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Posts Tagged ‘coronary angiogram’

Note :This is a copy of  my earlier blog on coronary micro-circulation  published few years ago.Recently this got numerous hits .Hence I have just reposted it with slight modification.

Human coronary circulation stands unique among  others as it is a  life-sustaining circulation.It is indeed a great medical achievement  to visualise  the right and left coronary artery  system by coronary angiogram.  Actually,  what we see is  only a fraction  of  the surface area of coronary circulation .The surface area of  epicardial coronary arteries   constitutes  less than 5 % of entire coronary vascular tree .

And  . . .

An in vitro heart with special catheters showing the true extent of coronary circulation: Courtesy http://eurheartj.oxfordjournals.org/content/28/3/278.full.pdf+html

This  is the reason  normal coronary angiogram can never mean normal  coronary circulation !

This huge gap in our perception is the single important factor  that  explains the vagaries  of modern coronary care .

This also make any clinical coronary  scenario  a  reality .

“A patient with normal coronary angiogram getting a myocardial infarction , the next day and a severe triple vessel disease living comfortably  for  decades with medical management”

So , it is essentially a  false  sense of  scientific accomplishment  by the cardiac scientists  at  least in the  of coronary circulatory physiology.

What determines the extent of these invisible coronary micro circulation ?

There are innumerable channels of micro vessels traversing across the heart, sharing , bridging , branching, penetrating  and  perfusing the muscle mass.They can be anatomically patent , physiologically non patent .They can be recruited by hemodynamic stress .These are never visualized by current imaging modalities..It is also influenzed by  favorable growth milieu and hormonal and neural stimuli.

Ignorance based cardiology

What is the mechanism  of primary VF following acute STEMI ?

The quantum of  coronary micro circulation is like the vast  cerebral neuronal net work .We have every reasons to believe they are have unique genetic imprint.How else you can explain a man with full blown STEMI come 24 hours later comfortably to the OPD while another loses his life with a stormy primary VF before even boarding the ambulance !

Why many cardiologists   do not give due credit  the   coronary collateral  circulation  ?

Right from the days  of  Levine in 1970s( Who made a seminal contribution  about coronary collateral)  the  utility value of  coronary  collateral  circulation  was never able to convince the cardiology professionals .

It has been our traditional  teaching ( without much evidence of course  !) coronary collateral circulation  is not effective to support blood flow during exercise . This fact has been  disproved  many times . Coronary collateral circulation was indeed useful in limiting damage in ACS and  relieve symptoms in stable angina.It helps  in reverse remodeling and provided electrical stabilty as well in post MI population.

Still , the concept  was  alienated  and   made   totally irrelevant  in the interventional  era  . Many   cardiologists  found well-developed collateral’s as an interference to their expertise and ego since it has a potential to alter the indication of PCI.They  continue to have  strong  scientific conviction (Pseudo ?)   that man made collaterals must always been superior to God made collaterals !

Whenever  some credible  reports emerge about  collateral circulation   being   equivalent to  revascularisation procedure , these concepts were  prematurely buried for some reason.

In the last decade there was a concern  about  performing  PCI in patients with well-developed collaterals  .The argument was , they tend to develop early stent occlusion and restenosis . It  was a genuine  query  raised by few thought leaders in the field as  collateralised vessels  suffer from  low flow   after PCI ,   if the pre -existing collateral continue to function.

But  then , few  studies countered this , and PCI was shown to be safe and  in fact may  fare well   in  patients  with  extensive collaterals .

In these  studies  interventionist’s  argument looked  amusing !  as they  seem to  define a  successful  PCI  as  not only to open the occluded vessel  but also  make sure to close  all functioning  collaterals  .(What a  a pity for our natural biological  angiogenic forces which had  worked  and  grown meticulously for months!)

Cardiac science in the current format,  makes   the future look  bleak for coronary a collateral circulation .With  early PCI  becoming a norm we will never ever allow the natural collaterals to  grow  ,  and even the  established collaterals  will have to face a stiff   fight  for survival  with  sophisticated coronary interventions .

Competing interest in the filed of  coronary collateral   research

While the basic scientists want  to  grow collaterals with angiogenesis ,  stem cells etc  interventionists   continue to  indulge in rampant angioplasties which  will suppress  collateral growth.

This implies we will struggle to  establish  the true  importance of  coronary collateral circulation .

Final message

Can it be an  effective form of revascularisation  ? 

