Electrophysiologic Mechanism

During VT, the ventricles are being activated by an ectopic ventricular focus. If a sinus or atrial impulse happens to reach the AV node at a moment when:

1. the AV node is not refractory, and
2. the His–Purkinje system is not refractory,

…the supraventricular impulse can transiently override the ventricular focus and depolarize the ventricles normally.
This produces a single, narrow, normal‑looking QRS within a sequence of wide VT complexes.

A capture beat is therefore proof of AV nodal–His–Purkinje participation, and by extension, proof that the underlying rhythm is ventricular, not supraventricular.

ECG Appearance

A single narrow QRS complex within a run of wide, monomorphic VT

The captured beat resembles the patient’s baseline QRS

Timing corresponds to a sinus P wave (if visible)

Often accompanied by fusion beats in the same rhythm strip

Common Misinterpretations

• Mistaken for a PVC “resetting” the rhythm
• Misread as a supraventricular beat with aberrancy
• Overlooked entirely when P waves are not visible
• Clinical Implications
  Strongly supports the diagnosis of ventricular tachycardia
• Helps differentiate VT from SVT with aberrancy
• No treatment is directed at the capture beat itself; management targets the VT

Clinical Implications

Strongly supports the diagnosis of ventricular tachycardia

Helps differentiate VT from SVT with aberrancy

No treatment is directed at the capture beat itself; management targets the VT

Related Terms

Fusion beat

Ventricular tachycardia

AV dissociation

Supraventricular capture