Posts Tagged ‘edge effect’

Coronary artery lesions can be classified by many types . The popular ones are by Ambrose and Ellis  .They are adopted by ACC and SCAI  .While various  terms  are  used to   describe a lesion. (diffuse, discreet , eccentric , long , tubular  etc) A tandem lesion is the one which has special significance , but is not well discussed in the literature .

A tandem lesion is  diagnosed when  two lesions  closely abut  each other one behind the other  with an  intervening normal segment. (Like the bullets loaded in a  tandem fashion  in a  gun )

Generally there will be at least  few millimeters of normal intervening  coronary segment.This is  referred to  as  connecting segment.

Clinical importance of tandem lesion

Tandem lesions  carry  the  same significance  like  any other lesion. But ,the primary aim is to tackle the two lesions with a single stent. We know stent edges are rheological culprits.  Two stents  have   4 edges. It is better to cover  the tandem lesions with one long stent* even if we have a sufficient  connecting segment.Geographical miss is less likely with a long stent.  In the strict sense one wold require an IVUS (Intra vascular  ultra sound ) to confirm the normality of the connecting segment. Tandem lesion is  a  marker  of diffuse atherosclerosis  and  the connecting segments often   show ectatic changes.

* This is a ironical as  the conventional wisdom would  tell us , lesser the  metal load it is better for our coronary arteries.But once we embark on a complex  intervention we just can’t restrict the use of stents. The more you put the more it will demand.There are some interventional cardiologists who convert the entire coronary artery in to a metal tube (With or without realising the consequences !)

Illusions of  tandem lesion.

Many  times ,  spiral folds  from a single  atherosclerotic   lesion mimics  a double lesion .This need to be differentiated from true tandem lesion.

What is the hemodynamic significance of  tandem lesions ?

Rules of hemodynamics  would  dictate ,  in a linear and laminar flow  model across a tube ,   immediately after an obstruction there will be a significant  drop in resistance.

This  forms the fundamental   phenomenon  within the coronary artery  . This explains the biggest mystery in cardiology . . .  How  the  TIMI flow is  maintained till 90 % of the  lumen is narrowed. This  also  explains the concept of flow limiting lesion .(Why  a coronary lesion do not obstruct the flow  till late stages  ?)

Does this rule on  hemodynamics  apply in tandem lesions ?

When a lesion is followed  by a lesion with little normal segment in between what happens ?

The blood gets a double jolt every time it traverses a tandem lesion. There  may not be sufficient time and anatomy for the mandatory pressure drop to occur. So for a  given degree of obstruction ,  tandem lesions  is likely to be   more thermodynamically significant than a single lesion.

Pressure recovery after  an obstruction is also incomplete , as the forward head of blood column encounters another hurdle even before it recovers from the initial turbulence.

Which lesion is more important   in tandem proximal  or  distal  ?

The distal lesion determines the thermodynamics of proximal lesion while the distal lesion as  such is  less influenced by proximal.

Long lesion vs tandem lesions

Some times it may appear ,  it is better to have a long lesion than  a two lesion  in tandem. This is because the stent will approximate more evenly .Further there is less likely hood of in -stent restenosis in long lesions as the   edge effect can occur  right in the middle of  the stent in tandem lesions .

Now it is increasingly realised, many of the sub acute thrombosis  are due to po0r stent approximation in tandem lesions or long lesion.



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Coronary stents have revolutionised the management of CAD. Stents are metallic scaffolding devices that help keep the atherosclerotic plaque  plastered within the coronary arterial wall.Thus it gained the name angioplasty. Stents have aradial strength that  exerts a constant force on  the plaque . Since metals are unfriendly partners for coronary artery , we need to have minimum metal within the coronary artery.The stent struts weave around the lumen generally the stento/ artery area ratio should be as less as possible (15%).

But this has a trade off .The uncovered area of plaque tend to project into the lumen .This is many times not significant.But can be a problem if the plaque is very soft and bulk of the lipid core may reenter the lumen.this event is called plaque prolapse.


What is the time taken for plaque to prolapse ?

Generally it is late event.But it can happen immediately after the procedure also.

Which type of lesions are more likely to have plaque prolapse ?

Eccentric and complex lesions especially with overhanging edges are prone for prolapse

What is the sequale ?

It can be benign.If there is a erosion due to stent struts can precipitate an ACS.It progresses into instent restnosis in many.

What is the angiographic appearnce ?

Angiographically it often appears as luminal  irregularity withi stented segment .

Many times , it may appear as a filling defect also.

Is there any specific issues in plaque prolapse in drug eluting stents ?

Coornary artery is not drugged uniformly by the drug eluting stents.In fact contact  lines of metalic struts  , through it’s micropore oozes the drug with polymer.Pathological studies have revelaed non homogenous drug penetration and resultant irregularity on the plaque surface.This could amplify the plaque penetration preferentially in few areas.

How to manage plaque prolapse ?

It should be managed as any other instent restenosis.Plaque resection with atherectomy devices has not solved the problem to the desired levels.A second stent is the most common approach advocated by the cardiologists.(Whic is not ideal though !)

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