Procedure description
Once vascular access is obtained, a guidewire is advanced into the right atrium (RA) or right ventricle (RV). A short 10.5F sheath is advanced over the wire to retain access. The EIS catheter is prepared normally. With the dilator inserted, the EIS catheter shaft can then be shaped for LBBP. The distal end of the EIS catheter, when maximally deflected forms two 90° deflections. The distance between the first deflection to the second 90° deflection is approximately 40.5±6.0 mm. While this distance has proved adequate for reaching the His bundle, it is too short for crossing the tricuspid valve and reaching the RV septum. Reshaping the EIS catheter proximal to the second deflection would extend our reach beyond the tricuspid valve, and in close proximity to our intended septal target. The further addition of a septal curve would allow us to maintain a perpendicular catheter orientation to the RV septum (Figure 1). The distal 25 mm of the IS-1 pacing lead (Tendril STS Model 2088TC) is stiff and non-deflectable, the septal curve can only be effective proximal to this point. Any attempts at introducing the septal curve in the distal 25 mm of the catheter would inevitably result in straightening of the shaped septal curve when the lead is introduced. Shaping the septal curve should thus be performed only between the first and second deflection of the EIS catheter, as this point falls between 3 - 7 cm of the lead tip when the lead is fully inserted.
Using a 0.035-inch guidewire, the entire assembly comprising the reshaped dilator and EIS catheter is advanced into the RA. The introducer and guidewire are then removed, followed by the introduction of a 58cm IS-1 pacing lead, which is advanced to the tip of the sheath. At this point, the distal tip of the lead need not be exposed beyond the sheath as the EIS catheter allows for both mapping and pacing via the distal platinum iridium electrodes.
The EIS catheter is connected to Merlin pacing system analyzer (PSA), and an electrophysiology recording system via the supreme electrophysiology cable and the use of stacked wires. The lead can also be connected in a unipolar fashion using threshold cables and stacked wires. The His bundle location can be mapped by using the EIS catheter and an X-Ray reference image set. Care should be taken during manipulation of the catheter in the RA, and inadvertent coronary sinus cannulation avoided by paying close attention to electrographic signals from the EIS catheter as well as fluoroscopic images.
The initial site for LBBP is approximately 1 to 1.5 cm distal to the His bundle location, in the RV septum along the line between the His bundle site and the RV apex in the right anterior oblique (30°) view. Advancing the reshaped catheter and with slight un-deflection would allow us to reach this area. Gentle counterclockwise rotation, and with the aid of the reshaped septal curve, a perpendicular septal orientation can be obtained (Figure 2).
The exact orientation of the EIS catheter to the septum should be determined in the left anterior oblique (30°) view. A more perpendicular septal orientation can be achieved by further un-deflecting and retracting the catheter, while maintaining gentle counterclockwise torque of the catheter. Pacing using the EIS catheter is then performed before lead fixation, with the aim of demonstrating a “w” pattern with a notch at the nadir of the QRS in lead V1, and discordant QRS morphology in the inferior leads (R in II taller than III), and in leads aVR/aVL (negative in aVR, positive in aVL, Figure 3A). The lead is advanced slightly beyond the sheath, and the helix extended. Unipolar pacing can be performed at this stage, and the pacing impedance documented.
Penetration of the lead into the septum can be achieved by rotation of the lead body. Unique to the EIS catheter, there are two specific points of resistance for effective transmission of torque to the lead tip; (1) the resistance incurred at the hemostasis valve on the lead body, which can be overcome with the insertion of the bypass tool (Figure 4A). Gentle forward pressure on the lead is required once the bypass tool is inserted to maintain pressure of the lead tip against the septum, (2) the two 90° deflection points can create resistance as well, especially when the stylet is fully inserted. This can be overcome by retracting the stylet proximal to both deflections (~9 to 10 cm, Figure 4B). The IS-1 pacing lead, with support from the sheath, has enough stiffness to allow for forward pressure to be applied and effective septal penetration without the need of a fully inserted stylet for support.
Clockwise rotation of the lead can be applied 3-4 turns at a time. The helix will inadvertently be retracted when the lead body is rotated clockwise (which can be confirmed with fluoroscopy). This can be overcome by re-extending the helix using the clip-on tool. Failure to re-extend the helix at this stage would lead to inadvertent lead dislodgement (Figure 5). The maneuver of lead body rotation and helix re-extension is repeated until the desired depth is achieved, and left bundle capture can be confirmed using previously described pacing techniques6 (Figure 3).
If perforation of the LV occurs, the lead should be withdrawn and repositioned. Withdrawing the lead should be done with counterclockwise rotation of the lead body while the helix is still extended. Retracting the helix prior to withdrawing of the lead body from the septum would entrap the helix in an extended position. The helix should be retracted only when the lead is fully withdrawn into the sheath.
Once the lead is in position, the catheter can be removed. The lead with the stylet still retracted is advanced to allow for adequate slack, while un-deflecting and retracting the sheath. The slitter tool has a unique lead stabilization channel that cups the lead and engages the shaft of the sheath. The slitter tool with the cupped lead can then be advanced into the hemostasis valve before engaging the lead into the lead retention channel on the slitter tool. The rest of the lead can then be guided into the thumbpad groove and secured with your thumb. The shaft of the catheter is aligned to the slitter tool reference line, and the catheter slit with a smooth axial motion.