Eccentric activation

Acknowledgement

Piotr Buchta

Head of EP

What will you learn?

how to identify the eccentric antegrade activation / presence of preexcitation
interpretation of the changing morphology of the QRS complex with incremental atrial pacing
how to find maximum preexcitation and AV-node and accessory pathway refractoriness

The presence of preexcitation suggests the presence of an antegrade conducted accessory pathway (AP).
Typical WPW syndrome is characterized by short P-R interval below 120ms, a delta wave (slurred upstroke of the QRS complex) and wide QRS complex (wider than 120ms).
Most of the accessory pathways conduct both antegradly and retrogradly.
The degree of preexcitation it is always a competition - depends on the conduction velocity through the accessory pathway, the conduction velocity through the AV-node and His-Purkinje system and the mutual distance of these two structures. The slowing down of A-V node conduction at a constant AP conduction velocity results in the greater degree of preexcitation.
Remember to always test the retrograde conduction properties of the patient.
How to do it:

Start testing with incremental atrial pacing, with at cycle length below that of sinus rhythm, with progressive, gradual shortening (-10ms) of the cycle length.
Pacing at increased rates produces prolonged A-V conduction time over the A-V node, which allows preexcitation to be manifested.
You will see a change in QRS morphology as a result of fusion of conduction through the A-V node and the AP. By IAP observe a shortening of PQ interval, AH interval increases whereas the A-V interval remains stable so the HV interval will be shortening.
At A-V – node Wenckebach point, the conduction will be solely over the accessory pathway with maximal preexcitation.
Also try to check these properties with programmed atrial stimulation.