Concentric depolarisation sequence

• basics of retrograde concentric activation
• how it looks like on the EP recording system
• how to check it quickly by pacing

• Retrograde conduction generally refers to atrial activation during tachycardia or ventricular pacing.
• In a significant proportion of patients undergoing EP testing, VA conduction over the AV node can be demonstrated either at baseline or using isoproterenol.
• The earliest part of the atrium to be depolarised is adjacent to the AV node, so the earliest atrial activation is registered by the His bundle catheter. Activation spreads out over both atria, with the coronary sinus atrial electrograms appearing in a clear proximal to distal sequence. This is termed concentric atrial activation.
• During ventricular extrastimulus testing, with increasingly premature ventricular extrastimuli, the VA interval will prolong. Eventually, retrograde conduction is blocked, when the His-Purkinje system or AV node becomes refractory.
• Main concentric activation with

-      earliest activation at the AV-junction (AVJ): AV node (fast pathway), septal accessory pathway (AP)

-      earliest activation at the CS ostium: AV node (slow pathway), septal AP

Tips and tricks:

Ventricular ES testing:

-      if ,A’ follows His, with same or longer HA interval -» AV-nodal conduction („His dependence”)

-      if ,A’ follows His, with shorter HA interval -» accessory pathway conduction („His independence)

Retrograde conduction may not be 1:1 during incremental ventricular pacing:

-      Gradual increase in VA interval with more rapid pacing, then VA Wenkebach point: indicative for AVN conduction

-      No or minimal increase in VA interval with more rapid pacing, then 2:1 VA block: indicative for AP conduction

Retrograde conduction in response to extrastimuli:

-      Gradual increase in HA interval after extrastimuli: indicative for AVN conduction

-      No or minimal increase in VA interval: indicative for AP conduction