How is ventricular tachycardia identified on ECG?

• A. Rapid wide-complex tachycardia (QRS ≥ 120 ms) with no clear P waves; monomorphic or polymorphic.
• B. Narrow complex tachycardia with clear P waves.
• C. Regularly irregular rhythm with variable PR.
• D. Slow rate with prolonged QT.

Answer: (A)

Ventricular tachycardia is a rapid rhythm that starts in the ventricles, so the electrical impulse travels through the myocardium rather than the normal His-Purkinje system. This creates a wide QRS complex, typically 120 ms or longer, during the tachycardia. Because the ventricles are driving the rhythm independently, the P waves may be hidden or not clearly related to the QRS complexes, and the QRS morphology can be monomorphic (same shape each beat) or polymorphic (varying shape). This combination—fast rate with wide QRS and little or no consistent P-QRS relationship—is the hallmark that points to ventricular tachycardia.

In contrast, a narrow-complex tachycardia with clear P waves usually indicates a supraventricular mechanism (like sinus tachycardia or AV nodal reentrant tachycardia), where the ventricles are activated through the normal conduction system. An rhythm that is regularly irregular with variable PR suggests atrial fibrillation with variable conduction, not VT. A slow rhythm with a prolonged QT points away from VT and toward other conditions associated with long QT intervals.