Relationship between the most proximal His bundle and the morphology of intracavitary pressure curves

A precise localization of the most proximal His bundle (HB) is useful both for diagnostic and for therapeutic purposes, allowing the modification of atrioventricular (AV) nodal conduction. For selective diagnosis a bipolar lead is utilized; for therapy, a unipolar lead. The aim of the present study was to determine the relationship between the most proximal HB and the morphology of intracavitary pressure curves.In 15 patients (aged 64 ± 10 years), both bipolar and unipolar H-V intervals were continuously recorded while gradually withdrawing the catheter, which detected the pressure at its tip, from the right ventricle to the atrium. The longest bipolar H-V was 55.5±13 ms and the shortest 44.5±11 ms (P<0.001); the longest unipolar H-V was 56.5 ± 14 ms and the shortest 46.2±11 ms (P<0.001).During unipolar recording, H deflection was present in all patients at the same time as ventricular, transvalvular and atrial pressure curves; during bipolar recording, the H electrogram was not present in only one patient concomitantly with the atrial curve. During bipolar recording, the atrial H-V interval was greater than transvalvular H-V in nine patients (mean differences: 6 ± 2 ms) and they were equal in five; with unipolar recording the atrial H-V interval was greater than transvalvular H-V in 13 patients (mean difference: 8 ± 6 ms) and they were equal in two. In all patients, the H wave amplitude diminished from the transvalvular area to the atrial one.These data suggest that the values of the H-V interval recorded in the past have been underestimated. Furthermore, in order to modify AV nodal conduction selectively without damaging the HB it might be useful to record, in addition to the H deflection, the intracavitary pressure curves so as to deliver energy only when the tip of the catheter picks up an atrial curve.