Well, there is something called the Brugada criteria which is used to distinguish between regular monomorphic wide QRS complex tachycardias/SVT and ventricular tachycardia....Kind of boring, so here is what I learned from ACLS!
Wide QRS complexes include PVCs, monomorphic V tach, polymorphic V tach, torsades de pointes and V fib...SO you see why it is a good thing to know the significance of the PVCs that you are observing
Monomorphic V tach is the most common form of ventricular tachycardia. It is considered life-threatening, as you know, because it may lead to ventricular fibrillation. What causes it? Usually myocardial irritability and circuit reentry, usually precipitated by a PVC that occurred during the period of ventricular repolarization, a/k/a R-on-T .
Polymorphic v tach, well the complex itself is unstable, as it varies from the site of origin throughout the ventricle. By-the-by, Polymorphic Ventricular Tachycardia is associated with a much poorer prognosis than monomorphic
Torsades de pointes is also life-threatening; also a polymorphic ventricular tachycardia, and it CAN degenerate into ventricular fibrillation.
Treatment for all of the above: Amiodarone (for Torsades administer Magnesium) and if patient unstable, debfibrillation.
When you are talking about narrow complex tachycardia (QRS < 0.12 seconds) and wide complex tachycardias (QRS >/= 0.12 seconds) you've gotta identify the type of tachycardia and treat appropriately
If it is narrow complex and regular, attempt vagal maneuvers then adenosine. IF irregular narrow complex could it be a. fib or atrial flutter?? Use diltiazem (I would use that first instead of a beta adrenergic blocker especially if I don't know the patient's Hx like pulmonary disease...)
IF wide QRS and patient STABLE then assess if regular or irregular. If appears regular amiodarone and prepare for synchronized cardioversion. IF irregular would also suggest amiodarone and call for consult. If Torsades, Mag sulfate.
Hope this helps!