Theoretically, during low out put pacing, because of the time that it takes for the signal to reach the His bundle, the His deflection should be visible after pacing. During high output, the His signal should be buried in the pacing impulse as the stimulus directly enters his bundle
In other-words, a visible (measurable) stimulus to His deflection time would indicate loss of direct his bundle capture and now if the stimulus to A time remains same, there is a pathway.
However, for practical purposes, this is very difficult to demonstrate as the His signal usually is buried in the pacing impulse unless a high fidelity filtering system is in place.
The other factor to consider is fusion (AV node + pathway conduction)- this should be suspected if the retrograde atrial activation sequence is changed during the two phases of the test. However again most changes are subtle and requires careful playing with calipers on multiple electrodes pairs which show atrial signals (CS, HRA, His etc…)