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%)
Shaft : Mid, distal or diffuse Left main
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 . . .
Incomplete occlusion of single LIMA graft
Occlusion of SVG-LCX and patent LAD-LIMA
Occlusion of LIMA- LAD graft but patent SVG-LCX graft
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 .
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 .