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Posts Tagged ‘thrombolysis’

Thrombus formation  and subsequent lysis  either spontaneous or pharmacological is the key events in acute vascular emergencies .We know both STEMI and acute strokes can get aborted  naturally.

The thrombus which initially forms , triggers a natural lytic mechanism and this fights vigorously against the clotting process , and tries to get rid  of the intravascular clot.

The early  minutes are vital. (Like the T 20 cricket )  the win or loss is decided in the first few overs . The mantra is unrelented attack of the ball . . .ie thrombus !  In some patients  the clot  can never grow big to fill the lumen.These are lucky few .The mechanisms are common in both cerebral and coronary circulation. Here is were comes the role of antiplatelet agesnt .An aspirin or clopidogrel administered within minutes can prevent the genesis of  central core of the thrombus .(This is the  secret of aspirin scoring over stretokinase in STEMI in ISIS2 study done three deaceds ago !)

It should be realised,  our understanding about spontaneous lysis is very little considering explosive growth of other aspects of cardiology. It is mediated by circulating  TPA and antithrombin 3  .  Remember  every humans have it in their  blood .But how much ? How to augment it ‘s power at times of thrombotic crises ?

What could be the clinical correlates of spontaneous thrombolysis ?

  1. In brain classically it is TIA .
  2. In heart do we have TIA equivalents ?  .Yes it transient rest angina

Link to video on TIA of the heart

Read this article to get a glimpse of  natural cerebral thrombolysis  and shall we   extrapolate it to coronary spontaneous thrombolysis  .Why not ?

Arch Neurol — Nonocclusion and Spontaneous Recanalization Rates in Acute Ischemic Stroke: A Review of Cerebral Angiography Studies, December 2002, Kassem-Moussa and Graffagnino 59 (12): 1870

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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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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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Conduction disturbance is a fairly common occurrence following  MI. Inferior STEMI is especially prone for AV blocks. This is because  the  blood supply to AV nodal  tissues and the inferoposterior surface of the heart  share the same arterial territory . AV node gets it supply  90% of time by right coronary artery(RCA )  and 10% by  LCX. Very rarely from both .

The common bradyarrhytmias that we encounter in inferior MI are

Sinus bradycardia

Sinus pauses ,SA blocks

AV blocks

Functional

Vagotonic

Organic

Ischemic

Necrotic

ECG types

1  degree AV block

2 degree  AV block – Type 1 Wenke bach

Complete heart blcok

Mechanisms

The inferior aspect of the heart has rich innervation of vagal nerve terminals (While the  sympathetic adrenergic system is concentrated in the anterior surface) . The moment infero posterior MI occur it stimualtes the vagus and a prompt bradycardic response occur .Many times the classical hypotension /bradycardia reaction is simply a reflection of heightened vagal tone.

Consequence of vagal tone on SA nodal and AV nodal conduction

As expected, vagal stimulation can result in a spectrum of arrhythmias from the  simple bradycardia to complete SA block  to  AV block. Extreme bradycardia , may release the junctional pace maker and result in junctional rhythm with a rate of around 40-50. There can be a functional AV dissociation between SA node and AV node. Careful ECG analysis is required here ,  as it can mimic organic AV block.The simple way to differentiate between organic AV block from simple AV dissociation is to look at the p waves.In AV dissociation both atrial rate and ventricular rate are nearly equal or VR  is slightly more than AR .In CHB atrial rate  exceeds ventricular  rate.

SA and AV block occur due to various mechanisms in inferior  MI

  • High vagal tone
  • Ischemia of SA/AV node
  • Necrosis of AV node
  • Drug effects -Like morphine
  • Reperfusion bradycardia*

Ischemic AV nodal arrhythmias are  some times very difficult to differentiate from vagotonia especially if occur within 24h.

