ECG Basics · Lesson 15 · Putting it together
Wide-complex tachycardia and VT
QRS width helps organise a fast rhythm, but does not prove where it started. Read the rhythm and the clinical context together.
Wide is a description
An adult QRS of 120 ms or more is wide in the AHA tachyarrhythmia algorithm. Causes of a wide fast rhythm include ventricular tachycardia, a supraventricular rhythm with bundle branch block, pre-excitation and metabolic or drug effects. A monitor strip alone may not separate them.
What to describe
- Regularity: are RR intervals repeating or changing?
- Morphology: does the QRS shape stay similar (monomorphic), or change from beat to beat (polymorphic)?
- Atrial relationship: is there atrial activity independent of the QRS? AV dissociation can support VT, but its absence does not exclude it.
Compare the VT example with PSVT plus a bundle branch block layer. Both can look wide and regular. This model does not reproduce every clinical discriminator, including fusion and capture beats; its preset name is not a diagnostic test.
The ECG cannot establish perfusion
VT can occur with or without a pulse. The waveform does not supply blood pressure, consciousness or a pulse examination. This lesson teaches pattern observation; real emergencies require patient assessment and local resuscitation protocols.
References
- American Heart Association. Adult tachyarrhythmia with a pulse algorithm, 2025. QRS-width boundary and clinical assessment.
- American Heart Association. Adult Advanced Life Support, 2025. Wide-complex tachycardia, pacing capture and ECG artifact.
SIMULATED · NOT FOR DIAGNOSIS · TracingsMD ECG Basics