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Posts Tagged ‘geographical miss’

Self expanding stents during primary PCI : A perfect solution for optimal stent apposition ?

Posted in Cardiology -Interventional -PCI, cardiology -Therapeutics, cardiology- coronary care, Cardiology-Coronary artery disese, tagged , , , , , , on September 21, 2011| Leave a Comment »

During   primary PCI , the weakest link  for a  cardiologist  is  , he is never sure whether  the  metal jacket  has covered the entire  disease segment with optimal apposition .  (Geographical miss is another issue !)

This is because  , even though the inflation pressure is  uniform  within the balloon ,  the required  apposition pressure is not the same .This is obvious as the lesion surface has a varying consistency and uneven surfaces . It is a  huge guess to quantitate the relative  contribution of thrombus and plaque  within  the 100 % occlusion  that has resulted in the STEMI. Hence  some areas may get over apposed and others lesser apposed. Further , the stent -vessel wall interface  in all likely hood enclose a   layer  of clot .This is almost certain  during complex primary PCI. One can imagine the sequel if this thrombus layer dissolves later ! (Edentulous stent )

It is surprising , why cardiologists has  so far not  thought  of a  self expanding stent  which  can snugly appose the vessel wall in this setting  . The   radial strength   from the  stored potential energy can be used up future use. This is most important  in first few days following STEMI  , when the coronary arterial lumen can vary depending  upon the

  • Vasomotor  tone .
  • presence of thrombus
  • Plaque   ploughing /milking  effect
  • Vascular remodeling

Cardiologists  deploy a stent  based on the morphology  on day zero of STEMI  .This may be  totally irrelevant  , since after a  few days    the lesion may change its morphology ,  thrombus may migrate , vascular  dimension may change. In such a  situation*  , a self expanding stent can tackle these issues very effectively by constantly adjusting  and fine tuning the luminal  diameter and  the apposition pressure . It  does not give any chance  for  thrombus to form  between the vessel wall and stent .

Here is a study that gives fresh insights regarding the role of self expanding stents during STEMI .

Note the “Auto adjusting”  of stent diameter  in the first few days after  the stent deployment, depending upon the luminal needs !

Animation

http://www.stentys.com/file_bdd/annexes/1284135580_video_stentys_en.swf

* Logically  during  primary PCI for  STEMI  ,  POBA and thrombus suction  may be the best option in many as all stent related complication is instantly eliminated .But it is a battered concept ,  most of the current day cardiologists would feel guilty to come out of  the cath lab  without a stent  in  primary PCI scenario  !

Final message

Self  expanding stents during primary PCI :  Is it a  perfect solution  for optimal stent apposition  ?

It seems so  . . . but  the track record of current cardiology devices never fulfilled the initial promises !

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What is geographic miss during PCI ? How do you classify it ?

Posted in Cardiology - Clinical, Cardiology -Interventional -PCI, cardiology -Therapeutics, tagged , , , on August 22, 2011|

A stent missing a  lesion after a PCI  is referred to as geographical miss.

It can be metal missing a lesion ( in BMS )or a drug missing a lesion  with DES.

Geographical miss is  obviously  more important with DES ,   as both metal and drug can miss a lesion ! (A double miss !)

Read a related article in this site. Geographical Miss : Difficult coronary Runways . . .

What are the types of  geographical miss ?

A.Longitudinal

B.Axial

Longitudinal miss is more of a technical failure (Interventionist error ) While  axial miss  is  often a  design or concept failure .

Longitudinal  miss results in edge lesions ( either  stent inflow or outflow lesions) .Axial miss result in discreet  in-stent lesions .

Please remember ,  axial GM  is  much more common .

What is definition of  axial geographical miss ?

Inadequate inhibition of intimal hyperplasia within the region of stent .

Mechanisms of  geographic miss in DES era

  1. Stent  vessel diameter mismatch  (Less drug vessel contact)
  2. Low drug dose -Pharmacological error
  3. Stent radial strength more than the desired force per unit area . This excess  stress  effect  might interfere with drug release.
  4. Some degree of vessel injury is needed for drugs to percolate. (A very smooth deployment may not release the drug  properly )*

*A modern day cardiologist  is expected not only to deploy the stent properly , he has to make sure drugs reach the target cells . What an  irony  cardiology can be  .  . . a  too gentle  PCI  can show up a  negative face ! when we want to poison selectively  the atherosclerotic plaques .

What is the incidence of GM ?

In  STLLR trial which looked specifically the issue of GM  the incidence was very high ,  an astonishing 65 %

How to recognise it ?

Longitudinal miss can be identified by conventional angiography.

Axial miss is very difficult to diagnose . IVUS,ICT will  help.

Many times it is an after thought  when patient presents with  an event.

What can we do once we recognise it ?

Unfortunately nothing much can be done to reverse the miss especially the axial ones.

longitudinal miss can be corrected by a over lapping stent .(Still ,  we do not know the implication of double metal doses  dragging an edge of lesion !)

Can  “Geographic miss”   be termed as  a failed PCI ?

Clinically , technically , logically and morally  Yes .

