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Archive for February, 2010

STEMI is the commonest cardiac emergency . Many believe , we  are close to  conquering  it .  It is hardly the truth .

  • The  mortality is  up to  30 % out of hospital and another 6-8  % within CCU  and another 2 %   at  30 days due to recurrent ACS   .This  is followed by an   annual attrition rate OF 25  due to progressive LV failure  .
  • The commonest mode of death is electrical,  ie primary VF.
  • Mechanical deaths are also equally important. Free wall rupture carries 100% mortality . Ischemic MR, Ventricular  septal rupture (VSR ) may also result in deaths.

Here is a case history and ECG of a  patient with STEMI .

After thrombolysis , the paradox happened . ST elevation  increased by 4mm and soon the patient became restless with worsening pain and became silent instantaneously ,  with monitor showing EMD and asystole .A diagnosis of free wall rupture was made.

What we used refer  in our CCU (Madras medical college Chennai .One of the oldest CCU in  South Asia )

as   “Action pontentialisation”  of surface ECG . This ECG finding has  great  clinical significance .

Here is a zoomed up view of a qrs complex of  the patient , which is very

closely resembles an action potential

Picture courtesey  http://ocw.tufts.edu/Content/50/lecturenotes/634488/634591

Pathological basis of  “Action potenial”  Like ECG

  • When the ST elevation is huge and wide it mimics  an action potential .
  • Myocyte action potentials are normally recorded epicardially in physiology lab where a  micro electrode with glass pipettes directly enter the myocyte.
  • A giant ST elevation and a sustained dome indicate , the quantum of  electrical injury is  very large and the  ECG electrodes is picking up the myocyte electrical events like that of a intra cellular electrode.
  • It is to be recognised  ,  ST elevation in chest leads is substantially taller than limb leads   because the exploring electrode  is located just above the myocardium . But,    when a  huge  ST elevation  is recorded  over a limb lead (as in this patient )  one can imagine ,   how intense the electrical  charge  of  the myocardium  should  have been  !

This heavy downpour of electrical energy that  emanate from the myocardium   means two things

  • The area of infarct is very substantial
  • The tissue in question is  very unstable .

Clinical correlates of  action potential ECG

  1. Damage is transmural , the   infarcted area is soft, friable and often hemorrhagic .
  2. The pericardium is also  likely to get involved in the injury process .
  3. The myocardium is  rupture prone or already torn .
  4. Even minor hemodynamic stress can be fatal in these patients
  5. An episode of vomiting, a fall in blood pressure,   an episode of  LVF or a short run of VT is suffice  to result in a fatality.

The death happens by a sudden rupture ,  EMD and asystole .

Can a life be saved  by the much fancied Emergency PCI  ?

Not really. The PCI  can not reverse the myocardial damage ,  so it’s role is little . But , any way it should be done and  .  .  . it  will  be done  in most institutions to give the benefit of doubt (Of course , with  a definite the risk of doubting  !)

What is the risk  of  PCI in these situation ?

The infarct related artery * if opened up can convert a bland infarct into a  “angry red”  hemorrhagic  infarct .This   is as good as  giving  the patient ,  a  farewell  party for his journey to heaven !

Note : Primary PCI  definitely  saves life in STMI . The  * is applicable only in persistent ST elevation , late after an acute MI.

How could  have the above death prevented ?

As one of the comments to this article  suggested, we need to have methods to identify impending rupture early and accurately .This should  followed by a prophylactic  surgical intervention (Reinforcing the friable myocardium – with a patch or mesh  )  .This is again not  a easy decision to make .

Final message

When the ECG  assumes  a shape of an  action potential ,  it is often a sign of  imminent  death  . Even though it may sound a pessimistic  view  it is often the truth  . Of course , an  emrgency PCI or  CABG  are  the only options available , we have  to be remember the above truth  ,   as we   play  those sophisticated  games  within their coronary arteries.

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The bundle of his divides into two

  • Anterior fascicle
  • Posterior fascicle
  • Middle septal  fascicle*

Middle fascicle * Many  dispute  it’s presence .  One may wonder , how  can anatomy be  under  dispute  ? If you cut a heart you should be able to clear the dispute .  But medicine is not that simple . . . What you do not see may be more important than what we see.

