why calcium  score in CT scans  failed miserably to predict  high risk subsets of CAD. In spite of repeated studies  the researchers failed  to show a positive correlation .  The studies are flawed  as they  were trying to look for a positive correlation  which is non existent . In fact , the above study seems to suggest calcium  score may indeed  predict low risk individuals!

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NSTEMI  constitutes a  very heterogeneous population .The cardiac   risk   can vary  between very low to very high .  In contrast ,  STEMI patients  carry  a high risk for  electro mechanical complication including   sudden death .They all need immediate treatment  either with  thrombolysis or PCI to open up the blood vessel  and salvage the myocardium.

The above concept , may  be true in   many situations  ,  but what we fail to recognize   is  that ,   STEMI   also  is  a heterogeneous clinico pathological  with varying risks and outcome !

Let us see briefly ,  why this  is very important  in the management of STEMI

Management of STEMI  has undergone great  change  over the past 50 years and  it is the standing example of evidence based coronary care in the modern era ! The mortality  ,  in the early era was around 30-40% . The advent of coronary care units, defibrillators, reduced the mortality to around 10-15%  in 1960 /70s . Early use of heparin , aspirin   further improved the outcome .The inhospital mortality  was greatly  reduced to a level of  7-8% in the thrombolytic  era. And ,  then  came the interventional approach, namely primary PCI ,  which is now considered the best form of reperfusion when done early by an experienced team.

Inspite of this wealth of evidence   for the   superiority  of PCI  , it is only a fraction of  STEMI patients get  primary PCI   even in some  of the  well equipped centers ( Could be as low as  15 %)

Why ? this paradox

Primary PCI   has   struggled  to establish itself  as a global  therapeutic concept  for STEMI ,   even after   20 years of it’s introduction (PAMI trial)  .  If we  attribute ,  lack of   infrastructure  , expertise are  responsible for this low utility of primary PCI , we are mistaken ! There are so many institutions , at least in developing world ,   reluctant to do primary PCI  for varied reasons.( Affordability , support system , odd hours ,and finally perceived fear of untoward complication !)

Primary PCI may be a great treatment modality , but it comes with a inherent risk related to the procedure.

In fact the early hazard could exceed the potential benefit in many of the low risk STEMI  patients !

All STEMI’s are not  same , so all does not require same treatment !

Common sense and logic would   tell us any medical condition should be risk stratified before applying the management protocol. This will enable  us to avoid applying “high risk  – high benefit”  treatments in low risk patients . It is a great surprise,  the cardiology community has extensively researched to risk stratify NSTEMI/UA   ,  it has  rarely  considered risk stratification of STEMI before  starting the treatment.

In this context , it should  be emphasized  most of the clinical trails on   primary PCI  do not address  the clinical  relevance and the  differential outcomes   in various  subsets of  STEMI .

Consider the following two cases.

Two young men with STEMI  , both present within  3  hours   after  onset of symptoms

  1. ST elevation in V1 -V6 , 1 , AVL   ,  Low blood pressure , with severe  chest pain.
  2. ST elevation in 2 ,3, AVF , hemodynamically stable , with minimal  or no  discomfort .

In the above example,   a  small inferior  MI by a distal RCA occlusion  ,  and a proximal LAD lesion jeopardising entire anterior wall , both  are  categorized as STEMI !

Do you want to advocate same treatment  for both ?  or Will you  risk stratify the STEMI and treat individually ?  (As we do in NSTEMI !)

Current guidelines , would  suggest PCI for both situations. But , logistic ,  and real world experience would clearly favor thrombolysis for the second patient .

Does that mean,  the second patient is getting an inferior modality of treatment ?

Not at all . In fact there is a strong case for PCI being inferior in these patients as the risk of the procedure may far outweigh the benefit especially if it is done on a  random basis  by  not so well experienced cath lab team.

(Note : Streptokinase  or TPA does not  vary it’s action ,  whether given by  an ambulance drive or a staff nurse or even a  cardiologist !  .In contrast ,  the infrastructure and expertise have the  greatest impact on the success and failure  of PCI )

Final message

So , it is argued the world cardiology societies(ACC/ESC etc)  need to risk stratify STEMI (Like we do in NSTEMI ) into low risk, intermediate risk and high risk categories and advice primary PCI only for high risk patients.

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Left main coronary artery disease (LMCAD) often evokes  a panic reaction  among cardiologists .Not every LMD deserve that re. To  label  it as  significant, we have a criteria ,  that is 50% diameter stenosis.  So what you do , for a tapering  or narrowed left main with 40% stenosis. Isolated insignificant left main is rare *, but real incidence is not known.  LMCAD  is  most often due to  , atherosclerosis of left main coronary artery without limiting the flow.

What are the options ?

  • Leave it alone, with intensive medical management assisted by high dose statin(80mg)
  • Elective PCI with stenting , even though the lesion is not significant.

*If associated LAD  or LCX is there decision making is easier .

How  significant is a coronary stenosis ?

The significance of a coronary lesion with reference to “lumen diameter obstruction” is basically flawed. The significance of a coronary stenosis, by tradition is  based on it’s hemodynamic impact ,right from the  CASS days in early seventies.Unfortunately our mind set has not changed even after realising    non obstructive – sub critical lesion is more prone for acute coronary syndrome.  Is it not ironical to call a  40% lesion a non significant one !

So, the  significance of coronary stenosis is two fold.

  1. Hemodynamic  significance
  2. Clinical and  pathologic significance

The former predisposes to often chronic stable angina, later likely to result in ACS.

How will you approach a apparently insignificant left main disease ?

A 40 % lesion in left main is hemodynamically not significant , but pathologically very significant.It needs intensive treatment. Plaque passification with medical approach is first choice.If the lesion morphology is eccentric,  has irregular margins or involves  LAD  or LCX ostium doing a PCI or even a CABG is to be considered in spite of the lesion is  hemodynamically insignificant .

Why , PCI is   considered  “not appropriate”  for   less tighter lesions , even though these lesions  have great clinical significance ?

The answer is simple, The risks  and the  potential cost are more than the benefit !

And further ,  stents are  not innocuous devices  either  , they  always carry a risk of sudden occlusion as like  a sub critical lesion  !

Answer to the title question

True incidence is not known . Our experince (Class 1 c evidence) would suggest Left main disease constitutes up to 10 % of CAD.Among this one third would be hemodynamically insignificant

Suggested reading

Handbook of Left Main Stem Disease


edited by Seung-Jung Park

hbleftmn

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