Measurement of the ventriculoatrial interval from the coronary sinus during para‐Hisian pacing may fail to distinguish ventriculoatrial nodal conduction from conduction over a septal accessory pathway

BACKGROUND: Para-Hisian pacing (PHP) helps differentiate retrograde conduction over an accessory pathway (AP) from retrograde conduction over the atrioventricular (AV) node. This study examined a potential limitation of this technique, focusing on the measurement of the ventriculoatrial (V-A) interval from the coronary sinus (CS) during PHP. METHODS: Our subjects were 9 patients undergoing electrophysiological studies before successful catheter ablation of a posteroseptal AP. During PHP, retrograde conduction occurred over an AP when the pacing stimulus to atrium (S-A) interval recorded near the AP remained unchanged whether the His bundle (HB) was captured or not (pattern 1), or when a loss of HB capture was associated with an increase in the S-A interval and no change in the V-A interval near the AP (pattern 2). RESULTS: Patterns 1 and 2 were observed in 5 (56%) and 2 (22%) patients, respectively. However, in the remaining 2 patients (22%), loss of HB capture during PHP was associated with an increase in the S-A interval (as in pattern 2), whereas the V-A interval near the AP could not be measured because no ventricular electrogram was visible on the CS recording (pattern 3); therefore, the presence of AP could not be confirmed by PHP. In patterns 2 and 3, the atrial activation sequence remained unchanged whether the HB was captured or not. CONCLUSIONS: PHP may not be able to discriminate between a retrograde septal AP and AV nodal conduction in patients whose proximal CS recording shows no visible ventricular electrogram.