Posts Tagged ‘ischemic ventricualr tachycardia’

Acute MI and ventricular tachycardia are closely related entities.In fact ,  the earliest response to ischemia could be a VT .But what  is peculiar about this VT is,  it  almost always degenerates into VF  within a minute or so.(Unlike idiopathic VTs /RVOT/LVOT VTs)

This arrhythmia in  every sense  can be called as  “primary VT which is the cause for “primary VF”

It is strongly  believed VF cannot occur without  a  brief episode of VT preceding it .Logic would also suggest  the ischemic myocardium  can not suddenly  become chaotic  “with the first  beat  “. There is little documentation available to unprove this presumption.

In spite of  this intimate relationship between VT and STEMI ,  it is very rare for a STEMI patient   to enter  ER with a sustained stable  ventricular tachycardia .  While  many VTs are known for it is hemodyanmic stability and immunity against degeneration   into  VF  , it is extremely rare  for  VT to remain as VT  in acute STEMI.

*Note : NSVT can be common   in  hospitalised patient in the coronary care unit . In our experience a sustained  VT in STEMI  will enter the VF mode within 60 seconds .If not , it is a highly  unusual phenomenon .

“But surprise is the other name of medicine ”

Here is  case report, a patient walked into coronary care unit with sustained( relatively stable) VT with LBBB morphology .We thought  it was   a  non- ischemic VT  (cardiomyopathy  , RVOT etc) .As we were examining him,  he became  unstable  and  was shocked 50 J biphasic .To our surprise a classical STEMI was unmasked and he was immediately  thrombolysed.

* It is possible ,  the patient had  suffered a  old MI  which got infarcted again and the VT  was scar mediated .

But it is still uncommon  for  it  not to degenerate into VF  with fresh  STEMI

Final message

Nearly all episodes of  ventricular tachycardia , that occur in the early minutes/ hours of  STEMI would degenerate into VF.This includes  VTs  that  occur within the CCU . Most  of the times , the CCU physicians and staffs  revert this VT  promptly and deny the  ventricles  from performing the dance of death !

It is extremely rare for an acute ischemic VT associated with STEMI to walk in to the hospital,  which our patient did !

Further reading and unanswered questions

  • What determines a VT to degenerate into VF ?
  • Why macro-reentrant , scar dependent VTs  often  are well tolerated ? ( In spite of LV dysfunction !)

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Ischemic ventricular tachycardia is a  too well recognised clinical  entity  . But , ischemia triggered atrial arrhythmias are less often encountered .

Does that mean , atria are relatively protected from the effects of ischemia ?

Not really  . . .  It  is possible  it may not be  that rare ,  as we think .

And then ,  the semantics play  a major  role !

Atrial fibrillation  is the commonest supra ventricular  arrhythmia  in human ,  we also know CAD is the leading cause of the AF apart from HT & Cardiomyopathy . So technically , ischemic SVT  is  more common than Ischemic VT ,but we do not call it so !

If we analyse the triggers for AF it is more often hypoxia  (than ischemia )  . . .yes there is huge difference between the two .In the ventricles it is more often ischemia that  trigger a VT.

Atrium is very sensitive to systemic  oxygen saturations especially in elderly and COPD patients. This is the reason we get many of the complex atrial arrhythmias in hypoxic situations ( Ectopic atrial, Multi focal atrial , etc) .These arrhythmias are difficult to control unless oxygen saturation is corrected. While  many of AF episodes are transient and disappear after correction of hypoxia.

If the ventricle also  responds with fibrillation  at times of systemic  hypoxia ,  one can  imagine the disastrous consequence ! God is kind enough , systemic hypoxia per se  rarely trigger a VF ,  though  it can maintain a VT which was initiated by some other mechanism.

So what are the causes of  narrow qrs tachycardia in the coronary setting

Apart from AF ,  Ischemic SVT  can occur in the following situations

  • Atrial infarction -Focal AT -Atrial flutter /AF
  • Post Pericarditis
  • Refractory , ischemic JT (Junctional tacycardia ) in elderly , perioperative , hypoxic patients

*Atrial arrhythmias are very rare during unstable angina for some unknown reasons . Atrial scar induced ischemic focal AT is underdiagnosed.

** Never  diagnose AVNRT /AVRT in a patient   who has an ACS. It is likely you will be 99.9% wrong.

*** Preexcited AVRTS are very rare in elderly CAD patients even in those with a history of SVT  .This is because as the age advances the accessory pathways undergo degeneration either by ischemia or  the wear and tear  and get self ablated .

Many times the associated , HT and diabetes may contribute to the arrhythmia.

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