Para-Hisian Pacing
The accurate diagnosis of supraventricular tachycardias (SVTs) is crucial for the successful catheter ablation. To differentiate these SVTs, several pacing maneuvers are useful in the invasive electrophysiological (EP) study.
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Para-Hisian Pacing Kenzo Hirao
Keywords
Supraventricular tachycardia • Para-Hisian pacing • Atrioventricular accessory pathway • Atrioventricular node
4.1
Introduction
The accurate diagnosis of supraventricular tachycardias (SVTs) is crucial for the successful catheter ablation. To differentiate these SVTs, several pacing maneuvers are useful in the invasive electrophysiological (EP) study. The para-Hisian (PH) pacing technique is employed to identify the route of retrograde electrical conduction from the ventricle to the atrium. It has been considered as one of the reliable tools to establish whether a paraseptal atrioventricular (AV) accessory pathway (AP) is present or absent. Proper interpretation of the PH pacing, however, requires a systemic approach and an understanding of the potential pitfalls.
4.2
Concept of Para-Hisian Pacing
There are three factors affecting the ventricular-atrial (V-A) conduction in patients with Wolff-Parkinson-White (WPW) syndrome, which include the pacing site in the ventricle, pacing cycle length, and pacing stimulus strength. As shown in Fig. 4.1, in a case with only retrograde conduction over the AV node, a high output pacing stimulus captures both the right ventricle (RV) and His bundle; hence, a low output pacing stimulus captures only the RV, which changes the stimulus-atrial (S-A) interval dramatically.
K. Hirao, M.D. Cardiovascular Medicine, Tokyo Medical and Dental University, Tokyo, Japan e-mail: [email protected]
On the other hand, in a WPW syndrome case, either a high output or low output pacing stimulus causes a short S-A interval because the activation propagates similarly to the ventricular end of the AP as in Fig. 4.1b.
4.3
Techniques for Para-Hisian Pacing
This maneuver is not possible in cases with an absence of retrograde conduction, and in whom an isoproterenol administration should be considered to enhance the retrograde conduction over a concealed AV accessory pathway or the AV node.
4.3.1 Pacing Technique For PH pacing, a deflectable quadripolar catheter is positioned at the anterobasal right ventricular septum 1–2 cm anterior and apical to the His bundle best recording site, where a tiny His bundle potential can be recorded from the distal bipolar electrodes. The pacing is performed at a cycle length just shorter than the native rhythm, and the pacing output is started from a high value (20–40 mA), which may produce a narrower QRS complex indicating that the high output pacing has captured both the His bundle and local RV myocardium, HB/RV capture. Once having successfully achieved producing a narrower QRS complex, the pacing strength is decreased gradually until the QRS complex becomes wider, which indicates that the pacing is capturing only the RV septum (=only RV capture).
© Springer Nature Singapore Pte Ltd. 2018 K. Hirao (ed.), Catheter Ablation, https://doi.org/10.1007/978-981-10-4463-2_4
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