Mapping the unseen: Programmed electrical stimulation to detect concealed conduction block

Conduction blocks (CBs) play an important role in the initiation and perpetuation of atrial fibrillation and may be masked because of its direction- or rate dependency.

We aim to investigate how the highest amount and most severe CB at the right atrium (RA) can be unmasked by delivering programmed electrical stimulation (PES) from various directions and at different frequencies.

High-resolution epicardial mapping was performed at the middle of the RA on 40 patients during sinus rhythm (SR) and PES from the 4 sides of the mapping array at the average SR cycle length minus 50 ms (SR₅₀) and 3 different S1S2 trains (S1₄₀₀, S2₃₀₀, S2₂₅₀ or S2₂₀₀). CB area percentage (CBA%) was defined as the proportion of electrodes with a local conduction time ≥12 ms. CB severity was defined as the 95th percentile of the conduction times over the lines of CB.

CBA% increased from 0.6 [0-7.0]% during SR to 15.4 [12.3-19.2]% during S2₂₀₀ (P < .001). CB severity increased from 18 [14-29] ms during SR to 46 [29-53] ms during S2₂₀₀ (P < .001). PES increased CBA% over SR from 58% of patients during SR₅₀ to 100% during S2₂₀₀. The largest increase in CBA% occurred during S2₂₅₀ during pacing from perpendicular (+7.3 [0.5-10.8]%) and opposite (+7.4 [3.5-15.5]%) to the direction of SR.

Perpendicular pacing opposite to the direction of SR using premature stimuli is optimal for unmasking CB. PES may also reduce CB in patients who already exhibit complex activation patterns during SR.