Definition of Ventricular Tachycardia
Ventricular tachycardia (VT) is defined as a cardiac arrhythmia consisting of ≥3 consecutive complexes originating from the ventricles at a rate >100 beats per minute (cycle length <600 ms). 1
Key Defining Characteristics
The formal definition from the 2017 AHA/ACC/HRS guidelines establishes clear parameters 1:
- Minimum of 3 consecutive ventricular beats
- Heart rate exceeding 100 bpm (some sources cite >120 bpm in clinical practice 2)
- Origin below the AV node in the ventricular myocardium or conduction system 2
- Wide QRS complexes on ECG (typically >120 ms)
Classification System
VT is further categorized based on duration and morphology 1:
By Duration:
- Sustained VT: Lasting >30 seconds OR requiring termination due to hemodynamic compromise in <30 seconds
- Nonsustained VT (NSVT): ≥3 beats but terminating spontaneously before 30 seconds
By Morphology:
- Monomorphic VT: Stable, single QRS morphology beat-to-beat
- Polymorphic VT: Changing or multiform QRS morphology beat-to-beat
- Bidirectional VT: Beat-to-beat alternation in QRS frontal plane axis (often seen with digitalis toxicity or catecholaminergic polymorphic VT)
Important Clinical Distinctions
The rate threshold is somewhat flexible in clinical practice. While the guideline definition uses >100 bpm 1, emergency medicine literature often cites >120 bpm 2, reflecting that slower rates may represent accelerated idioventricular rhythm rather than true VT. The 3-beat minimum distinguishes VT from isolated premature ventricular complexes (PVCs) 1.
Origin is critical: VT arises from ventricular tissue distal to the His bundle bifurcation 3, distinguishing it from supraventricular tachycardia with aberrant conduction—a key differential diagnosis in wide-complex tachycardia 4, 2.
Common Pitfall
Do not confuse VT with ventricular flutter (regular VA at ~300 bpm with sinusoidal appearance) or ventricular fibrillation (rapid irregular activity >300 bpm) 1. These represent distinct entities on the ventricular arrhythmia spectrum with different management implications.