The anterior  fascicular block (LAFB) is one of the common conduction disorder. It ‘s significance :  Can  be a  benign  or a  dangerous entity depending upon the clinical situation .The  problem with  LAFB  is , it is diagnosed primarily by the axis shift it inflicts on the QRS complex.

In a strict sense, it is not a ideal way .There is  a tendency to label all significant left axis (> -60*) deviations  as LAFB. This  practice has made diagnosing LAFB very common in elderly, hypertensives, etc. In these situations it may not mean anything ,  except to suggest a  delay in conduction in  left anterior  fascicle.

If we filter out all these  benign  axis shift  ECGs  , the true organic pathological LAFB  may  not be that common .

Organic , LAFB occurs in the following situations.

  • Degenerative  blocks (Part of Lev & Lenegre’s disease)
  • Aortic valve disease .
  • Hypertensive heart disease
  • Post MI (Either alone or part of bifascicular or trifascicular block )
  • In association with dilated cardiomyopathy

Even in degenerative  , ischemic conduction defects LAFB is far more common than LPFB why ?

The traditional explanations are

  1. Anterior fascicle is relatively sub epicardial in location
  2. It is a  long and thin  structure prone to damage easily
  3. Exposed to the mechanical   stress of   LVOT **
  4. Anterior fascicle has  only a single blood supply(LAD)

** Which experiences  the peak LV  pressure  at > 100mhg and a dp/dt  up to  2000mmhg  (While,  the posterior fasicle is located  away  in the inflow portion of LV  , which is exposed  to low pressure – at best 10mmhg filling pressure )

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Human body is  now  approached by many of the physicians as  collection of  multiple  organs . This is  the price we pay for modernity in medical science. The era  of great physicians  in general medicine has gone . Now, a  super specialist  of one organ  is  rarely concerned about what is happening to the patient’s  other organ ,  it is  considered    foreign to him  ! While ,  this is the dominant thinking pattern of   modern-day specialist

Let us  travel intime  and  go to the year 1954 . . .

Three  physicians from Michigan ,USA  published  one of greatest observation in clinical sciences , namely the ECG changes in various forms of stroke .

Now , a shrewd physician  , will  suspect a subarachnoid hemorrhage (SAH) by looking at the ECG when the clinical situation demands . But , what we need is every one should develop that skill . We have seen errors happening  even in big institutions (or is it because it is big ?)  when  an elderly person comes with deep T  inversions with or without  altered sensorium being rushed into  CCUs  & cath labs instead of  neurology units.

We  need to teach  our junior  colleagues  . . .  That ,  ECGs of patients with  acute neurological syndromes  (ANS)  can mimic as acute coronary syndromes (ACS) ( especially in elderly ) .

The following ECG changes * are observed during stroke

  • Deep  T wave inversion –   Sub arachnoid hemorrhage
  • Cerebral thrombosis   –      Prolonged QT interval, U WAVES
  • Cerebral hemorrhage –      ST segment  shifts /T inversion

 

The ECG changes tend to occur very early after CNS injury.May last up to 1 week. They are not useful to identify the type of stroke. But , deep T wave inversions strongly suggest SAH rather than ICH or thrombotic stroke.

What is the mechanism of these ECG changes ? 

It is a clear proof that heart and brain are interconnected by neural network. All the noted changes occur during myocardial repolarisation . (ie ST segment )  The current thinking is  (Ofcourse , it is same as our thinking  in 1950s !)  it is mediated by adreneergic surge  initiated by CNS insult  transmitted to  myocardium by the sympathetic system.

Why should SAH produce more  ECG changes than others ?

It is possible the net adrenegic drive from the brainstem and spinal cord will be greater in SAH as it  spreads the entire CNS  through the cerbro spinal fluid. While localised ICH and infarct is  likely to generate less adrenergic impulse. 

Reference

Read the link to circulation 1964 .With courtesey to circualtionaha.com

http://circ.ahajournals.org/cgi/reprint/9/5/719.pdf

This came 50  years  ago , we still quote their work and no one has improved their work . 

