An extremely irritable focus can override higher pacemaker sites to cause a sustained run of PVCs. This phenomenon is called ventricular tachycardia (VT) (see Figure 6.5). If the PVC is ectopic, VT is an arrhythmia. The succession of PVCs in VT results in a rate of 150–250 bpm. The R-R interval may have a slightly irregular appearance but is generally uniform. 

Ventricular tachycardia has wide QRS complexes (> 120 milliseconds), as well as a T wave deflection opposite to that of the R wave. If a P wave is present, it is not seen before the QRS complex. VT is a potentially lethal rhythm that often deteriorates into ventricular fibrillation. VT can occur with or without a pulse.

Related Video – ECG Rhythm Review – Ventricular Tachycardia

Related Video – ECG Rhythm Review – Polymorphic Ventricular Tachycardia (Torsades de Pointes)

Figure 6.5. Ventricular Tachycardia

Ventricular Tachycardia ECG

Characteristics of Ventricular Tachycardia (VT)

1. Rhythm is usually regular, although it may be slightly irregular
2. Rate is typically 150 bpm–250 bpm
   1. If the rhythm progresses to a ventricular flutter, a rate > 250 bpm is possible
   2. The rate may occasionally be < 150 bpm, in which case it is called a slow ventricular tachycardia
3. P waves are not preceded by other P waves; dissociated P waves may be seen
4. No measurable PR interval is present
5. QRS complexes are wide and unusual looking (≥ 120 milliseconds)
6. T waves deflect in the opposite direction from the R wave
7. A pulse may or may not be present