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Posts Tagged ‘successful thrombolysis’

Nothing in this world is black and white. In fact,  most events are in between . The irony is , our brain  always wants to view  things in two distinct entities !

  • Success or failure
  • Beautiful or ugly
  • Good or bad
  • Win or lose,
  • Rich and poor etc . . . etc

So it is no  surprise !  cardiologists  also travel in the same boat !

They classified  the events after thrombolysis   into two dogmatic categories . Successful  thrombolysis or failed thrombolysis   . . .  as if no other event  can occur in between .

Traditionally 50% regression of ST segment is called successful .   What  about 30%  and 40 % ST regression ?

Further , there is an important caveat  in the timing,  as we  traditionally assess ,  90 minutes of thrombolysis .

Consider the following  situation  :

  1. Thrombolysis  is failed at 90 minutes, but  succeeds  at 120/180  minutes ?
  2. Is 50 % ST regression at 180 minutes is as bad  or as good as 25 % regression at 90 minutes ?
  3. How to label a patient who  is extremely comfortable in spite of ECG criteria of failed thrombolysis ?(Surprisingly this situation is fairly common !)

So, without finding answers to some critical questions , we have defined the success  of thrombolysis with  half baked data .

This is exactly , is the reason we  are unable to do a  valid  study on failed thrombolysis, rescue PCI etc .  We know the results of rescue PCI  ,  always  been  contradictory to the general logic !

It is estimated a substantial number of  STEMI patients following   thrombolysis   fall into a category of partially successful thrombolysis implying partial restoration of blood flow and salvage. The correct definition for  successful thrombolysis and reperfusion should be at the myocardial mass level , and  not at the level of coronary artery.The ECG  is the best available indicator.

Implication for having a  poor definition  of  failed thrombolysis

It is not a rare sight to wheel  in , a patient to a cath lab  with label of failed thrombolysis dangling in his neck  who is clinically  stable  (Has a less than required 50%  ST regression , but a definite, favorable trend with a 30 % ST regression  at 90 minutes  )

How many cardiologists will be willing to abort a CAG/PCI  , as a repeat ECG just  before puncturing  in the  cath lab reveals    successful  thrombolysis ? (little  delayed though !)

If only we have better methods to risk stratify patients following thrombolysis , we can avoid

  • Huge costs incurred
  • Expected and unexpected hazards of doing an emergency  intervention in an adequately salvaged STEMI
  • Hundreds of cardiology man hours can be saved  for better purposes .

Final message

Classifying thrombolyis into  success  or  failure  is a  skewed  way of looking  at this important  issue .

It is an irony ,  cardiologists often  triage LV dysfunction , valve disease , cardiac failure  etc  into 4  grades (  minimal  , mild , moderate or severe  ) . It is  still a mystery ,  why thrombolysis  is never graded  like that ,  and it is always considered as  all or none phenomenon !

There is a substantial number of patients  with partially successful ( or shall we call partially failed !) thrombolyis  .This group must be given adequate attention or inattention  . There  is a urgent need for a through review of how we look at  the post thrombolysis status  . It is better to use the newer imaging modalities like PET/MRI more  liberally to identify  exact sub group  of failed thrombolysis who will benefit form revascularisation .

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Persistent ST elevation is the  general technical term for  failed thrombolysis.Regression of 50%  of admission ST elevation is the required criteria for susccesful thrombolysis .

Thrmobolysis fails in about 40-50% .

Main determinant is the timing of thrombolysis – not the thrombolytic agent ! do not get carried away with all those curent hoopla  about Tenecteplase stuff

If we take 100 patients with persistent ST elavation 90-95 will be in anterior LAD territory .

This is a stunning a cardiology secret no book of cardiology address . . . Implication of which could be very significant . Primary PCI  will always struggle to  prove it’s superiority over thrombolysis  in the right coronary artery .(Note LCX STEMI is different , infact it is more tricky than even even LAD .This issue will be addressed seperately in my blog.)

Read the following link  for  answer to the title question .