Final message

If  only  we make the  clinical bed side teaching as a  regualr habit ,  we  do  justice to   our  great  physicians of the past ,   who enriched  our  life  with their  clinical  skills  and  passion for knowledge  sharing .

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As the name suggests   dilated cardiomyopathy  would imply  cardiac chambers will dilate , at least some time in the course of the disease .It can be minimal, mild or massive. A new entity called  non dilated cardiomyopathy is also gaining wider acceptance . (That will be dealt seperately )

Logic would suggest , the first chamber to dilate in DCM  should be the left ventricle because it is  facing the direct load of systemic blood. But we also know , whenever  LV is stressed , left atrium comes to it’s assistance .

Left atrium does this    by total self sacrifice ( by all  means!)  increases  it’s  force of contraction, elevating it’s  mean pressure or even increasing it’s rate (AF) .

Like most  other critical questions in cardiology  ,  the factors that determine LV dilatation in DCM ,  is  also poorly understood !

  1. Is it the after load ?
  2. Is it the  muscle mass ? or it’s turgid  or flabbiness ?
  3. Is it the interstitial integrity?
  4. Is it the blood volume ?(LVEDV ,  LV residual volume )

When the issue is complex , it is  usual  to  make the   the unknown  genetic defects  ,  the scapegoat !

As of now the most important determinant of LV dilatation  could be  the behavior of the desmins, the gap junctions and myosins the titins etc

If  the LV of a DCM patient  refuses  or  resists  dilatation what  might happen ? Is it good or bad for the patient ?

Here is a catch .  A  LV  that does not dilate  obviously should be  be good for the patient  is in’t ? Medicine is not that simple.

When   LV  fails to  dilate  it means it has become  too  stiff and rigid    and pass on the  burden to  to LA which  faces the music. And in the process it dilates.This is the reason , we  observe  diastolic dysfunction in vast number of DCM patients.( Currently it is estimated > 75% DCM will have significant diastolic dysfunction )

So , now we can imagine how complex the sequence of hemodynamic stress in DCM that determine the chamber enlargement.( RA, RV  dimension in DCM is a separate issue !)

So now answer this question :  Which chamber dilates first in DCM ?

  1. Left ventricle
  2. Left Atrium
  3. Any of the above
  4. Both of the above dilate simultaneously

The answer must be 3 .

Why  recognising this sequence of  chamber enlargement  in DCM   is important ?

  • It gives us an opportunity to assess the dominant mechanism of LV dysfunction.There are reports , where some  DCMs  have more diastolic dysfunction than systolic dysfunction  .This will have important therapeutic implication.Further , many of the infiltrative   disorders of LV can have features of both DCM & RCM .
  • When a RCM begins to dilate it is usually  a harbinger of terminal heart failure. But,  it need not be always true .  A small restrictive LV  , when  dilates ,   may acquire a  slightly improved diastolic properties , as the  LV becomes more placid . And ,  if it happens the LA size may regress.
  • The role of LV restriction devices like, Acron mesh, Dor procedure, plication  in refractory  DCM is not well defined. All these   modalities actually  adds  a small dose of diastolic dysfunction in these patients who have grossly dilated ventricles. This fact is  very important  , as presence of any preexisting  significant diastolic dysfunction in DCM makes  the role of LV restrictive devices and surgery a big question mark !

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Imaging  coroanry artery is  generally  in the   domain of interventional cardiologists. MDCT has helped us to change that.

The  humble echocardiography can   identify the origin* of   coronary arteries   in  most   persons. The resolution power of modern day echocardiography is  2mm and the left main  ostium is >3.5mm in 99%  of population . If some body says one can’t  visualise the coronary artery by echo ,   it can only reflect their ignorance or lack of patience to get an optimal image. Of course technological limitations are there.

*  To be emphasised again , only the origin can be identified.

Can we identify ostial leftmain or proximal  left main disease  by echocardiography ?

It should be possible in  few .

Can we place  a doppler sample volume  within  the left main and measure coronary flow velocity ?

When obsterticians are able to  assess the  uterine artery flow  in a bulky uterus ,  it should be possible to do the same in  a coronary artery . Motion artifacts is the issue in the heart.  Micro sample voulme (<1mm) are expected in the future  that will make a non invasive coronary flow assesment a distinct possibility.