Irreversible AV nodal block due to necrosis is rare.But if occur , usually  associated with extensive inferior mI/RVMI/ .AV block  that  persist beyond 48-72hours should raise the suspicion of damage to AV node.( As vagal tone is very unlikely;y to last beyond 48h)

* Some time a an episode of sudden severe  bradycardia  can be manifestation of RCA reperfusion.Flushing of SA nodal or AV nodal branch of RCA might trigger this. This has a potential  to  bring the heart to asystole.The resultant extreme bradycardia often triggers VT/VF .The reported high incidence of primary VF in infero posterior MI is attributed to this sudden RCA perfusion.

Medical management for CHB

Brady arrhythmia’s due to high vagal tone are generally benign .No specific intervention is required.Atropine will be suffice in most situations.Some times isoprenaline may be required. Aminophyline , now Ivabradine may have a role. Atropine not only corrects the HR it raises the BP also as  it counters  both cardioinhibitory and  vasodepressive  limbs of vagal stimulus mediated by  acetyl choline .

Pacing for Bradycardias in inferior MI.

  • Generally not necessary for sinus bradycardia.
  • Few with CHB require it
  • Persistent hypotension and RVMI  needs it often.(Dual chamber temporary pacing preferred as AV synchrony is vital here.)

Weaning of temporary pacing in inferior MI.

This could be a tricky issue. It can be weaned off in less than a week.A practical way is to use temporary pacing  only in back up mode at a heart rate of few beats less than the patients rhythm.Pacing for long hours  at high rates may delay the resumption of patients own rhythm and may result in false diagnosis of irreversible CHB and a subsequent PPM

How many will require permanent pacing following infero posterior MI ?

Only a fraction of patients with CHB require long term pacing . There are some centres tend to overuse PPM in this situation. Wait and watch policy may be the best.A unnecessary lead  within a  infarcted ventricle  has a potential to create problems .There have been  occasions a stable RV MI has been destabilised due to RV pacing lead triggered recurrent VF.

Tachycardias in inferior MI

It is relatively uncommon.Atrial involvement is more common with infero posterior MI and hence a greater incidence of atrial fibrillation .

RV MI can induce ventricular tachycardia arising  from the RV myocardium

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Total coronary artery occlusion is a common finding in CAD  especially in chronic stable angina. Normal coronary blood flow is 5 % of cardiac output  that amounts to 250-300ml/mt.At an average  heart rate of  70/mt  , each  beat  injects  about 5cc blood into the coronary circulation.This is shared between two coronary arteries.  This means , only few CC (2-3cc) of blood enters  each coronary artery with each cardiac cycle .

When one of coronary artery is totally occluded what happens to the coronary

blood flow ?

A.Total coronary blood flow  can be be  maintained   normal  at rest  as it  forms  only about 5% of cardiac output  (or it is only  slightly reduced )

B. It is believed , the unobstructed coronary artery  could receive the blood meant for the contralateral coronary artery. This  possibly explains the increased coronary artery diameter in the non obstructed artery.

C. It’s nature’s wish ,  that the  contralateral  coronary artery  shall share  50% of  it’s  blood through  collaterals if available.

D.If collaterals are not formed it , the unobstructed coronary  artery  may be over perfused with double the amount  of blood flow.

E. Some times , the collaterals steal  much more than what  the  obstructed coronary artery  deserves and make the feeding coronary artery ischemic. This is many times observed in  total RCA occlusion with well formed  collaterals  from LAD/LCX.

F.The collateral flow  in CTO also depend on whether flow is directed from LAD system to RCA or from RCA -LAD system. The LAD is better placed to assist RCA than vice versa.This is for two reasons.1.LAD blood flow is higher than RCA so it can share it.2.The driving pressure is more  from LAD -RCA , as RCA can receive  blood flow even during diastole .

F.During exertion , the coronary hemodynamics become further complex.The collateral’s are traditionally thought to be less than adequate during times of exercise.But it is more of a perception than solid scientific data.This rule  may be applicable in only certain group of patients. We know CTO patients with very good exercise tolerance who have documented collateral’s.

