Left bundle branch area pacing (LBBAP) is increasingly being performed because of the relative ease of implantation and the positive outcomes when compared to conventional right ventricular pacing or even cardiac resynchronization therapy (CRT). In this lesson we aim to provide you with the most essential aspects of LBBAP implantation.

The first step of LBBAP is to access the heart and place a guiding catheter in the RV, perpendicular to the interventricular septum. The next step is to penetrate an active fixation pacing lead through the septum, until there is capture of the Purkinje fibers of the left bundle branch network.

Penetration of the interventricular septum is performed through lead body rotations, which is the essential difference between LBBAP and conventional RV lead placement.

LBBAP may be performed using either conventional leads which are stylet-driven or using a lumenless lead. While LBBAP was initially performed using lumenless leads as they are thinner and imperative for His bundle pacing, stylet-driven leads may offer more support for easier penetration of the septum.

On MicroportAcademy, we have two videos which explain both procedures:

LBBAP using lumenless lead (link to video lesson):

LBBAP using stylet-driven lead video (link to video lesson):

Ten things to know for successful LBBAP

While the video will guide you through the basics of LBBAP success, here are a few aspects which will surely improve your implantations.

1. R prime in V1

When pacing the tip of the lead (unipolar pacing), we aim to see a final positive component of the QRS wave in lead V1, which is called the R-wave prime (R’). This feature is a result of delayed RV activation (incomplete right bundle branch block) and a strong argument for capture of the left bundle branch area.

See below in the picture the R’ in lead V1 (green line):

It is important to note that the emergence of the R’ is not essential for LBBAP success. This could be due to placement of the precordial electrodes or due to more distal capture of the left bundle branch network. However, it has been shown that the R’ and even the relative size of the R’ is indicative of positive outcomes.

2. LVAT <80 ms in V5/V6

Left ventricular activation time (LVAT) is a measurement performed on either lead V6 or V5 by placing calipers on the pacing artefact and on the peak of the QRS complex. This gives us an idea of the activation of the left ventricle, which is expected to be much faster when recruiting the left bundle branch fibers.

Here is an example of a short LVAT (<80 ms), indicating capture of the left bundle branch:

The LVAT, like the R’, is an essential aspect of LBBAP. We should see shortening of the LVAT during penetration of the septum with also smoothening of the R-wave (no fractionation). When there is an RS wave in V5/V6, it may be better to use lead I or aVL instead.

3. Interpeak (V5/V6 – V1) of at least 33 milliseconds

In the figure above, we see a second measurement, this is the interpeak time. The interpeak time stands for the duration between the left ventricular activation (peak in V5/V6) and the activation of the right ventricle (R’). When the interpeak time is prolonged (>33 ms), it indicates that we have succeeded in uncoupling the LV from the RV, a strong argument of LBBAP. If the interpeak is even longer, more than 44 ms, there is 100% specificity of LBBAP.

4. Fixation beats

When you encounter premature ventricular beats during screwing, it is very interesting to look at the morphology of those complexes. If these complexes have incomplete right bundle branch morphology, it is very indicative of your lead tip being in proximity of the left bundle branch. Appearance of premature ventricular complexes with incomplete right bundle branch block is a sign to stop screwing and to perform lead measurements.

The figure below shows a small emerging R’ in lead 1 during screwing and then PVCs with incomplete right bundle branch morphology indicating proximity of the helix to the left bundle branch. (the figures above are taking directly after this screen).

5. LVAT change during 10 Volt pacing

When performing pacing tests after penetration of the septum, it is recommended to pace also at high output (for example 10 Volts). If the LVAT shortens during high-output pacing, it indicates that the tip of the lead is in vicinity of the left bundle branch and a few more screws may result in more selective LBBAP. Example of this phenomenon is shown in the videos (links above).

6. QRS ≤ 130 ms

Most experts agree that LBBAP should result in a narrow QRS with QRS duration of 130 ms or less. This is a common cut-off also used in most studies evaluating the effects of LBBAP.

7. Morphology change during threshold test

When performing pacing tests after penetration of the septum, and you see significant changes in QRS morphology (for example appearance of R’), it is a strong indication of LBBAP. The only way to explain the sudden difference in QRS morphology during threshold testing is that at first, you capture both the left bundle branch fibers and the surrounding myocytes (non-selective capture)), and then you lose capture of the ventricular myocytes but still have capture of the left bundle branch (selective capture). This is therefore a very strong argument for (selective) LBBAP.

8. EGM

When performing pacing tests after penetration of the septum, it is important to look at the EGM during sensing (ODO mode when possible). We aim to see a positive R-wave with injury current. An R/S or qS wave on the EGM without significant injury current may be a sign of crossing of the left ventricular endocardium and that the lead tip is actually in the left ventricle. This has to be avoided as it leads to capture problems, lead instability and risk of stroke.

9. Impedance

While there are no golden rules for impedance (changes) in LBBAP, we do always see a rising of pacing impedance during penetration of the septum. When the impedance starts to decline, it is a sign that the lead tip is close to the left ventricular endocardium. A drop in impedance is a sign to stop screwing the lead and perform measurements, ensuring that you did not cross the septum.

10. Fulcram sign

When lead tests are satisfactory, it is worthwhile to look how the lead is moving along the septum and in the RV using fluoroscopy. Typically, we see a fixed distal part of the lead within the septum, and a more mobile peart of the lead in the RV separated by a hinge point. This phenomenon is called the Fulcram sign and is also shown in the videos.

Note: these 10 rules are not set in stone and may be subject to operator opinions and evolving literature. If you have any questions or comments, please don’t hesitate to contact us by using the message button at the bottom of this page or the contact form.