Introduction
Right ventricular (RV) apical pacing causes ventricular dyssynchrony with an increased risk of heart failure [1]. Despite attempts to reduce it by changing the pacing location (RV septal vs. RV apex), no clinical benefit has been observed. As was shown, the standard fluoroscopic criteria for exact lead placement are insufficient, and many leads that were considered to be in the septum based on fluoroscopy, were, in fact, anchored in the anterior wall [2, 3]. Furthermore, septal positions might represent a mix of more or less dyssynchronous pacing, which ultimately brings no advantage over RV apical pacing.
In recent years, His bundle pacing (HBP) has shown promising results [4], but its benefits are counterbalanced by an increase in pacing lead reinterventions [5]. These shortcomings could potentially be moderated by placing the lead tip in the ventricular septal para-hisian area, beyond the annulus of the tricuspid valve. This would ensure pure myocardial capture during low output pacing and concomitant myocardial and conductive tissue capture during higher output pacing. In our study, we called the high-output para-hisian capture as conductive system septal pacing (cSp) to differentiate it from myocardial septal (mSp) or pure myocardial para-hisian pacing in which conduction tissue is not captured directly.
UHF-ECG is an imaging method displaying the activation pattern and time differences between the activation of specific ventricular segments. Time-spatial resolution is possible thanks to an analysis of the ultra-high frequency components of ventricular myocyte action potentials in peri-myocardial tissue and the practical use of UHF-ECG was documented in previous reports [6, 7].
The aim of the study was to describe in detail the activation patterns seen during RV pacing with and without direct conduction system engagement.