But  practically  “No” ,  as GM  takes much longer time to manifest as a clinical event  ,  by then , no one   would  really attribute  the event as  procedure  related  . And of course ,  we have numerous other  excuses to convince our patients.

The link to STLLR  trial which gave us the startling data about GM .


http://www.ajconline.org/article/S0002-9149%2808%2900350-0/abstract

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Geographical miss : Difficult coronary “Run ways” and turbulent stent landing !

Posted in Cardiology - Clinical, Cardiology -Interventional -PCI, tagged , , , , , , , on July 21, 2011| Leave a Comment »

Landing an aircraft is a high precision job. A pilot and co pilot with the help of air traffic control  must  do this job meticulously every time .They   are not  afford to make any mistake .Number of lives are at stake.

In cath lab something similar happens every day  although a single life is at stake !   We call this coronary stent landing  . If  it lands  wrongly  it is referred to as  geographical miss ,  a descriptive  terminology for a poorly deployed coronary stent !  ( In strict terms it  should be called as  failed PCI !)

But there are few vital differences   between the two . . .

If an aircraft overshoots  the  runway   it is visible to every body and it becomes a national news next day !

If you deploy a stent away from a lesion it is usually a  silent  event  . Only a few alert fellows and staffs know it ! Patient  often gets discharged  next day (of course after paying the bills )  and  the consequence is often delayed  by weeks  or months  when he comes back knocking  the  ER doors with an ACS !

Final message

The stent -plaque  dissociation is  much more common than we perceive ,  for the simple reason cardiologists have  learnt  to accept   luminal shadows  as surrogate markers for plaques . ( Coronary blindness !)

It is imperative to  apply all our senses properly  in the cath lab ,  like  our  pilots  do while they land  . Be prepared  for  turbulent weather which  is common in cath lab as well !

http://www.sciencedirect.com/science/article/pii/S0735109701011123

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Pre-stenotic dilatation : Why do the coronary artery dilate proximal to an occlusion ? What is the clinical significance ?

Posted in Cardiology - Clinical, Cardiology -Interventional -PCI, cardiology -Therapeutics, Cardiology -unresolved questions, cardiology- coronary care, Cardiology-Coronary artery disese, tagged , , , , , , , on July 10, 2011| Leave a Comment »

Laws of fluid dynamics dictate there is a pressure drop across   a point of narrowing  and recovery  thereafter  . At  recovery point if the vessel wall is weak it tends to balloon out .This is called post- stenotic dilatation .This is  the anatomical equivalent of Bernoulli or venturi  effect. This theoretically  occur only distal to obstruction .

How do you explain the common observation of pre- stenotic dilatation?

  • Intimal weakening due to disease process is the prime  suspect.
  • Pre stenotic  increment in mean pressure  also play a role .
  • Mechanical distention due to stagnated blood  proximal to  critical obstruction  is  a  logical explanation.
  • Finally and most importantly ,contagious , sub – angiographic  atherosclerosis.

How is  dilatation  different from ectasia ?

May be they are all related phenomenon. The definitions  of ectasia ,  dilatation, aneurysm are  more to do  with semantics than with academics.

Clinical and hemodynamic implication in cath lab

  • Sluggish  flow prone for thrombus
  • Stent selection errors likely
  • Stent dislodgment  and migration

Long term effects

  • In stent re-stenosis is more common if adjacent segment show dilatation.

Finale

Enlargement of vessel wall in both pre and post stenotic segments are possible . In small vessels pre- stenotic dilatation is  more common , while in large vessels post stenotic dilatation is  more prevalent .(Aorta, Pulmonary artery)  The mechanisms are slightly different. Apart from the lesion tightness ,  hemodynamic  and genetic factors are also responsible These dilatations are  often labeled as ectasia in coronary artery  and  most cardiologists  tend to   ignore this finding especially if  the margins are smooth.

But , newer imaging modalities like IVUS, OCT have given   better  insight about these dilatations.These   are  actually an  expression  of the  contagious  atherosclerosis .  Pre-  stenotic segments are prone for extensive disease  than even the diseased segment due to  more hemodynamic turbulence. There is some evidence atherosclerosis progresses  proximally more than distally.Smooth margins within the  pre -stenotic dilatation  does  not guarantee  disease free status.

During PCI  there could be  an  argument for covering the dilated  pre- and post stenotic segments  as well* . (We vouch for endovascular stenting when aorta is dilated why  do we hesitate  in coronary  ?)  .Careful selection of  coronary stent size  is  recommended  and  allowance should be given  for these two (Pre and post coronary dilatation ) patho -anatomic phenomenon.

* Stent missing a lesion is stylishly called geographical  miss ! This should logically include dilated segments also.

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A brief lecture on tandem coronary lesions!

Posted in Uncategorized, tagged , , , , , on February 23, 2011| 1 Comment »

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.


http://www.springerlink.com/content/g063752436617n51/

http://www.ncbi.nlm.nih.gov/pubmed/8789675

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What is plaque prolpase within a coronary artery ?

Posted in Cardiology - Clinical, Cardiology -Interventional -PCI, Infrequently asked questions in cardiology (iFAQs), tagged , , , , , , , , , , , , , , , , , , on March 20, 2009| Leave a Comment »


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.

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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