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Posts Tagged ‘tnk tpa’

Which is  the most important factor that determines thrombolysis failure in STEMI  ?

  1. Thrombus load .
  2. Drug efficiency
  3. Time delay
  4. Presence of a mechanical lesion
  5. Hemodynamic instability

Answer : 3 .(Though all 5 factors operate )

Failed thrmbolysis occur in about 40-50% after streptokinase and slightly less with TPA   and TNK-TPA . Delayed arrival and late thrombolysis are  most common cause of failed thrombolysis. As the time flies , the  myocardium gets damaged and the intra coronary  thrombus gets organised .Both these processes make delayed thrombolysis a futile exercise.

               Not all STEMI patients have large thrombus burden. There need to be a critical load of thrombus for thrombolytic to be effective

Some may have a major mechanical lesion in the form of plaque fissure, prolapse and it simply blocks the coronary artery mechanically like a boulder on the road  . The poor  streptokinse  or the rich Tenekteplace !  nothing can move this boulder .The only option here is emergency PCI .

How will you know when the patient  arrives in ER with STEMI whether his/ her coronary artery is blocked with soft thrombus or hard mechanical boulder ?

It is impossible to know.That’s why primary PCI has a huge advantage.  But still thrombolysis is useful as some amount of thrombus will be there in all patients with STEMI.Lysing this will provide at least a  trickle of  blood flow that will jeep the myocardium viable and enable us to take for early PCI.

Final message

The commonest cause for thrombolytic failure is the time of administration and the degree of underlying mechanical lesion  . So  it does not make sense  to blame  streptokinase always !

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Thrombolytic therapy was a  mini revolution  when it was introduced two decades ago .It has since evolved  , not only in the  molecular structure  but also in it’s usage pattern.

The first generation streptokinase is continued to be used even today  . While the latest generation thrombolytic agent TNKTPA(Tenekteplase) is threatening  to push the  old warrior out of  CCU.

(Of course the  American Physician & Pharma  community  never  gave the due respect to  streptokinase  !)

The two common indications  for thrombolytic therapy  are

  • STEMI
  • Acute pulmonary embolism

Uncommon indications

  • Stroke( Can be common in few institutions)
  • Prosthetic valve thrombosis
  • Rarely DVT

From the beginning , there has been a controversy  about the thrombolytic  dosage and  the speed with which it is to be administered .Let us recall , streptokinase was initially  used  in  various regimes ( 5-30lakh units between a 10 -3hr infusion )  Later ,we arrived at a consensus at  15L units  in 1 hr infusion . TPA also experienced the same . Which  settled  for front loaded regimen(35 + 65mg)  . The confusion reappeared when we developed bolus thrombolytic agents( TNKTPA) .

In STEMI thrombus formation  is  often a one time process  while thrombolysis is a continuous process. In pulmonary embolism both  thrombus formation  and lysis  is often continuous process  .

The success of thrombolysis depends on the sustained  drug concentration ,  the pressure at which the drug interacts  the thrombus.

Many times it is prudent to administer  intensive heparin after thrombolysis  to prevent recurrent thrombosis. Further ,  most of the pulmonary embolisms  will require long term anticoagulants.

How to maximize the success of thrombolytic agents ?

  • Local catheter based thrombolysis can be tried  within the coronary ostium (Largely unpopular)
  • Within the pulmonary artery for pulmonary embolism (Still considered an useful option )

It  makes sense , to administer these thrombolytic agents over a prolonged period of time so that the lytic process gets wider recruitment of the natural lytic mechanisms.

When a drug is infused continuously , the drug  reach the thrombus in  a pulsatile manner , which facilitates thrombus dessication  (Like drip irrigation ) . A long acting drug even with a high concentration may not be  very effective , since  the  drug is required to produce a mechanical effect  here . (Unlike say a long acting antibiotics !)

TPA in Pulmonary embolism

The inadequacies  of  2 hour infusion of TPA is  glaring in acute pulmonary embolism .We believe   a 48-72 hour streptokinase infusion   has a definte edge   over a short and brief TPA infusion.

Issues need answer

It is yet , not understood why we can’ t infuse TPA as  a   long term infusion like streptokinase .

Advantage  of bolus TNK TPA  in  pre-hospital phase of STEMI

The argument in favor of bolus dose  thrombolytic agent  is  the ease of administration .