G.Collaterals can be either  visible or invisible by CAG. The strength of collateral circulation is not in it’s visibility but it’s capacity to dilate and  respond to neuro humoral mediators at times of  demand.  Currently  , there is lot to be desired  regarding  our knowledge about  the physiology  of visible collaterals , no need to  mention about invisible collaterals !

Final message

The above statements  are based  on logics and observations .

Is it not a  irony  in cardiac literature ,  where  thousands of articles  are coming out every month  to tackle  totally occluded coronary artery(CTOs) ,  there is  very little data   regarding the coronary hemodynamics in chronic total occlusion .   How  does a patient with CTO can manage a active life with only one functioning  coronary artery ?

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In  thrombolysis  of  STEMI ,  there is a   less  published ,  but   interesting observation . It is  often noted , variation  in the efficacy of streptokinase according to the time it was administered.It was most effective in the evenings and least effective in the early morning hours. The mechanism  is thought to be  due to  ,  pineal gland driven   endocrine   spikes    ,  that result in  a  less pronounced  progoagulant activity in the evening hours.    There could be a therapeutic significance for this phenomenon.

The following paper was presented as an abstract in the cardiological society of India annual scientific sessions in New Delhi in 1999.

CIRCADIAN

Download full PPT presentation stemi thrombolysis ppt

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When  a doctor is confronted by serious  doubt  ,  what will be the outcome for the patient  ?

Can  doubting  be beneficial for a patient ?  . It seems so ,  according to  EBM which  stresses   about statistical outcome at every turn of events in a  patient who  is critically  ill .

Is  something ,  always  better than  nothing   ?   Our  limbic  system tends to think so .  It  may not be true. But  in  dire situations ,   many  things  (Proven , unproven)  need to  be tried  however doubtful it ‘s  efficacy  may be  .This is  akin to an  emergency in an  airplane. Even here there need to be a logic.

Then ,this question  arises . How do we make  sure ,  we have a  dire situation on hand  ?

This is the key issue ,  in  the  decision making  for the   critically ill patients .  It  needs  experience ,  only experience !  Though the principle of uncertainty  is the fundamental rule in medicine ,   EBM  aims to bring some degree of certainty in medical therapeutics.

ebm evidence pci coronary

Benefits of doubting in coronary care unit.

In  a  sinking patient  with cardiogenic  shock  , try  the maximum treatment . Even if , the patient is  in severe shock  , take him to the  cath lab ,  try  open the coronary artery . Give the benefit of doubt  to him even though the chances of reviving him is less than 10%.

Risk of doubting in Coronary care unit.

A.Elderly STEMI  with SHT,(Arriving late ,  with  an unknown time  window  after an MI ) To thrombolyse or not ?  . There is  no benefit of doubt here.  Do not thrombolyse. Here , apply  the benefit of doubt against thrombolysis .

B. Chest pain with  LBBB (Thought to be new onset LBBB ) don’t ever rush to thrombolyse.  Wait for the enzyme result . Don’t try to thrombolyse your doubt , instead  thrombolyse the  confirmed thrombus !

C. Patient with persistent ST elevation following thrombolysis ,in an  otherwise asymptomatic and stable patient. Don’t  pass on  ” your doubt ” of salvaging   at least  some myocardium  by rescue PCI .Rescue  should be done before death. You can not resuscitate  dead myocytes.

Final message

The concept of   giving  the  benefits of doubt  to the patient   is a widely prevalent practice  in medicine .This concept is alive  and popular , not because it has proved effective, but because of the primitive   human perception and cognition  , namely “Something is better than nothing ” !

Common sense and logic would suggest , whenever  there is  a benefit  for doubting there would be a  equal (  or  even  more ) unmeasured  hazards and risks . This  becomes  especially  true ,  when   a   physician makes  a therapeutic move  based on doubting than on conviction .

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