How common is persistent ST elevation in inferior leads following STEMI ? https://drsvenkatesan.wordpress.com/2008/09/22/why-thrombolysis-rarely-fails-in-right-coronary-artery/

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Thrombolytic therapy ,  has been  the specific treatment  for STEMI for  many decades. Primary PCI*  is  shown to be  superior  than  thrombolysis  if   performed   early  by an experienced  team in a dedicated facility. (*Conditions apply). It is estimated ,   currently only a  a fraction  STEMI  population get primary PCI (<5%) in ideal conditions . Another fraction , get  primary PCI by inexperienced cardiologists  in low volume centres.

So , thrombolysis   remains, and  would continue to remain ,   the    primary  mode of therapy for STEMI  in the  present and near  future !

How do you assess the successful  thrombolysis ?

It should be recognised ,  there is a fundametal flaw in this  question !

The aim of thrombolytic therapy is  not  to   lyse  the thrombus  , but also  to restore the coronary blood flow to the  myocardium – also called reperfusion . One may wonder , why the term ,  thrombolysis  should ‘t be  used interchangeably with reperfusion. 

A successful thrombolysis  never guarantees  a good reperfusion , for the simple reason ,  distal blood flow in an  obstructed coronary artery  is dependent on ,  many factors  other than relief of obstruction.

Apart from the potency of drug,     other   important factors  that determine  successful  lysis &  reperfusion are  . . .

  • Timing of opening of artery , if the thrombolysis is delayed  ,  the distal myocardium is dead , and   it won’t allow blood flow to enter the mycardium.
  • Microvascular integrity is as vital as epicardial vessels.
  • Distal microvascualture  plugging by the thrombotic debri . This is called”no reflow “

So , we should  primarily assess myocardial reperfusion rather than epicardial thrombolyis ! following thrombolysis .

What are the parameters available to assess successful reperfusion /thrombolyis?

  1. Clinical : Relief from chest  pain. Angina relief  , though subjective is an indication for adequate reperfusion of ischemic myocardium.
  2. ECG-ST segment regression > 50%
  3. Cardiac enzymes: Early flushing of  intra myocytic CPK into systemic circulation and hence early peaking of CPK MB (<1ohours instead of 24h)
  4. Reperfusion arrhythmias(AIVR-Less specific) .Primary VF is now thought to be reperfusion related.
  5. Infract related artery(IRA) patency by coronary angiogram
  6. Distal TIMI flow/ myocardial blush score/ TIMI frame count

ECG ST regression ,  is a direct indicator  myocardial reperfusion   as the ST segment shifts  towards baseline ,  implies  of infarct current of injury . ST regression almost always correlate with good  recovery of LV function  in STEMI .

IRA patency , is an epicardial index , it  does not give information about myocardial blood flow . But ,  a good  distal TIMI flow generally indicates good reperfusion.This  again ,  is  not a fool proof  index,  as even many of the TIMI 3 flow patients  have severely damaged myocardium by echocardiography .

Final message

For the above reasons, one should always  make a distinction between successful lysis and successful reperfusion . Surprisingly ,  ECG  is  the gold standard for assessing successful reperfusion of myocardium ,  while CAG tell us  about epicardial patency and possibly reperfusion also.

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Differential response of thrombolysis between left and right coronary system

  • Thrombolysis is the specific treatment for acute myocardial infarction. ( Privileged few , get primary PCI))
  • Failed thrombolysis occurs in significant number of patients ( 30-40%).
  • Persistent ST elevation  120 minutes after thrombolysis is best indicator of failed thrombolysis.
  • It has been a consistent observation  failed  thromolysis  is more frequent in anterior   or LAD myocardial infarction.

In a simple study we have documented  patients  with inferior MI  rarely had persistent ST elevation and thrombolysis  was   successful in vast majority  of  patients  ( Except in few patients associated lateral MI)

 

The mechanism of better thrombolysis in right coronary artery  is simple.The success of thrombolysis , apart from early time window , is directly correlated with pressure head  and the duration of contact between the thrombolytic agent and the thrombus. In right coronary circulation the  blood flow is continuous ,  occurs  both in systole and diastole that facilitates the maximum delivery of the thrombolytic agent . Further there is a favorable  pressure gradient  across RV myocardium  as the transmural occluding pressure across RV is considerably less then LV myocardium.

This paper was presented in the  “Annual cardiological society of India scientific sessions”

at Chennai, Tamil Nadu.India December 2000

Click to down load PPT full presentation

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