The other the major advantage claimed  is ,  a 10 second  TNK TPA   in STEMI  can  substantially  reduce the time window   and facilitate  early completion of thrombolysis .

Counter point

But , the  later concept is hard to prove  . . .

In fact , there  are  no controlled studies  available for assessing the   efficacy of TNK-TPA   vs  Streptokinase   with reference to various time windows. We presume so many things. An  incomplete   early thrombolysis  may not be better than a  more  successful  but  slightly delayed TIMI3 flow .

As scientists,  when  we try  to answer these  question we  ask for data .  Are we getting it any way ?  Are the existing data reflect  fact ?     We  wonder,  will we may never get   an  hourly  angiographic  data base  about the IRA  patency  in  TPA bolus  vs streptokinase infusion .

It is most unfortunate,   with  many of the critical questions   still to be answered ,  the cardiology community believes ,  they  have  reached the  summit  of  knowledge  about thrombolytic therapy . Current perception is , the research on  existing  thrombolytic drugs  is  deemed to have been complete .

In this hyped  era of interventional coronary  care  ,   it is a remote possibility   to have any  further comparative studies on thrombolytic agents .

The greatest threat faced by  us  today  is the destiny  of  modern medicine is   often  decided in  few corporate board rooms  and   hence   research questions  rarely  emanate from bed side !

In this scenario, where we are not likely to generate   genuine  clinical  data ,  the only way to move   forward is   to go  by  our experience – ” Genuine  experience to be precise . . .”

Final message

Ease of administration should never be the criteria in choosing a thrombolytic agent . It   can severely    compromise the quality of thrombolysis  ! especially in pulmonary embolism and to a certain extent in STEMI.  Success   rarely  comes  with ease  . . .

Many believe , the choice  between  streptokinase   & TPA    goes much beyond it’s academic reasons.  TNK TPA (Tenektepalse) has come in a big way to replace streptokinase  even   in developing countries.  Ofcourse it is backed by a huge study  ! (ASSENT) .

The cost effectiveness and worthiness  of TPA over streptokinase  was  never proved comprehensively.

Note of caution :

The observation made above is   based on personal  opinion  in  about   20 patients  . Readers are  argued to do their own  analysis on this issue and come to a conclusion .

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Failed thrombolysis is an important clinical  issue  in STEMI   as  successful thrombolysis  occurs  only in  about 50-60%  of pateints . The typical criteria to define failed thrombolysis is  the  regression  of less than 50% of sum total( or maximum)  ST elevation in infarct leads.

So what do you do for these patients with failed thrombolysis ?

It depends upon the patient’s symptom, hemodynamic stability, LV dysfunction .

They  should  get one of the following .

  1. Conservative medical management  with /without CAG
  2. Repeat thrombolysis
  3. Rescue PCI
  4. CABG

Medical management is  thought to be  too inferior a  management,  many of the interventional cardiologists  do  not want to talk about . But  , there is  an important  group of patients (Not often addressed in cardiology literature)  who  technically fulfill the criteria  of failed thrombolysis  , but   still  very  comfortable , asymtomatic  and in  class 1. These patients ,  have  a strong option for continuing the conservative management .

Repeat thrombolysis does not have a consistent effect but can  be  tried in some  stable patients. CABG  can be a genuine option in few

Rescue PCI

This terminology  has become  the  glamorous one since the  catchy word  rescue is tagged in the title  itself. For most of the cardiac physicians ,  this has become the default treatment modality.This is an unfortunate perception . What  one should realise   here is  , we are  tying to rescue  the myocardium and  the patient ,   not the patient’s coronary artery !

Opening up a coronary obstruction is not synonymous with rescue .

For rescue PCI ,  to be effective it should be done within the same time window as that for thrombolysis (ie within 6 or at the most  12 hours) .This timing  is  of vital importance  for the simple reason , there will be nothing to rescue after 12 hours as most of the muscle  would be  dead. Reperfusing a dead myocardium has been shown to be hazardous in some ,  as it converts a simple  infarct into a hemorrhagic  infarct.This softens the core of the infarct and  carry a risk of rupture. Further,   doing a complex emergency  PCI  ,  in  a thrombotic milieu with   presumed  long term  benefit ,  is  a  perfect recipe for a potential  disaster.

