Clinical presentation of ventricular tachycardias : How outflow tract VTs are different form other VTs ?
Posted Feb 03 2009 12:09am
Ventricular tachycardia (VT) is one of the dangerous form of cardiac arrhythmias.When it occurs , it may present in many ways
Cardiac arrest with immediate degeneration into ventricular fibrillation.
Pulseless VT in a conscious patient but in in shock.
With pulse, realatively stable , not much fall in blood pressure.
This , gives us an idea that VT as an electrical abnormality has wide clincal presentations , life threatening at one end and pateint walking into the hospital with minimal palpitation !
The management issues
In patients with hemodynamic instability , decision making is easy as there is only option of DC shock.
In patients with stable VT, it is natural for the physicians to get tentative or even confused.This is because , dangers of shocking a stable patient has to be weighed against the currently available excellent antiarrhytmic drugs( Amiodarone, Ibutilide etc) .
The major issue here is in ruling out underlying structural heart disease.
Never shock a stable VT, without knowing the myocardial and valvular function.There has been many occasions underlying severe LV dysfunction is missed and they may go for asystole.
VT in the setting of cardiomyopathy, Post MI(Scar mediated) are often refractory even to DC shocks.It is the drugs that will ultimately control the arrhythmia.DC shock is just used to terminate the VT.
VT structurally normal heart , especially arising the outflow tracts of LV or RV behave very differently (Fortunately they are more benign)
Have less hemodynamic impact as it involves the outflow tract and not over the the pumping zone of LV as in conventional ischemic myocardial VT .
They respond to calcium blockers verapamil to be precise (As they share properties of SVTs)
Sensitivity to verapamil by no way convey a meaning of Amiodarone resistance.Out flow tract VTs will also respond to Amiodarone many times.
Degeneration into VF is rare.
Also read Therapeutic issues in stable ventricular tachycardia