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Hypotension is one of the dreaded complication of acute STEMI.

  • It can be due to either a  mechanical complication or hypovolemia.
  • The hypotension in inferoposterior MI is  often related to enhanced vagal tone and easily correctable with atropine  and fluid  administration.
  • RVMI is the classical example of hypotension that may improve with fluid resuscitation
  • Hypotension,  if  not reversible within 12  hours  ,  is more likely to  represent a more sinister mechanism like pump failure, MR or ventricular  septal tear etc .

A new mechanism for persistent  hypotension is increasingly recognised.

This is due to the

1.Loss of LVOT dynamic activity.

2.Excessive  dynamism of LVOT.

LVOT contractile and ejectile falure

Even though LV  outflow tract  contain  less  contractile myocytes  , it has an important mechanical  job to do. We know , it’s  primary job is that of a  conduit  but  it also  has to  eject the blood into aorta with sufficient force.  In fact, it is thought much of the acceleration of blood velocity occur in LVOT . So, LVOT  plays a key role in maintaining the cardiac index.  An excessively dynamic LVOT will impede the forward blood flow as in HCOM.  Similarly  less dynamic contraction  of LVOT  results in  low velocity propulsion , that interferes with   proper delivery of blood from LV cavity into the aorta .

These factors get amplified in  acute MI , as it is a compromised situation with fluctuating HR and contractility. So a properly functioning  LVOT conduit is  absolutely mandatory.

STEMI due to a proximal LAD obstruction   located can involve the septal .If the first septal branch  happens to be a major one,  there will be  definite impact on the LVOT function.

Excessive dynamism  , LVOT   desynchrony  LVOT collapse .

LVOT has a medial border formed  by IVS , an  anterior surface and  a posterior surface .The lateral border is relatively boundary less , except it is guarded by  the anterior mitral leaflet.

But one should recall , the AML comes towards the LVOT only in diastole . When it comes in systole it becomes a pathological event  called  SAM  (Systolic anterior motion )

The LVOT wall desynchrony can occur in both anterior and posterior MI.In a mulivessel CAD  this can happen when there is disproportionate inferior to anterior wall motion defect.

Management.

  • There is no specific management strategies aimed at restoring LVOT function.
  • Emergency revascularisation will attenuate the mechanical dysfunction
  • Dosage of powerful inotropic agents should be moderated in dynamic LVOT obstruction.
  • Spontaneous recovery  may occur in few

http://circ.ahajournals.org/cgi/reprint/116/5/e110.pdf

Haley et all Mayoclinciproceedings 1999

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  • It is only rarely a journal of International caliber is published from India . IJEP is one such journal.
  • Cutting edge articles on Electrophysiological science  break here !
  • This is an online journal . No print issues . Enjoy, it is free !

Here is the  Link

Just sample an article  : A great review about cardiac arrhythmias in congenital heart diseases , Must read by  all cardiologists    http://www.ipej.org/0906/khairy.htm

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  • It is going to be the era of non invasive imaging  in  cardiovascular  diseases .Future looks very exciting
  • We have now ability to slice the heart 356 times a second !
  • Image resolutions are getting sharper .
  • The only worry ( Of course a major one !)  would be the radiation , that has to be addressed .

Now we have a dedicated journal for cardiovascular CT scan .

Does it surprise you  ?   For me  . . . It  is  !

Link to the current journal page . Get updated  !

http://www.journalofcardiovascularct.com/current

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There are millions of  articles in cardiology . Some  simply  occupy   valuable spaces without any purpose  . Some give us knowledge . Some enlighten  us. While few are  so vital , it is almost a crime  if we do not read such articles and apply  it in day to day  practice .

This an article  written by Henri Justino that has a immense importance for the patients as well as the physicians .

Do not think  the article which came in pediatric radiology  is not applicable in adults !

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  • Here is a site which has dedicated  resources for learning echocardiography .
  • The site has collection of various work shop and conference highlights
  • The basic echocardiography with classical line diagrams  would be very much useful for the beginners,

Cheers to duke university for sharing ! www.echoincontext.com

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