Ventricular Tachycardia (VT) on the ECG
Ventricular tachycardia is a broad-complex tachycardia arising below the bundle of His, defined as three or more consecutive ventricular beats at a rate above 100 per minute, with a QRS duration of 120 milliseconds or more.
ECG criteria
| Feature | What you see in VT |
|---|---|
| Rate | Usually 100–250 bpm. Above 250 the term ventricular flutter is used. |
| Rhythm | Regular, or very nearly so. Marked irregularity suggests polymorphic VT or pre-excited AF. |
| P wave | Usually invisible. When seen, P waves march independently of the QRS — AV dissociation, which is diagnostic. |
| PR interval | Not applicable. |
| QRS | 120 ms or wider, and often over 160 ms. Uniform shape in monomorphic VT; continuously changing in polymorphic VT. |
| ST-T | Discordant — the ST and T deflect opposite to the main QRS vector. |
How to spot it
- Establish that the QRS is genuinely wide. Measure it in the lead where it looks widest; do not eyeball it in one lead.
- Look for AV dissociation — P waves at their own slower rate, marching through the QRS complexes at no fixed relationship. It is present in most VT and it settles the diagnosis.
- Hunt for capture and fusion beats: an occasional narrow beat, or a hybrid, where a sinus impulse gets through. Rare, but effectively diagnostic.
- Check concordance across the chest leads. If V1 to V6 are all positive or all negative, VT is very likely.
- Look at extreme axis, between −90° and ±180°. Combined with a wide QRS this strongly favours a ventricular origin.
- Weigh the clinical context. Structural heart disease or previous infarction makes VT far more likely than any supraventricular alternative.
What it gets confused with
| Looks like | How to tell them apart |
|---|---|
| SVT with aberrancy | Favoured by a typical RBBB or LBBB pattern, a previous identical morphology in sinus rhythm, and no AV dissociation. Still the less likely option. |
| Pre-excited atrial fibrillation | Irregular, very fast, and with varying QRS width. VT is regular and its complexes are uniform. |
| Paced rhythm | Pacing spikes precede each complex. Look closely — spikes can be small on digital recordings. |
| Hyperkalaemia | A wide, slow, sine-wave rhythm with peaked T waves and flattened P waves. A metabolic emergency, not an arrhythmic one. |
| Artefact | Look for underlying QRS complexes marching through the "tachycardia" at the patient's real rate, and a patient who is entirely well. |
Traps
- Haemodynamic stability does not exclude VT. A young patient with a good blood pressure can still be in ventricular tachycardia, and treating them as SVT with verapamil can be fatal.
- Most broad-complex tachycardias are VT. If the tracing is wide, fast and regular, the base rate alone means the safest working diagnosis is VT.
- The various morphology algorithms are helpful when positive and unreliable when negative. Absence of the classic features does not rule VT out.
- AV dissociation is present more often than it is spotted — go looking for it deliberately in a long rhythm strip, not in a single 2.5-second lead.
- Polymorphic VT with a long QT is torsades de pointes and needs magnesium, not the standard VT pathway. Check the QT on any earlier tracing.
Why it happens
Most sustained monomorphic VT is re-entry around a fixed anatomical obstacle, typically scar from a previous myocardial infarction. Because the impulse spreads through ventricular muscle rather than the fast His-Purkinje system, depolarisation takes much longer, which is what makes the QRS broad. The atria continue under sinus control, producing the dissociation.
Why it matters
Ventricular tachycardia can degenerate into ventricular fibrillation, and it is the arrhythmia behind a large share of sudden cardiac deaths. It is also the one where diagnostic hesitation causes the most harm, because the treatment for the wrong answer is actively dangerous. Recognising it quickly and committing to it is the single most valuable rhythm skill on this list.
Questions
How do I tell VT from SVT with aberrancy?
AV dissociation, capture beats and fusion beats all confirm VT. Concordance across the chest leads, an extreme axis and a QRS above 160 ms favour it strongly. But base rates matter most: the majority of broad-complex tachycardias are VT, especially with a history of structural heart disease.
Can a patient be conscious and stable in VT?
Yes, and frequently are. Stability reflects rate, ventricular function and how long the rhythm has run — it says nothing about the origin of the arrhythmia and must not be used to argue against VT.
What is the difference between monomorphic and polymorphic VT?
Monomorphic VT has QRS complexes of a single, constant shape and usually arises from re-entry around scar. Polymorphic VT has complexes that change shape continuously; when it occurs with a long QT interval it is called torsades de pointes and is treated differently.
What is AV dissociation and why does it prove VT?
It means the atria and ventricles are beating independently. On the tracing, P waves march at their own slower rate with no fixed relationship to the QRS complexes. It shows the ventricles are being driven from below rather than from the atria.
Reading about ventricular tachycardia is not the same as calling it on a tracing you have never seen.
Practise on real cases in ECG Pro