While the above statement may be seen as pessimistic view , the optimistic cardiologist would vouch for the“Curious  open artery hypothesis” .This theory simply states , whatever be the status  of the distal myocardium ( dead or alive !)   opening an obstruction in the concerened coronary artery  will benefit the patient !

It is  huge surprise , this concept   continues to  be alive even after  repeatedly shot dead by number of very good clinical trials (TOAT, CTO limb of COURAGE etc ).

The REACT study (2004) concluded undisputed benefit of rescue PCI for failed thrombolysis  , only if the rescue was done  within  5-10 hours after the onset of symptoms.The mean time for  pain-to-rescue PCI was 414 minutes (6.5hours)

Final  message

It is fashionable to talk about time window for thrombolyis but not for PCI  .The time window for rescue PCI is an redundant issue  for many  cardiologists ! . But ,  the fact of the matter is ,  it is not . . .

The concept of time window in rescue PCI  , is as important as ,   that of  thrombolysis. Please , think twice or thrice !  if some body suggest you to do a rescue PCI in a stable patient  ,  12hours after the index event .

Important note : This rule   does not (  or need  not  ) apply for patients in cardiogenic shock  or patient ‘s with ongoing iscemia and angina.

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 Rescue thrombolysis in acute   myocardial   Infarction  

 *Venkatesan sangareddi ,Madras medical college,Chennai.India

 

 

   Back ground  Failed thrombolysisin acute myocardial infarction occurs in 30-40% of patients. The incidence of progressive pathological remodelling and cardiac failure is high in these patients. The approach to the patient with failed thrombolysis is generally considered to be catheter based and the outcome is not clear. Bleeding can be troublesome in patients, taken for interventional procedures in the immediate post thrombolytic state. The option of repeat thrombolysis has not been studied widely and is not popular among cardiologists.

Methods:We present our experience with six patients (Age 42-56, M-6, F-0) who were thrombolysed for failed first thrombolysis. All had anterior MI and had received either urokinse or streptokinase (between four to nine hours) after the onset of chest pain. All of them had persistent ST elevation, angina not responsive to maximal doses of IV NTG and beta blockers. The initial thrombolysis was deemed to have failed. Repeat thrombolysis with streptokinase (15 lakhs) was given between 16 and 24 th hour. The clinical outcome following the second thrombolysis was rewarding. It relieved the angina, ST segment elevation came down by 50% and coronary angiogram done at 2-4 weeks showed complete IRA patency in four out of six patients. The factors responsible for failed thrombolysis is complex and multifactorial. A logical explanation from the fundamentals of clinical pharmacology would suggest that a common cause of failure of any drug is due to a inadequate first dose.

Conclusion :We conclude that repeat (Rescue) thrombolysis can be an effective medical intervention for failed thrombolysis in AMI.

Personal perspective                  

                             Repeat  thrombolysis for failed ( initial ) thrombolysis  is still   considered  a  fantasy treatment  by most of the cardiologists !  The utility and efficacy of this modality of  treatment (Rescue thrombolyis ) , will never be known to humanity , as planning  such a  study , in a large population  would  promptly be  called unethical by the modern day cardiologists.

                     While a cathlab based cardiologist  take on the lesion head on with multiple attempts  , it is an irony , poor  thrombolytic agents are given only one shot  and if failed in the first attempt,  it is doomed to be a  failure for ever.Currently,  the incidence of  failed thromolysis could be up to a whooping 50 %  .There has not been much scientific initiative  to enhance the efficacy of these drugs.

                            Common sense and logic would suggest it  is the  inadequate first dose ,  improper delivery , pharmacokinetics is   the major cause of failure of action of  a drug in clinical therapeutics.

If the first  dose is not working ,  always think about another  incremental dose if found safe to administer.

Can we increase the dose of thrombolytic agents  as we like ? Will it not increase the bleeding risk to dangerous levels ?

This is a clinical trial  question.

  • In patients with prosthetic valve thrombosis and acute pulmonary embolism we have safety data of administering of  1 lakh units for an hour for up to 48 hours.

Can  the same regimen be tried in STEMI if the initial thrombolysis has  failed  and emergency intervention is not possible  ?

Logic would say yes . Unfortunately we can’t go with logic alone in medicine .We need scientific data ( with or without logic ! ).But now ,  as we realise common sense is also a integral part of therapeutics  It is called as level 3 evidence / expert consensus by AHA/ACC .

