Hurrah! Its time for pacing maneuvers

• how to recognise AVNRT right from the beginning
• what are the most effective and easiest pacing maneuvers
• practical tips how to make the diagnosis

AVNRT diagnosis is very likely when typical induction with AH jump is observed. However, you need to conduct additional pacing maneuvers. These maneuvers help confirm the diagnosis and differentiate it from EAT and AVRT:

1. VA interval: The typical VA interval in AVNRT is shorter than 70 ms on catheter that are close to AN Node like proximal CS or His catheter and shorter than 100ms on distal catheters like HRA or distal CS. This finding reflects rapid retrograde conduction through the AV node. It is measured from the onset of the ventricular electrogram (V) to the onset of the atrial electrogram (A) on intracardiac recordings. A good practice is to measure it from onset QRS to A on His, proximal CS or HRA catheter depending on operators’ preferences and clarity of the signal. Short VA intervals help distinguish AVNRT from other tachycardias, such as AVRT (VA more than 70 ms) or atrial tachycardia (variable VA interval).
2. Ventricular entertainment: during ventricular pacing with CL 10-30ms shorter than tachycardia, an atrial activation sequence remains unchanged (concealed fusion) because retrograde conduction occurs exclusively through the AV node (no accessory pathway involvement). It is essential to be sure that ventricular impulse is accelerating tachycardia and the CL of tachycardia equals CL of pacing. In this case atrial activation follows the ventricular pacing confirming retrograde conduction through the AV node (so called VA Linking).
3. Post-Pacing Interval (PPI) after ventricular entertainment: the difference between the PPI and the TCL is typically longer than 115 ms, indicating that the pacing side in RVA is far from the tachycardia circuit. It is important differential diagnostic criteria in comparison to AVRT as in AVRT ventricle (i.e. RVA) is a part of reentry.
4. VAV vs VAAV response to ventricular entertainment: the return sequence shows ventricular activation from RVA pacing (V) followed by atrial activation of a returning impulse conducted via fast pathway (A) and then another ventricular activation (V) as the previous A conducts downwards via slow pathway. This is a typical sequence for AVNRT as the reentry can be traced from RVA to A and then back to RVA. In contrast, EAT will give VAAV sequence that can be divided in VA and AV sequence. VA begins with V caused by RVA pacing which induce A via AV node conduction. This A resets the EAT which can lead either to termination or to next A that cause V through AV node conduction.