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Posts Tagged ‘limitations of lv ef’

LV ejection fraction (EF) is the most commonly used  LV systolic functional index.Since , it is an  easily acquired parameter,  it’s popularity has zoomed among both learned and novice cardiology professionals .(Not withstanding the serious shortcomings!)

In one of the evening rounds  in my CCU , a young cardiology fellow told me about a  patient  with acute  anterior MI with ST elevation V1 to V5.

The patient  was lying supine with trunk up . HR was 110 . BP was  100 /70 There were few basal crackles .The patient was undergoing  lysis with streptokinase.

It was  suggested  to me by the  fellow  that  the patient is  going in for “Impending  cardiogenic shock since his EF is just 30%”

That prompted me to ask this question

How good is the EF  a measure  of size of MI during STEMI ?

EF during  STEMI  is highly variable parameter.The following are important con-founders in LV EF measurement during STEMI.

 

  • Acute ischemia induced LV dysfunction .(Ischemic stunning from  the watershed zone  significantly over estimate LV dysfunction)
  • Mitral regurgitation  if present will underestimate it
  • Effect of tachycardia and bradycardia can be significant
  • The posture of the patient and  measurement errors (A good Simpson score is rarely  possible in a sick patient )
  • Associated  hemo -dynamic drugs like NTG/Dopamine etc which alter  pre and after load   and changes the frank starling forces.

* Please recall  , LV EF is never included as a criteria to diagnose cardiogenic  shock, confirming the  flimsy  nature of this parameter during acute phase of STEMI !

Final message

The purpose of echocardiography during STEMI is to rapidly identify any mechanical complication , not to waste time in calculating EF.

EF is not a good indicator  to  quantify the extent of STEMI  or it’s prognosis. LVEF cannot be used  to risk stratify STEMI in the first  48 hours .One can expect  the true LV function  to prevail only  at discharge.

Ideally ,LV  function should be reevaluated by 2 weeks to get a fair idea of true myocardial function .By this time all  confounders will resolve.

Clinical implication

Since many of us are suffering from an academic obsession and blindly follow the scientific guidelines, a hurriedly diagnosed  “severe”  LV dysfunction post STEMI may land our  patients to  inappropriate intervention !

 

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The LV ejection fraction ,  is  the most revered medical parameter for both physicians and cardiologists.There are anesthetists and surgeons , who  do not  operate  a  cardiac patient  without knowing it.There are  physicians  who  do monthly assessment of EF in their patients  with dilated  cardiomyopathy.

Now ,every one is interested to know what is their EF ?  Thanks to the global  information highway .We witness ,   patients who are extremely delighted when their  EF increases from 45% to 48% . Similarly , they get depressed when it falls by 2% .

Why this hoopla around the LV EF ?

Every one knows EF is nothing but a LV contractile force at a particular  beat of the heart . It is possibly a crudest possible way to screen for   LV function.( Of course it can still be useful  in patients  with established myocardial disease to follow up  LV dysfunction)

The  most important caveat in  EF is it’s dependence on the loading conditions  of heart .It is   also  heavily influenced by the  heart rate.We now, even a severely dysfunctional LV can contract vigorously with inotropic stimulation  like dobutamine  or whenever local catecholamines.

Our obsession with EF is complete and it is not expected to get cured in the near future.

There are many hundreds of articles in cardiology literature  which  ridicules the EF as sole parameter for assessing LV function. Still ,  it is the number one parameter to asses LV function  in real world as well as in  vast number of land mark clinical  trials .  Are all those trial  results to be doomed ?

Even as  the  LV EF is   being labeled as  futile index  ,   we  also  realise we have not traveled  far from our great clinical   ancestors . Thousands of  years ago   the Chinese  yellow  emperor  of medicine  found  the cardiac contractility  by pulse volume  and predicted death accurately  ,  probably  better  than the live 3d echocardiography   derived EF   guided by LV volume rendering algorithm !

The purpose of this article is to tell the current generation physicians  there are some simple and probably  accurate  clinical tips  to rule out significant LV dysfunction.

One can confidentially tell  the LV  EF  would  be > 50%  in 99% of population if they have the following !

  • A brisk upstroke of carotid pulse.*
  • A well palpated tapping apical impulse**
  • A Loud  first heart sound(S1)
  • A  totally normal ECG (Even a normal QRS complex  is suffice !) ***
  • Normal CT ratio in Xray chest
  • A  comfortable brisk walk of  at 6 km/hour for 10 m .

* A brisk central arterial pulse is nothing but the reflection of LV DP/DT a sophisticated echo parameter assessed  with much hype ! A good thumb with an   alert brain can accurately tell a given patients dp/dt is within normal range.

** A loud S1 and tapping apical impulse indicate the velocity of closure of  anterior mitral leaflet.Which is in turn reflect the force of contraction of the antero lateral  papillary muscle of LV .So what you hear a loud s1 is nothing but the contractile function of the most important  part of LV namely the pap muscle of LV.

*** A normal ECG ,  generally tells us  all is  well with LV myocardium . Finally,  it makes  immense sense to correlate the functional capacity to EF. (90% correlation)

Final message

Mind you ,  all the above modalities come either  free of cost or a fraction of  echocardiography  . It is estimated up to 90% echocardiography scans to R/O LV dysfunction can be avoided . The global health care costs can be saved and be utilised for some better purpose like protecting our atmospheric shell  from the  hazardous   gases

Note of caution

While ,one can rule out signficant LV dysfunction by above mode  ,  it can miss  other forms of LV dysfunction like relaxation defect etc . (ofcourse the EF also misses it !) .Judicious use of functional  imaging modalities are adviced in those who require it.

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