Applying  mind , to all relevant issues ,  continuous streptokinase infusion 1 lakh/hour for 24-48 hours in patients with failed thrombolysis can indeed be an option,  especially when the patient is sinking and  no immediate catheter based intervention  possible .This study question is open to all researchers , and may be tested in a scientific setting if feasible.

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              Intra coronary thrombosis is the sine qua non of acute coronary syndrome ( Both STEMI and NSTEMI.) But thrombolysis is the specific therapy in STEMI and is contraindicated in NSTEMI/UA.

Why is this apparent paradox ? What is basic differnce between UA and AMI ?

In STEMI there is a sudden & total occlusion of a coronary artery usually by a thrombus with or without a plaque .The immediate aim is to open up the blood vessel . Every minute is important as myocardium undergoes  a continuous process ischemic necrosis. So thrombolysis (or more specifically fibrinolysis should be attempted immediately) .The other option is primary angioplasty,  which will not be discussed here.

The thrombus in STEMI  is RBC &  fibrin rich and often called a red clot. Number of fibrinolytic agents like streptokinase, Tissue palsminogen activator,(TPA) Reteplace, Tenekteplace etc have been tested and  form the cornerstone of STEMI management.The untoward effect of stroke  during  thrombolysis  is well recognised , but usully the risk benefit ratio favors thrombolyis in most situations except in very elderly and previous history of stroke or bleeding disorder.

Unstable angina is a  close companion of STEMI . Many times it precedes STEMI often called preinfarction angina. During this phase blood flow in the coronary artery  becomes sluggish gradually,and patients develop  angina at rest .But unlike STEMI there is never a total occlusion and myocardium  is viable but ischemic,  and emergency salvaging of myocardium is not a therapeutic aim but prevention of MI becomes an aim. It is a paradox of sorts ,  even though thrombus is present in  UA ,  It has been learnt by experience thrombolytic agents are not useful in preventing an MI .

 

Why  thrombolysis is not useful in UA ?

1.In unstable angina  mechanical obstruction in the form of plaque fissure/rupture is more common than completely occluding thrombus. So lysis becomes less important.

2. Even if the thrombus is present , it is often intra plaque  or intra lesional and the  luminal  projection of thrombus is reduced  and hence thromolytic agents have limited area to act.

3.Further in UA/NSTEMI since it is a slow and gradual occlusion (Unlike sudden & total occlusion in STEMI) the platelets  get marginalised and trapped within the plaque .Hence in UA  thrombus is predominantly  white  . Often, a central platelet core  is  seen over which fibrin clot may also be  formed.

4.All available  thrombolytic agents act basically as a fibrinolytic agents,  and   so it finds   difficult to lyse the platelet rich clot.There is also a small risk of these agents lysing the fibrin cap and exposing underlying platelet  core and trigger a fresh thrombus.This has been documented in many trials( TIMI 3b to be specific) So if we thrombolyse in UA , there could be a risk of recurrent ACS episodes in the post thrombolytic phase.

5. UA is a semi emergency where  there is no race against time to salvage myocardium .Administering a  stroke prone thrombolytic agent tilts the risk benefit ratio against it.

6. Among UA, there is a significant group of secondary /perioperative UA   due to increased demand situations. Here there is absolutely no role for any thromolytic agents,  the  simple reason is , there is  no thrombus to get lysed. 

7.Many of the UA patient have multivessel CAD and might require surgical revascualarisation directly .

 

So fibrinolytic  agents are contraindicated in UA so what is the next step ?

The emergence of  intensive and aggressive platelet-lytic agents.

A combination of aspirin, clopidogrel, heparin, glycoprotien 2b 3a antagonist formed the major therapeutic protocol in these patients.Even though these are called antiplalet agents some of them  like 2b/3a antagonist eptifibatide, tirofiban, and many times even heparin has a potential to dissolve a thrombus. So technically one can call these agents  as thrombolytic agents.

What are the unresolved issues

                                       Even though clinical trials have convincingly shown thrombolytic agents  have no use in UA .There is a nagging belief  THAT  there could  be group of patients  with UA , still might benefit from thrombolysis as total occlusions have been documented  in some cases with UA.This is  especially true in peri-infarction unstable angina (Pre & post) as there is a fluctuation  between total and subtotal occlusions ) .But bed side recognition of this population is very difficult.

Many would consider this issue as redundant now,  since  most of  these patients  are taken up for emergency revascularisations

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