Procedure for lead implantation

The 3830 lead, C315 HIS sheath (Medtronic Inc, Minneapolis, MN) and John Jiang’s connecting cable (Supplemental Figure 1) were used to perform LBBP. During the procedure, ECGs and pacing parameters were recorded by the tip electrode of the lead. The radiographic reference image of the tricuspid valve radiography in the right anterior oblique 30° projection was routinely set as an anatomical marker. The initial site for LBBP is approximately at the 1–3 o'clock region of the tricuspid annulus (Figure 1).

A: X-ray image of the tricuspid valve on the right anterior oblique 30° projection. The circle area is region of the initial site. B: The initial site for left bundle branch pacing. TV = tricuspid valve.

In the right anterior oblique 30° view, the lead with sheath was advanced from the right side of the septum to the left side. John Jiang’s connecting cable was connected with the lead for pace mapping at low output (2 V / 0.5 ms). When the tip of the pacing lead was fixed at the septum, the paced QRS morphology usually demonstrated a “W” shape with a mid notch in lead V₁. With advancement of the helix into the interventricular septum, the mid notch shifted toward the end of the QRS wave in lead V₁. The impedance of the tip electrode of the LBBP lead was monitored discontinuously at high output (5 V / 0.5 ms). With the abrupt shortening between the stimulation signal and peak LV activation (S-peak LVAT) in lead V5, LBBP lead continued to be screwed slightly (Figure 2). The duration of the pacing S-peak LVAT in lead V₅ was measured with LBBP lead pacing. Continuous unipolar pacing at low output (2 V / 0.5 ms) was performed during the subsequent period of LBBP lead implantation. When the first abrupt shortening by adjacent paced beats with the low output (2 V / 0.5 ms) was longer than 10 ms, the operator stopped screwing the tip of the LBBP lead (Figure 3). At the same time, the output was rapidly reduced, and the intracardiac paced QRS morphology was recorded by the LBBP lead. The depth of the lead position inside the LV septum was estimated by radiography with contrast injection in the left anterior oblique 45° projection.

A: Schematic diagram of pacing at different outputs (5 V / 0.5 ms; 2 V / 0.5 ms). B: The duration of the stimulus-to-peak left ventricular activation time before and after shortening at different outputs (5 V / 0.5 ms; 2 V / 0.5 ms). LBB = left bundle branch; PHB = penetrating his bundle; RBB = right bundle branch.

A: Schematic diagram of continuous pacing at low output (2 V / 0.5 ms). B: Duration of the stimulus-to-peak left ventricular activation time before and after shortening at low output (2 V / 0.5 ms). Abbreviations as in Figure 2.