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What is protected left main disease ? How good is the protection ? If good , why should it need another protection ?

Posted Sep 15 2009 10:22pm

Left main disease  is an important subset of CAD , and it has special interest for the interventionist. Traditionally cardiologist have   a fear to touch this lesion , as they thought a sudden occlusion within this vessel is life threatening   . Later on as  they gained experience  it was thought  we could intervene safely at least in protected left main . Subsequently  it was realised this fear was largely unfounded  , after all  the proximal LAD is equally  dangerous and we spend hours together inside an LAD ! .Now we have technology and expertise to do successful PCI any where in LM. And  unfortunately , the same expertise is not applied in selecting the ideal patients who will benefit the most . LMD has become a glorified indication for PCI.

The terminology of protected and unprotected LMD is in vogue for many years . Unfortunately it do not convey a uniform meaning . In next few minutes ,  I shall share  my views on the nuances of protected and unprotected LMD .

The term   protected was  not  coined by  cardiovascular physiologists   but by   interventional  cardiologists . Hence it connotes a  anatomical  meaning rather than physiological.  Protected LMD  meant there must be a at least one  graft to either LAD or circumflex . And this graft should be functional. The presence of this graft is supposed to increase the comfort levels of the interventionist as well as  the patient.

A left main coronary artery disease angiographically  can be  classified  as

Common types of Left main lesion

  • Asymptomatic , non flow limiting , angiographically insignificant disease(< than50%)
  • Ostial
  • Ostio proximal
  • Shaft : Mid, distal or diffuse Left main
  • Bifurcation

Unprotected left main

  • All the above lesions
  • Non functional GABG grafts ( eg: LIMA occlusion makes LAD unprotected)

Protected left main

  • Post CABG  with atleast one functional graft to LAD /LCX
  • ? Left main   with total  LAD and very good LAD collaterals from RCA /LCX

Partially protected Leftmain

It could mean any of the following,     Left main Plus  .  . .

  1. Incomplete occlusion of single  LIMA graft
  2. Occlusion of  SVG-LCX and patent LAD-LIMA
  3. Occlusion of LIMA-  LAD graft but patent SVG-LCX  graft
  4. Patent LIMA-LAD  but a  critical  LM / LCX  bifurcation lesion with no grafts for LCX*

The above 3  situations may demand a  PCI .But logic would  suggest one would try to open up the partially occluded graft rather than open the left main . Of course the decision involves status of RCA .

*The only indication for a  PCI  in protected  LMD could be 4

Unusual ( Crazy !) questions  about  left main disease

Can left main be protected by collateral circulation ?

It is very common to find Left main   bifurcation  lesion   with LAD having  very good collaterals from RCA sometimes filling up to proximal  LAD .This can be considered   “protected left main equivalent”

As on today , cardiologists would rather   believe  a surgeon’s graft  rather than a naturally grown  collateral from RCA however extensive it may be !

But logics and real case experience would indicate in a patient  with LMD and an  extensively collateralised LAD can in fact be  considered a protected left main.

If a  left main is well protected by a functional LAD graft , why should we do a PCI for left main at all ?

This question was risen in one of our cath conferences , a patient   who had functioning  LIMA to  LAD graft.His   RCA had a functioning  venous graft  and his circumflex had a partially functioning  graft.The left main had a near total  obstruction and the proximal  LAD was  faintly visible .

Since the  patient  had class  2 angina Options were discussed .He  satisfied  the  current criteria of protected LMD .Just because he fulfils the criteria of protected left main , he  does not  become eligible for  left main    PCI .  After all he is having this LMD for many years. Protecting again the left main which is already protected is not a big deal in terms  of outcome .  Double protection is waste of resource at additional risk. It was decided to attempt a PCI to SVG graft to LCX. If it does n’t work leave him with medical management.

Does  every patient  after a CABG   has a high chances of developing LMD ?

What is accelerated atherosclerosis of Left main following LAD /LCX  grafts ? It is  true  left main  has high risk of  accelerated atherosclerosis and it   undergoes  gradual obstruction once the LAD and LCX is grafted.This is due to low flow across the native left main as distal grafts maintain the flow . This is all the more likely in good bulk of patients who had undergone  CABG  where   LMD  was the indication .

A typical scenario

A left main patient   who undergoes a CABG  a follow up for a suspected  angina  angio after 5 years show the  totally  or near totally occluded native left main . Sudden   Visualisation of worsened leftmain disease    makes this patient eligible for  a  PCI as he fulfills the criteria for  protected leftmain .

Final message

A well protected left main  with a good  functioning graft especially to LAD   most often do not require a fresh revascularisation  procedure  irrespective of the tightness of left main disease . Most of such patients will be candidates for medical therapy . Contrary   to the popular belief ,   left main  intervention   could  be    confined  to   ” unprotected LMD   rather than well protected LMD” as the  potential benefits are more .Further interventional resources need not be wasted in giving second alternate protective channel  for an already protected vessel !

Of  course it should be remembered  in any given patient  with  protected or unprotected  LMD  the indication for  revascualrisation  is based on  the severity of lesion , symptoms,  LV function ,  residual ischemia, viability  etc .

Suggestions  , comments  and  corrections  welcome

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