Leadless Atrial Pacing Targeting Bachmann's Bundle for Atrial Resynchronization

Abstract

Background

Leadless pacemakers have transformed pacing by reducing risk for infection and lead-related complications. The feasibility of achieving leadless Bachmann's bundle area pacing (BBAP) for atrial resynchronization is not known.

First-in-Human Summary

A 49-year-old woman with sinus node dysfunction and interatrial conduction delay underwent leadless atrial pacemaker targeting Bachmann's bundle (BB). Using intracardiac echocardiography and electrographic mapping, the pacemaker was positioned at the BB region. Reduced right atrium–to–lateral left atrium conduction time and paced P wave duration were confirmed.

Discussion

Right atrial appendage pacing may exacerbate interatrial conduction delay and promote atrial fibrillation. BBAP using a leadless atrial pacemaker, in contrast, has been shown to enhance atrial synchrony.

Novelty

This case demonstrates the first-in-human permanent implantation of a leadless pacemaker in the BB area, providing a strategy for leadless atrial resynchronization.

Take-Home Message

Leadless BBAP may offer a physiological approach to atrial conduction system pacing by improving atrioventricular dromotropy and reducing subsequent risk for atrial fibrillation.

Graphical Abstract

In recent years, there has been a surge of interest in conduction system pacing (CSP) as a means to prevent pacing-induced ventricular dyssynchrony and cardiomyopathy. CSP also provides an alternative to biventricular pacing for cardiac resynchronization therapy in patients with dyssynchronous cardiomyopathy from conduction block. Similarly, atrial CSP via Bachmann's bundle (BB) pacing has been proposed as a means to restore physiological atrial activation, reduce interatrial conduction delay (IACD), and reduce the risk for subsequent atrial fibrillation (AF).1, 2, 3, 4, 5, 6 BB pacing has been shown to improve atrial synchrony and conduction, reversing electrocardiographic markers predictive of AF.⁷

Take-Home Messages

• •Leadless BBAP may offer a physiological approach to atrial conduction system pacing by improving atrioventricular dromotropy.
• •Leadless BBAP may reduce subsequent risk for atrial fibrillation.

Although ventricular CSP has previously been reported with leadless pacing systems, the feasibility of leadless atrial pacing targeting BB for atrial resynchronization has not been established. We report the first-in-human case of a leadless atrial pacemaker implanted at the BB site, confirmed with invasive electroanatomical mapping and demonstrating objective evidence of atrial resynchronization and feasibility of this novel approach.

Case Description

A 49-year-old woman with a history of sinus node dysfunction presented for leadless atrial pacemaker implantation. Her medical history was notable for rheumatic heart disease and paroxysmal AF, mitral valve repair, and tricuspid valve repair in 1996, followed by mechanical mitral valve replacement, repeat tricuspid valve repair, left atrial (LA) appendage exclusion, and a surgical maze procedure in 2015. She had a history of hypertension and symptomatic sinus bradycardia, with mean heart rate of 45 beats/min. Her baseline 12-lead electrocardiogram is shown in Figure 1. Low-amplitude P waves with a duration of 213 ms and a superiorly directed axis were noted. Given her sinus node dysfunction, prolonged and superiorly directed P waves indicative of BB delay, history of AF, and history of valve replacement, an active fixation leadless atrial pacemaker was selected for BB area implantation to reduce the risk for infection, with upgrade capability in case greater ventricular pacing burden was needed.

Figure 1.

