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Posts Tagged ‘ventricular fibrillation’

ERS -Early repolarisation syndrome  is known as a   benign ECG finding  for  many decades  .Now it  is beginning to look dangerous as evidence is accumulating  it may have a link with ventricular arrhythmias.

ERS represents complex changes in  ionic movements during  cardiac repolarisation . (To be specific , it is due to a functional gain of  K + ionic channels during phase 3 of action potential).Generally this is a very benign condition. But , what concern us is ,  it can predispose to ventricular arrhythmias when these patients are confronted with ischemia .

When repolarisation occur early it indirectly shorts the QT interval .We know QT interval is a notorious period in human ECG as both a short and long (<320ms, > 460ms)  can be dangerous.

Is ERS a marker for potential cause for primary VF ?

Read this article from NEJM 2009

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Primary ventricular fibrillation is the number one killer in STEMI.It is  believed to occur  ( Rather it occurs really !) in up to 25 % of all patients with STEMI before they reach the hospital and another 4% after reaching the hospital.

What triggers this primary VF  ?

Easily answered : It is the  acute ischemia in majority.

Why it triggers in only in some patients? The  rest reach the ER safely and  some  casually walk in to the  OPD  few days  after a STEMI

This can never be answered with our current knowledge base. Some call this as fate !

Scientists should work hard on this issue, if we know the answer we could  possibly prevent the number one killer of the mankind at bay.

ventricular fibrillation ecg

Many factors are being analysed  to find the reasons for primary VF

  • Extent of infarct
  • Area of infarct
  • Intensity of pain
  • Adrenergic drive
  • Gender
  • Myocardial critical mass
  • Is it the  left main STEMI ?
  • Is it a bifurcation STEMI ?

If nothing  explains the VF it is always safe to blame it on susceptibility and inherited risk for primary VF , which of course is very much likely as the K+ channel  activity and it’s response to ischemia  is largely inherited

Is there any hot spots in the heart that are hypersensitive to ischemia ?

Some studies have clearly documented increased incidence of primary VF in infero posterior MI , and RV MI

than anterior MI .   J Am Coll Cardiol 2001; 37: 37-43

Why  ischemia of a certain location of heart should be more prone for  primary VF ?

The answer is any body’s guess.

Some intriguing possibilities are ,

  • RV is a anterior chamber , when infero posterior MI occur in association with RV MI  the ischemic zone encircles a almost 50% of heart like a band .This could be one explanation for more incidence of VF in infero postero RVMI.
  • Any MI which involves a  antero -posterior axis  of heart is likely to trigger a VF
  • Some of our patients  who survived a primary VF had a short left main  and early bifurcation with a large diagonal branch.The lesion was noted in the bifurcation.This raises a possibility ,  if a STEMI occur at a bifurcation with two divergent areas of  acute ischemia it has a high chance for precipitating a VF.

Related video by the author

Ignorance based cardiology -You tube

Potential research areas

Genetic susceptibility

Environmental Energy flows and primary VF

Some believe  a role for astrological  forces and  VF

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Acute coronary syndrome is the commonest cardiac emergency. STEMI and NSTEMI are the two clinical limbs of ACS. Generally they have distinct clinical, ECG, angiographic features.(Ofcourse,  with some degree of overlap) . It is  a  mystery , both clinical presentations differ so much inspite of the common denominator  , namely ,  an injured plaque with add on thrombus  within the coronary artery.

The mystery is since  decoded , the primary difference between these two entities is STEMI the occlusion occurs sudden and complete and in NSTEMI it occurs slow and incomplete

In STEMI ,  most of the clinical features and , need for emergent treatment , response to thrombolysis /PCI are dictated by the time dependent risk to myocardial loss .

Cardiac arrhythmias in ACS

It is a  much published  factoid   for  many decades  only one third of STEMI patients  reach the hospital alive ! The reason being , STEMI  is very much prone for primary VF.

Contrary  to this ,  almost all patients with NSTEMI reach the hospital alive ! How ?

Both are ACS, if ischemia is a powerful trigger for dangerous ventricular  arrhythmia’s ,  NSTEMI should also behave  similarly .

So what protects against arrhythmias in NSTEMI ?

  • We realise ,  by observational experience (Not EBM !)  It is the suddenness and totality of ischemia that trigger dangerous form of arrhythmia  .
  • Further, a balanced  ischemia in two contralateral segments (or global  ischemia) some how protects against development of ventricular  fibrillation .This may be due to preservation  of  electrical homogeneity  , and the spherical VT spiral waves are not sustainable.
  • In contrast , STEMI has a sudden  focal , ischemic  zone that initiates the VT and    ischemia free  contralateral segment  welcoming  and sustaining the  reentrant wavelet.
  • The observation of primarily single vessel disese in STEMI and multivessel disease in NSTEMI also give credence to this concept.
  • Further , ischemic preconditioning can exert an important anti arrhythmic  effect in NSTEMI as  patients with unstable angina have   slow, repetitive episodes of ischemia prior to the index event .
  • Post MI scar mediated VT/VF is independent of degree of overall ischemia
  • It is also established ,  a sub group of  STEMI pateints  who  had  preinfarction angina(  ie . a brief  period of UA/NSTEMI) have very low risk of SCD  supporting the concept of sensitising the myocardium against ventricular arrhythmias.

Final message

Even though , there is a convincing concept  of   ischemia induced  cardiac arrhythmia in literature , in real patients it is very difficult to link the two.

UA/NSTEMI is the most common  acute ischemic event but the incidence of VT/VF here,  is far less than one would expect.

In ACS , focal , total  ischemia is more likely to precipitate a VT/VF than multifocal and global ischemia.

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Ventricular fibrillation is invariably fatal if not treated . When can atrial fibrillation be fatal ? 

                                     Atrial fibrillation is relatively a benign arrhythmia especially when it occurs in isolation with  structurally normal heart.This is sometimes referred to lone atrial fibrillation . Even otherwise, atrial fibrillation is rarely fatal except in few situations.But AF commonly destabilises the patient  who have baseline valvular or myocardial disease.(Post MI, dilated cardiomyopathy etc)

There are few situations where AF can be life threatening

  • In patients  with WPW syndrome*where , AF  enters into a electrical short  circuit , downhill to enter the ventricle and make it fire at the same rate as that of atria . ( ie 400-600) and result in ventricular  fibrillation.Note , even here it is the VF that kills  not , AF per se.
  • AF in acute MI  often precipitates LVF , but rarely fatal.
  • In patients with critical aortic stenosis, or hypertrophic cardiomyopathy, sudden onset of AF can result in acute cardiac failure.
  • AF is often a terminal event in primary pulmonary hypertension

While atrial fibrillation is  less likely to cause  death , it is  a highly morbid arrhythmia .It is one of important cause of stroke in elderly as well as young !

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