Left Bundle Branch Area Pacing
When targeting the left bundle branch directly we typically utilize the deflectable C304-HIS catheter, though the C315 His catheter can also be used as well as the C304-L69. Several methods of achieving left bundle capture have been described, typically we utilize an anatomic approach and target a site approximately 2cm apical to the tricuspid annulus and slightly inferior to the level of the His. When targeting the left bundle branch the lead tip must be advanced into the interventricular septum, usually to the depth of the ring electrode[12]. In this instance the principles described above to avoid cardiac perforation must be modified as tissue penetration is desired. The delivery catheter must be forcefully opposed to the interventricular septum with a moderate amount of forward pressure. When the catheter tip is directed to the desired anatomic location as identified in the right anterior oblique (RAO) view, the lead should then be advanced into the interventricular septum in the left anterior oblique (LAO) view to allow for assessment of depth of tissue penetration. Clockwise rotation should be applied to the lead while applying very gentle forward pressure. Almost invariably more than 5 rotations will be needed to achieve sufficient tissue depth for left bundle capture. After initial placement unipolar signals can be examined for a left bundle potential (not always observed even at sites of excellent pacing) then pacing is performed from the lead tip and the QRS morphology is evaluated. Unipolar pacing impedance should be high (> 800 ohms) when the lead tip is within the septum. The depth of penetration can also be assessed by unipolar pacing the ring electrode to assess whether the ring is buried. If left bundle capture is not observed further clockwise rotation should be applied, in many instances >10-15 rotations will usually be necessary. In some cases, delivering 4-5 rapid clockwise turns will improve tissue penetration as compared to a slower cadence of rotation. There have been multiple descriptions of how to assess left bundle capture[8, 13]. If the unipolar pacing impedance ever begins to decrease after the lead advances into the septum the lead should not be advanced any further, as this may be a sign the fixation helix has reached the left ventricular endocardial surface. In some instances, it will be challenging to advance the lead into the septum due to lack of support from the delivery catheter. In these cases we recommend ensuring that the delivery catheter is truly abutting the tissue; after initial lead fixation and while applying gentle backward traction on the lead the catheter can be advanced for more support. If it remains ambiguous whether the catheter is against the septum, contrast injection through the catheter side port can be instructive, in our experience this is rarely necessary. Finally, if multiple attempts have failed to achieve left bundle capture our experience suggests that attempting placement at a slightly more apical and inferior position will often be successful, likely due to the larger and more arborized left posterior fascicle (Figures 4,5).