Which rhythm has a circuit that goes from the atrium through the AV node to the ventricles and returns to the atrium via an accessory pathway?

Which rhythm has a circuit that goes from the atrium through the AV node to the ventricles and returns to the atrium via an accessory pathway?

• A. Orthodromic AVRT
• B. Antidromic AVRT
• C. Atrial tachycardia
• D. Atrial fibrillation

Answer: (A)

A reentrant tachycardia that uses two pathways, with antegrade conduction through the AV node and retrograde return to the atria via an accessory pathway, is orthodromic AVRT. In this rhythm, the impulse moves from the atria through the AV node to the ventricles, then travels back to the atria via the accessory pathway. The ventricles are activated through the normal His-Purkinje system, so the QRS is typically narrow, while atrial activation occurs retrogradely after the ventricular activation, which may produce P waves that are hidden in or follow the QRS. This pattern distinguishes it from antidromic AVRT (ventricles activated via the accessory pathway, producing a wide QRS) and from focal atrial tachycardia or atrial fibrillation, which do not rely on this AV node–accessory pathway reentrant circuit.

A reentrant tachycardia that uses two pathways, with antegrade conduction through the AV node and retrograde return to the atria via an accessory pathway, is orthodromic AVRT. In this rhythm, the impulse moves from the atria through the AV node to the ventricles, then travels back to the atria via the accessory pathway. The ventricles are activated through the normal His-Purkinje system, so the QRS is typically narrow, while atrial activation occurs retrogradely after the ventricular activation, which may produce P waves that are hidden in or follow the QRS. This pattern distinguishes it from antidromic AVRT (ventricles activated via the accessory pathway, producing a wide QRS) and from focal atrial tachycardia or atrial fibrillation, which do not rely on this AV node–accessory pathway reentrant circuit.