In this patient, the His bundle potential with HV interval was 62 ms in the first position – left panel. The QRS amplitude was 1.9 mV and atrial activity could be easily identified on the EGM. Then the lead was moved towards the right ventricle to the para-hisian location – middle panel. The atrial activity was no longer recognizable, the QRS amplitude increased to 2.8 mV, and the HV interval shortened to 42 ms. Pacing with an output between 1.0 V–3.5 V at 0.5 ms led to myocardial capture of the ventricles (cSp capture was present with outputs above 3.5 V at 0.5 ms). The pacing lead was fixed inside the septum with 3 rotations – right panel. The QRS amplitude further increased to 3.5 mV and cSp capture occurred starting as 1.25 V at 0.5 ms (myocardial capture was present between outputs of 0.75–1.25 V at 0.5 ms). Asterisks show the first position of the lead.
Figure 2: Panel A: The method used to distinguish between RV septal, anterior, and lateral wall positions in the LAO projection. Panel B: the method used to differentiate between RVIT and RVOT lead positions within mSp in the RAO projection.