Baseline 12-Lead Electrocardiogram

The procedure was performed under fluoroscopic and intracardiac echocardiographic guidance. First, an Advisor HD grid (Abbott Medical) multipolar electrode high-density mapping catheter was used to create a voltage map of the right atrium (RA) and the distal coronary sinus and to identify endocardial BB potentials at the junction of the superior RA and superior vena cava (SVC) (Figure 2A). The mapping catheter was also advanced to the right and left pulmonary arteries in an attempt to identify and pace epicardial BB signals; these regions, however, demonstrated significant low voltage scar and inability to capture, likely as a result of the prior epicardial maze surgery. A decapolar catheter was then advanced deeply into the coronary sinus to the level of the anterolateral LA for electrographic recordings (Figure 2B). A NUVISION 4-dimensional intracardiac echocardiographic catheter (Biosense Webster) was positioned in the RA for visualization of the RA, LA, SVC, RA appendage (RAA), and interatrial septum (Figure 3). A pigtail catheter was used to perform contrast-enhanced fluoroscopic imaging of the SVC and superior RA, facilitating identification of the endocardial BB region (Figure 4). Baseline conduction measurements were performed during sinus rhythm, showing a P-wave duration 196 ms, a PR interval of 211 ms, and P-wave onset–to–lateral LA (LLA) conduction time of 181 ms (Figure 5A). The multipolar catheter was placed in the RAA, where the paced P-wave duration was notably prolonged at 328 ms, the paced PR interval was 345 ms, and the RAA stimulation–to–LLA interval was 301 ms (Figure 5B). The multipolar catheter was then positioned in the endocardial BB position at the RA-SVC junction, where the paced P-wave duration was 181 ms, the paced PR interval was 202 ms, and the BB stimulation-to-LLA interval was 136 ms.

Figure 2.

Electroanatomical Map and Fluoroscopy of the Right Atrium and Coronary Sinus

(A) Electroanatomical map of the right atrium, Bachmann's bundle (BB), right atrial appendage (RAA), and coronary sinus (CS) with catheter. (B) Fluoroscopy of multielectrode catheter in the RAA and decapolar catheter in the distal CS.

Figure 3.

Intracardiac Echocardiography of Right Atrium

(A) 2-dimensional intracardiac echocardiography (ICE) of the right atrium (RA) identifying the RA appendage (RAA) and superior vena cava (SVC). (B) 4-dimensional ICE of the RA identifying the RAA and SVC.

Figure 4.

Atriogram of Right Atrium

(A) Atriogram of Bachmann's bundle region in right anterior oblique projection. (B) Atriogram of Bachmann's bundle area in left anterior oblique projection.

Figure 5.

12-Lead and Intracardiac Measurements

P-wave, PR interval, and time to lateral left atrium during sinus rhythm (A), right atrial appendage (RAA) pacing (B), and Bachmann's bundle (BB) pacing (C). CSD = distal coronary sinus.

A leadless atrial pacemaker was advanced via the right femoral vein into the RA and positioned at the BB area at the position identified with electroanatomical mapping. After device deployment, sensing at this location was found to be low. The device helix was withdrawn and repositioned slightly inferiorly using intracardiac echocardiography (ICE) to ensure that the device was still targeting the BB area. Pace mapping from the leadless atrial pacemaker demonstrated paced P-wave duration of 181 ms, a paced PR interval of 225 ms, and a leadless atrial pacemaker stimulation–to–LAA interval of 134 ms (Figure 5C). The local electrogram at the BB site confirmed appropriate positioning (Figure 6A). Pacing from this location also revealed earlier activation at the distal coronary sinus, consistent with BB area pacing (BBAP). Given the evidence of BB capture, the leadless atrial pacemaker was implanted using its active fixation helix delivery system, following standard implantation techniques (Figure 6B). ICE (Figure 7) and fluoroscopy (Figures 8A to 8D) were used to guide deployment. Postimplantation pacing at the BB area confirmed the shortened P-wave duration, PR interval, and stimulation–to–LA conduction time observed during preimplantation mapping. Two-dimensional and four-dimensional ICE verified stable device fixation (Figure 9) without obstruction of the atrial septal fossa (Figure 10). The patient tolerated the procedure well without complications.

Figure 6.

Leadless Atrial Pacemaker Electrogram

(A) Electrogram of leadless atrial pacemaker sensing at Bachmann's bundle. (B) Electrogram of injury current following active fixation of leadless atrial pacemaker at Bachmann's bundle. AS = atrial sense.

Figure 7.

Intracardiac Echocardiographic Guidance of Leadless Atrial Pacemaker to Bachmann's Bundle Target Site

BB = Bachmann's bundle.

Figure 8.

Fluoroscopy of Leadless Atrial Pacemaker Implant

Fluoroscopic images of the leadless atrial pacemaker implant at Bachmann's bundle site in right anterior oblique (RAO) tether mode (A), left anterior oblique (LAO) tether mode (B), RAO final position (C), and LAO final position (D).

Figure 9.

