Which discriminant differentiates VT from SVT?

• A. Stability
• B. QRS morphology
• C. Onset
• D. Rate

Answer: (C)

Onset of the tachycardia is a practical clue to where it originates. Ventricular tachycardia often begins abruptly because the ventricle is suddenly driven by an ectopic focus or an immediate reentry circuit, so the rhythm appears in a snap without a slow ramp. Supraventricular tachycardias, by contrast, typically develop more gradually as the atrial circuit or AV nodal conduction accelerates, creating a slower transition into the fast rhythm. Because this initiation pattern tends to differ between ventricular and supraventricular sources, onset is the best discriminator among the options given. Of course, there are exceptions, but onset remains a useful cue while stability, rate, and QRS morphology can overlap between VT and SVT.