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Posts Tagged ‘fasicular tachycardia’

Ventricular tachycardia is considered as one of the most  dangerous  cardiac arrhythmia .Rather , it is the label  VT  that spreads more  fear than the arrhythmia itself. It is a fact many patients with VT walk into hospital , still  VT will always be a sinister arrhythmia as long as it carries a risk of degenerating into ventricular fibrillation.

What determines hemodynamic stability in VT ?

  • Origin and location of VT
  • The ventricular rate
  • Presence or absence of AV dissociation
  • Impact on mitral inflow pattern
  • Associated left ventricular dysfunction or valvular heart disease.
  • VT in the setting of acute coronary syndrome.(Ischemic VT)
  • Inappropriate drug selection

Origin and location

VTs originating high up in the ventricle( High septal VT,Proximal VTs) have more organised ventricular contraction  and they are more stable.Distal VT  originating  in the myocardium away from the conducting system has chaotic myocyte to myocyte conduction.These are very unstable.

The term fascicular VT is nothing but VTs originating  in the His bundle and it’s branches( Can also be termed Septal VT ).These VTs are also stable and some of them respond well to calcium blockers indicating that they are very close to the AV junction and carry the properties of junctional tachycardia. QRS width gives  a rough estimate about the location of VT. Narrower the VT higher it’s origin.( But remember even in VT ,  qrs can further widen on it’s way downhill !)

LV dysfunction.

This is probably the most important determinant of the outcome in VT. Patients with severe LV dysfunction (EF <30%) fare badly .Hence the land mark concepts from MADIT 1& 2 demanded ICDs in these patients.The most common clinical setting is  dilated cardiomyopathy.SomE of them have bundle branch re entry(BBR).This particular  VT can be stable for many  hours.

Ventricular rate.

Usually VT has a rate between 120-200.Higher the rate of VT more the chances of instability .This rule is also not always true as fascicular VT can be well tolerated at high rates.So location of VT focus  and LV dysfunction usually over rides the impact  of ventricular rate.

Mitral inflow pattern

Proper left ventricular filling is the key to hemodynamic stability in VT. In proximal, septal,fascicular, LVOT VTs doppler studies  suggest (ACC /AHA Type C evidence : Personal observations in CCU during VT) near normal preservation of  bi modal filling of mitral valve inflow.In ischemic myocardial VT  the mitral inflow profile is critically affected . There is no distinctive forward filling was observed .In fact  at rapid rates a short pulsatile MR jets are noted instead.

Associated valvular diseases

It is obvious,  aortic  and mitral valve disorders can aggravate the hemodyanmic instability.

Final message

The clinical behavior of  ventricular tachycardia is widely variable and dependent on multiple factors.

Associated LV dysfunction and  structural heart disease ultimately determine the outcome.

 

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