Differential pacing thus helps to identify a retroradely conducting pathway – similar to parahisian pacing. Parahisian pacing depends on having a similar stimulus to A time when direct his bundle capture is lost – however this distinction is based on the observation of a difference in QRS morphology – which at times can be very challenging to see. In such situation, differential pacing is valuable to confirm the parahisian pacing findings.
Similar to parahisian pacing, this maneuver also can be falsely negative for left sided pathways unless the pacing catheter is on the left side.
Compared to parahisian pacing, however direct atrial capture is unusual unless the catheter placement is very annular.
In practice, this maneuver is most useful after ablation – as the ablation catheter is steerable to the base and apex for pacing. Even in overt WPW patients, after an apparently successful ablation (i.e. loss of pre-excitation – delta wave), the retrograde component can remain – which can lead to tachycardia. This is where this maneuver is very useful – again in complementary with parahisian pacing