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VT is 3 or more consecutive ventricular beats (wide QRS > 120ms) with rate of 100-250 (usually > 120).
VT with a rate of 100-120 is called slow VT. Misdiagnosis in slow VT may be deadly!
VT with rates >250 is called ventricular flutter.
The classic teaching when dealing with a wide complex regular tachycardia is to consider it VT until proven otherwise. However, there are several different types of VT and VT mimics to be aware of:
VT Types:
Lasts > 30 seconds.
Lasts < 30 seconds.
Impulses are regular & look alike, suggesting origination from the same ectopic focus. Occurs in structural heart disease & scars from prior MI/CAD. Caused by re-entry or electrolytes abnormalities.
QRS complexes have varying electrical axis and morphology & may be irregular. Most common cause is myocardial ischemia & MI. 2nd most common cause is prolonged QTc intervals.
Unstable form of PVT associated with long QT interval.
Type of VT where the QRS alternates in axis and morphology from beat to beat!
Type of monomorphic VT caused by re-entry in the fascicles of the LBB (Purkinje fibers).
Type of monomorphic VT originating from the RV outflow tract.
Hereditary form of PVT induced by emotional or physical stress
May be difficult to distinguish. When in doubt, assume it's VT!
Misdiagnosis of VT can be deadly, know when to suspect a mimic!
KEY PEARL
KEY PEARL
VT should have a heart rate > 120. Consider AIVR, hyperkalemia, & Na+ channel blocker toxicities when HR < 120!
Which part of the heart is causing VT?
Which part of the heart is causing VT?
ECG can be used to locate the ectopic focus
Right ventricle = LBBB appearance (dominant S wave in V1)
Left ventricle = RBBB (dominant R wave in V1)
KEY PEARL
KEY PEARL
When dealing with a regular REALLY wide complex tachycardia (RRWCT), it is critical to pause and consider the following:
DDx for RRWCT (QRS > 200 ms, or > 1 big box)
Toxicological and metabolic disturbances like hyperkalemia and Na+ channel blocker toxicities can cause RRWCT’s that mimic Ventricular Tachycardia
Lidocaine, amiodarone, and procainamide all have Na+ channel blocking properties and can worsen toxicities
Consider empiric treatment with calcium and bicarb before antiarrhythmics which can kill these patients!
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