Eccentric activation

• 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:

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1. Start testing with incremental atrial pacing, with at cycle length below that of sinus rhythm, with progressive, gradual shortening (-10ms) of the cycle length.
2. Pacing at increased rates produces prolonged A-V conduction time over the A-V node, which allows preexcitation to be manifested.
3. 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.
4. At A-V – node Wenckebach point, the conduction will be solely over the accessory pathway with maximal preexcitation.
5. Also try to check these properties with programmed atrial stimulation.