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Posts Tagged ‘ventricular’

Every one knows VT  presents as a wide qrs tachycardia  .Few of us ,   know VT can be narrow or even a normal qrs complex . But .none of us know what is the exact reason , why the width of  qrs complex  in VT swings from narrow  to wide.

Factors determining qrs width in VT.

  • Origin of VT :Septal, freewall , apex etc
  • Epicardial exit points make it wider
  • Rate dependent Intraventricular conduction (VT with aberrancy a possibility ?)
  • Drugged VT(Cumulative dose of amiodarone widens the  VT  )
  • Associated LV dysfunction/Myopathy
  • Electrolytic milieu (K + etc )
  • Preexisting bundle branch blocks (Surprisingly common and still more a surprise some BBB  may convert  a VT from wide qrs to narrow qrs ) 

* Another unique , but common observation is  variation in qrs width between different leads.This again points to different exit points and tachycardia circuits traversing and looping around the epicardium to endocardium at different depths  from the chest wall leads.

The commonest explanation of VT being narrow is it’s origin near the septum and travel down the fairly physiological his purkinje tracts and resultant uniform depolarisation.While myocardial,free wall apical VT are bizarre and wide. We now know , many factors come into play in determining the  qrs width.In fact , we are only beginning to understand the complex conduction pattern of VT.

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Aberrant cardiac conduction can occur in any of the specialized cardiac conduction tissues. Rate dependent aberrancy is the most common cause of aberrant conduction.

Generally it is thought only supra ventricular impulses can undergo aberrant conduction. But it is not always true.

Many of the ventricular tachycardia which  have inherently wide QRS complex can further widen their QRS width when it conducts fast down stream.This is especially true  in many of the septal VTs and fascicular VT  which  are falsely diagnosed as myocardial VT. These proximal VTs which other wise would have been a narrow QRS VT are converted into wide QRS VT by functional aberration .

Message :

Don’t always think SVT only has a potential to undergo with aberrancy

The VTs also can  behave similarly.

 

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