How do you differentiate AVNRT from AVRT on ECG?

• A. AVNRT typically has no delta waves and a very regular tachycardia with 1:1 AV conduction; AVRT uses an accessory pathway and may show pre-excitation (delta waves) or retrograde conduction
• B. AVNRT shows delta waves; AVRT never shows delta waves
• C. AVNRT has wide QRS complexes; AVRT has narrow QRS
• D. AVNRT is always irregular; AVRT is always regular

Answer: (A)

Differentiating AVNRT from AVRT on ECG hinges on pre-excitation and the pathway involved in conduction. AVNRT is a reentrant circuit inside or near the AV node, producing a very regular, narrow-complex tachycardia with a consistent 1:1 AV relationship and no pre-excitation. The atrial activity is often hidden in or immediately after the QRS, and you won’t see delta waves during sinus rhythm.

AVRT uses an accessory pathway between atrium and ventricle. If this pathway conducts antegradely, you get pre-excitation, which shows up as delta waves on sinus rhythm and a shortened PR interval. During tachycardia, conduction can be orthodromic (usually narrow QRS) or antidromic (often wide QRS), and retrograde atrial activation via the accessory pathway is common.

So the best distinction is that AVNRT lacks delta waves and features a very regular tachycardia with clear AV coupling, while AVRT involves an accessory pathway and may display pre-excitation (delta waves) or retrograde conduction.