My personal  inference  is   coronary collateral  circulation  “would and should”  have  a definite role  in at- least  some of the subsets  with chronic coronary  syndromes. If we think otherwise . . .    it’s against the principle of  natural biological science .

A good  collateral   system with optimal medical management  can save not only our  patient’s  lives but also  their hard earned currencies !

Reference

Here is a rare article in European heart   journal that discuses coronary collateral circulation  . Let us welcome such wonderful  reviews which keep the interest alive on the filed.

http://eurheartj.oxfordjournals.org/content/28/3/278.full.pdf+html

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This is an  RCA of   a  patient who had chronic stable angina  , class 2  with moderate anti anginal medication.

What shall we do ?

  1. The RCA needs  multiple stenting
  2. Multiple plain balloon angioplasty
  3. CABG to PDA
  4. No intervention ?
  5. It depends upon status of LAD  and LCX

The correct response would be 5

Without knowing  the status LAD and LCX . . .  RCA should not be touched . Further,  the concept of tackling  the  coronary artery  by itself  is   fundamentally wrong !  We are supposed to tackle patient’s symptom ,   reduce future risk of  events and   not merely  their coronary artey !

His LAD and LCX was near normal. In the weekly  cath   meet   PCI to mid RCA  covering  the critical segment was  strongly debated but  lost a close race .

The final decision was to allow the patient to continue   intensified   medical management (Statin 80mg /Metoprolol 100mg ) . He is comfortable with that .

Medical management  in a tight  single vessel disease  can never be digested by  any   Interventional cardiologist  whatever   may be  the guidelines !

Final  message

Do not decide PCI on the basis of   how ugly a coronary artery looks , rather spend some time on true  symptomatology ,  optimise baseline therapy  and re assess risk profile

One learned dictum is ,  do not  meddle a RCA ,  however severe the lesion may be   if  LAD and LCX are fine.*

*This  rule is not applicable in ACS

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In this politically and scientifically  uncertain world nothing is  in black and white. How can you  expect  EST to behave differently ?

Even as  we  are fully  aware of the  limitations  of EST  ,  it  does not make sense   to categorize  EST result into either positive or negative .

In fact , our  estimate suggests  a significant bulk of the patient would fall in the grey zone  .

It is referred  in various terms by  the reporters of EST .

  • Borderline positive
  • Mildly positive
  • Equivocal
  • Inconclusive

What does all these terms mean to the patient ?

It mans only one thing . . .

Physician  who reports  the  EST    is unable to  conclude whether  his patient has  significant  CAD  or not . It is a dignified way of  expressing  the  limitations .

Many factors may play a role. (See the illustration above )

  • Patient factors : Poor exercise stress levels and conditioning
  • Lesion factors:  Collateralised CAD, treated CAD  can result in partial or mild  changes.
  • Machine factors :Caliberation errors.
  • Interpreter : (Physician ) factors

Error in measurement of ST segment . What is borderline  for  one doctor may indeed be true positive  for the other and vice versa .

How will be the  EST in  a  revascularised  or  medically treated CAD ?

If revascularization is a complete success ,  stress test  would  revert back to normal or it can be a borderline as we have just mentioned.

To our  surprise ,  it may  remain  positive in spite of apparently successful procedure.(Residual wall motion defects , scar mediated  ?)

How to proceed  after this borderline EST/TMT ?

Few options are available for the physician/patient

Talk  with the patient again  , assess the  baseline risk  of CAD   if it is low ignore the TMT result and reassure.

  • Repeat  stress test after  a month.
  • Stress thallium
  • Doubutamine  stress
  • CT angiogram
  • Regular Cath  angiogram* (May be the best , of course it also carries a  risk of labeling  the condition as  mild  CAD / non critical CAD etc )

For the  patient  the  easiest  option  may be ,   self  referral to a different cardiologist .   (Also called second opinion )

Final message

There is indeed an entity called   borderline  EST  . Do not dare to  ignore it  or else  face the consequences .

Read  related articles in this site .

1.Can medical management convert EST positive to negative ?

2. Should every one with positive EST should undergo CAG ?

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Very often in clinical  practice  cardiologists are asked to R/O significant coronary artery disease in asymptomatic persons .This population includes  people with multiple risk factors like diabetes, HT dyslipidemia  and non specific ST/T changes in ECG.

Many of us have lost the confidence of   ruling out CAD   in these population without looking at their  coronary angiogram.

Is it a right way of practicing cardiology ?