Intracardiac Echocardiography of Leadless Atrial Pacemaker Implant

(A) 2-dimensional intracardiac echocardiographic (ICE) images of atrial leadless pacemaker (PM) at Bachmann's bundle implantation site. The star denotes the helix deep in Bachmann's bundle. (B). 2-dimensional and 4-dimensional ICE images of leadless atrial PM at Bachmann's bundle implantation site. SVC = superior vena cava.

Figure 10.

Postimplantation Intracardiac Echocardiographic Image of Atrial Fossa

LA = left atrium; RA = right atrium.

Discussion

This case demonstrates the feasibility of leadless atrial pacing targeting the BB area for atrial resynchronization. Traditional atrial pacing sites such as the RAA often worsen rather than improve atrial synchrony because RAA pacing worsens instead of improving IACD. P-wave duration has been shown to be an independent predictor of AF. Additionally, atrial pacing at the RAA has been shown to increase AF compared with pacing in the BB.⁸

At baseline, the patient exhibited significant sinus node dysfunction and BB delay, as demonstrated by the prolonged, fractionated, and very low amplitude P wave. Temporary pacing in the RAA demonstrated marked worsening of baseline IACD. Prior to leadless atrial pacemaker implantation, the endocardial BB area was localized using electroanatomical mapping, fluoroscopy, and ICE. In doing so, accurate implantation at the BB area could be verified anatomically and electrically. This site was verified by intracardiac pace mapping as well. Reductions in P-wave duration, PR interval, and conduction time to the LLA were demonstrated when leadless atrial pacemaker pacing from the BB area was compared with sinus rhythm. Additionally, when comparing leadless atrial pacemaker pacing from the BB area with the RAA pacing site, a marked reduction in interatrial conduction time was observed. These improvements seen during pacing at BB suggest successful atrial resynchronization compared with sinus rhythm by overcoming significant BB conduction delay, illustrating potential advantage of BB pacing compared with RAA pacing. Additionally, the use of ICE demonstrated the safety of the technique as well as avoidance of obstruction of the septum to allow future transseptal access if needed.

Prior studies of BB pacing have primarily used endocardial or epicardial leads, requiring transvenous or surgical approaches. This case provides the first known description of a leadless atrial pacemaker successfully implanted at the BB site, demonstrating safe, effective atrial resynchronization. As the mainstay of BBAP will likely be in the use endocardial leads, leadless atrial pacemakers provide an alternative for patients with increased lead and pocket infection risk. Additional techniques, such as electroanatomical mapping and four-dimensional ICE, were useful to demonstrate proof of concept in this first-in-human case report but may not be required for future practical BBAP. A simplified approach with emphasis on safety using ICE and confirmation of electrical capture by inspection of changes in atrioventricular dromotropy on surface electrocardiography may be sufficient. It remains to be seen if long-term putative benefits of BBAP, such as reduced AF burden, are realized for this patient given her history of rheumatic heart disease and prior multiple valve procedures. Future studies comparing outcomes of leadless BB and RAA pacing are needed.

Conclusions

This case highlights the first-in-human experience of implantation of a leadless atrial pacemaker targeting the BB area and confirmed with LA recording. This technique demonstrates improvements in IACD compared with either sinus rhythm or RAA pacing. Traditional atrial pacing, particularly from the RAA, has been associated with IACD, which may contribute to AF progression. In contrast, BB pacing has the potential to restore physiological atrial activation and reduce AF burden. By using a leadless system for this approach, we anticipate a reduced risk for infection and potential use in a wider range of clinical settings.

Funding Support and Author Disclosures

Dr Hollis is a consultant for Abbott, Boston Scientific, and Medtronic. Dr Ryu is an Abbott employee, Senior Director, R&D Clinical Engineering and Applied Research. Dr Sabet is an Abbott employee, Director of Product Development. Dr Upadhyay has provided consulting, speaking, and scientific advising for Abbott, Biotronik, Boston Scientific, GE Medical, Medtronic, Philips BioTel, Rhythm Science, and Zoll Medical. Dr Atwater is an advisory board member for Medtronic; and is a consultant for Medtronic, Bristol Meyers Squibb, Pfizer, Abbott, and Biosense Webster. Dr Yang has reported that she has no relationships relevant to the contents of this paper to disclose.