Diagnostic significance of the morphological change in the atrial electrogram during Para-Hisian pacing

Para-Hisian Pacing: New Insights of an Old Pacing Maneuver

More than 2 decades ago, para-Hisian pacing was introduced to assess the pattern of retrograde conduction during electrophysiological studies. Although there is no ideal maneuver for every patient and condition, para-Hisian pacing is a valuable and handy strategy to differentiate between retrograde conduction over the atrioventricular node and the accessory pathways. The dynamic behavior of para-Hisian pacing, in a region with unique anatomical features, can produce various activation patterns and intriguing electrophysiological phenomena. Although the demonstration of a retrograde nodal activation pattern during para-Hisian pacing does not rule out the presence of an accessory pathway, evidence of retrograde conduction over an accessory pathway does not prove its active role in the culprit tachycardia. Multipolar His bundle recordings, detailed atrial mapping, and recognition of the truly captured structures and the impact of temporal changes of autonomic tone or pacing rates, are essential keys for accurate interpretation of this maneuver that may ultimately guide judicious catheter ablation of the arrhythmic substrate. This review aims to summarize the practical usefulness and potential pitfalls of the para-Hisian pacing maneuver, focusing on the interpretation of electrocardiograms and intracardiac recordings.

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.