What is a fusion beat in VT and what does it indicate?

• A. A QRS complex identical to VT morphology
• B. A QRS complex that captures sinus conduction completely
• C. A QRS that appears a blend of VT and normal conduction, indicating intermittent capture
• D. A QRS that is wider than VT

Answer: (C)

A fusion beat during ventricular tachycardia happens when two ventricular activation wavefronts occur in the same beat: the VT origin drives the ventricles, but a normal conduction impulse from the His-Purkinje system also reaches the ventricles at the same time. This produces a QRS that looks like a blend between the VT morphology and a normal, or near-normal, QRS. It indicates intermittent capture by the heart’s own conduction during VT—the ventricles are being activated partly by the VT and partly by normal conduction. In other words, the conduction system occasionally travels through during VT, creating this hybrid (fusion) appearance rather than a pure VT pattern or a fully normal beat.