What we need to realise is,  we are asked  to rule out any critical lesions that are going to make a impact on these  other wise comfortable patients.  Nothing wrong if you miss a 30% lesion in PDA or OMs or diagonals !

Can we do this without doing coronary angiogram ?

Yes ,  we can .

Step by step  Ask these questions

  1. Ask the patient , if  he /she   can climb three  flight of  stairs  without any difficulty or
  2. Walk briskly for  20 minutes (5km/hr)

If yes , give  a   certificate   that he  has no critical  left main or proximal LAD  disease.

If you do not believe in his words , put him on a tread mill ,  if he crosses   stage  3   Bruce in TMT ( 9 mts)

give the above certificate  “with a frame”  now .

For still suspicious  physicians ,  We have  one more  investigation called  echocardiography !

Echo : The forgotten tool  for screening left main lesion.

Modern day echo machines have a  3mm resolution power (Many have 2mm ) .While ,  we are expected to look for 3mm vegetation to R/O Infective endocarditis , rarely is  a  cardiologist ,  tuned to  look for the left main ostium  in routine echocardiography  which averages 4-5mm is size. (Left main by echo link to another article)

In short axis  view just tilt at the level of pulmonary valves  (Atrio- pulmonary sulcus) one can visualise the left main ostium and the proximal left main emerging from the 4 o clock position. If you are lucky you can see the entire left main.

If nothing satisfies the physician (Or the patient)  ,Refer him for sliced CT scan , catheter coronary angiogram , or a  nuclear Imaging .Be ready for the attendant anxiety, interpretation errors, corporate  pressures , urge to  balloon ,  kick backs etc etc

By the way , how can  one  be happy by ruling out only left main disease ?  Is it not other lesions possible ?

Experience (Not science) has taught us  no  critical coronary obstruction is  possible ,  if  a patient walks for  9 minutes  in treadmill (10METS).

Even if it is there (A remote chance)  there is little documented benefit of any revascularisation procedure.

Counter point ?

Is it not a “crazy idea  to rely on patients history in ruling out  CAD   in these era , where   angiograms relayed  live  into   cardiologists  ipad  ?

Science has no value if it is not applied  for the patients welfare. Meticulous clinical  examination (And application of mind)  is the foundation stone on which  any medical investigation and therapy  should be based  upon. Most of the inappropriate coronary revascularisation are due to  neglect   of  this vital  component of clinical examination.

(I wonder ,  is it  really possible  these ” acts of omission”   be  deliberate some times  ! )

Final message

Clinical interrogation  may  miss an insignificant  CAD  ,  but it can never miss a critical CAD* .

 

Do not do coronary angiogram routinely to R/O  CAD.

It is not the way cardiology is to be practiced !

If only we apply  those  simple,  time tested concepts in every day practice we not only  save millions of  Rupees ,   but also thousands of futile   diagnostic tests and associated untoward effects can be avoided.

* Senstivity of  ruling out any CAD is about 70% , but it’s capcity to R/O critical CAD approaches 100%.

Reference:

Please refer your own Brain.

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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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Newtons third law of motion  says for every  action  there is  an equal and opposite  reaction .

In vascular hemodynamics  whenever there is a an obstruction , there tend to be a dilatation of   the same blood vessel  somewhere distally.

It may not be linked to newtons law but it is  observed in many .It is more common in large vessels than small ones.

Here is a patient with a tight LAD lesion with a significantly  dilated segment located immediately beyond the  obstruction.This can be considered as a post stenotic dilatation. Coronary ectasia is  also a  possibility but since it is related to site of obstruction the former is likely .


What determines the post stenotic dilatation ?

The exact mechanism is not clear. There is  a definite ,sudden  pressure drop distal to  the  obstruction. This  pressure drop  recovers beyond a certain distance . At this point ,  the rate of increment in  velocity of   peaks .This somehow has an effect on the  distending  pressure  and the adjacent vessel wall gets radially stressed and begins to dilate. (Opposite of what is expected in Bernoulli effect ?)

Is there a anatomical defect in  post stenotic dilatation ?

Not every  one goes for post stenotic dilatation.There is a possibility it occurs only in genetically susceptible individuals .

Significance in  interventional cardiology

The post stenotic segment has a potential to misbehave in the period following  PCI . If the distal instent stenosis  occur (even if it is minor ! ) it can induce a cycle of post stenotic eversion of normal segment and risk of edge effect or stent thrombosis is more.

Read also Glagovian phenomenon – A form of  intra stenotic coronary artery dilatation

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