It has been almost seven decades since the initial development of the first implantable cardiac pacemakers in the late 1950’s, with immense and rapid technological development subsequently leading to dramatic changes in the design and use of cardiac implantable electronic devices (CIED’s) around the globe.
The last two decades in particular have seen the introduction of leadless cardiac pacemakers, subcutaneous defibrillators, and more recently the development of tools for leadless endocardial left ventricular pacing and renewed interest in conduction system pacing.
Leadless Pacemakers
Leadless pacemakers were first introduced in their modern form in 2012, and currently commercially available options include the Medtronic Micra transcatheter pacing system and the Abbott AVEIR leadless pacing devices.
The first iteration of leadless devices were largely only ideal for patients that required only ventricular pacing and did not require or depend on atrioventricular (AV) synchrony.
Subsequent advances have greatly expanded the population of patients suitable for leadless pacing, including dual chamber systems (AVEIR DR) and a single chamber ventricular device capable of AV synchronous ventricular pacing (the Micra AV).
The Micra leadless pacemaker is a single chamber ventricular pacemaker, and current iterations include the Micra AV2 and Micra VR2, both of which utilize four nitinol tines for fixation. Median projected battery longevity for these devices is between 16 and 17 years.
Both devices have features typical of more traditional transvenous ventricular pacemakers, including accelerometer-based rate-adaptive pacing and automated capture threshold management. The Micra AV2 also allows for AV synchrony by detecting and sensing atrial contraction.
The Abbott AVEIR devices utilize a helix-based fixation mechanism, and like the Micra leadless pacemakers the devices are typically implanted using a delivery catheter via the femoral vein.
The AVEIR DR system allows for true dual chamber leadless pacing, and AV synchrony is achieved by wireless implant to implant communication.
Leadless pacemakers are generally associated with a significant reduction in complications typically associated with transvenous pacing systems, including device/lead infection, pocket hematoma, pneumothorax, lead failure, and lead dislodgement. Leadless pacemakers, on the other hand, are associated with a greater risk of vascular complications and pericardial effusion when compared with transvenous devices.
5-year follow up data is available for the Micra VR device, which includes data from 1809 patients. Outcomes and complication rates were compared to a reference population of transvenous pacemaker implants using a competing risk model. The major complication rate at 60 months post implant was 4.5%, which was significantly lower in comparison to the 8.5% major complication rate in the transvenous pacemaker group.
Importantly, there were no Micra removals due to infection throughout the 60 month follow period.
Future innovation will potentially allow for leadless conduction system pacing and integration with other CIEDs, such as subcutaneous defibrillators and endocardial left ventricular pacing systems.
Conduction System Pacing
Traditionally, right ventricular pacing is performed from the right ventricular apical septum, the consequence of which is highly dyssynchronous mechanical and electrical activation of both ventricles. Furthermore, right ventricular apical pacing can worsen clinical heart failure, result in a pacing-induced cardiomyopathy, and potentially worsen mitral and tricuspid regurgitation.
Several attempts have been made over the prior decades to either minimize right ventricular pacing or, more recently, to provide more physiologic pacing.
Early on, work was focused on pacing the His bundle since this results in proximal engagement of the intrinsic conduction system. Implantation success rates improved over the ensuing years with design of dedicated His bundle pacing delivery tools, but despite these additions procedural challenges remained.
These challenges resulted in interest in pacing at conduction system sites distal to the His bundle, specifically the left bundle branch area. Given the fairly wide arborizing elements of the left bundle branch in the septum, targeting this area is associated with a higher likelihood of procedural success.
Left bundle branch area pacing (LBBAP) must be distinguished from deep left ventricular septal pacing, which does not result in engagement of the intrinsic conduction system tissue.
In selective left bundle branch pacing the bundles/fascicles of the left bundle are captured exclusively, in contrast to non-selective left bundle branch pacing when both the left bundle and the adjacent myocardial tissue are engaged.
Interest in and adoption of left bundle branch area pacing has been growing rapidly over the past decade, and numerous studies have demonstrated excellent feasibility and safety. Dedicated delivery systems have further improved the rates of successful implantation, and both stylet-driven and lumenless pacing leads have been utilized successfully.
Left bundle branch area pacing is associated with reduced risk of mortality, hospitalization for heart failure, and upgrade to biventricular pacing when compared to right ventricular pacing.
There are currently several ongoing clinical trials evaluating the potential benefits of left bundle pacing, including PROTECT-HF, OptimPacing, and LEAP, in patients that have a bradycardia indication for pacing.
Observational studies and small randomized trials also suggest that LBBAP may be equivalent, or perhaps even superior to, biventricular pacing in patients that have an indication for cardiac resynchronization therapy. Larger randomized clinical trials evaluating this question are also currently underway.
Based on data then available, conduction system pacing received a class 2a recommendation in the 2023 HRS guidelines in those patients with an ejection fraction between 35 and 50%, who are anticipated to require frequent ventricular pacing.
References
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- Hrymniak, B, et al. Atrioventricular synchronous leadless pacing: Micra AV. Cardiol J. 2024 Feb 29;31(1):147–155.
- El-Chami M, et al. Leadless pacemakers at 5-year follow-up: the Micra transcatheter pacing system post-approval registry. Eur Heart J. 2024 Mar 1;45(14):1241–1251.
- Knops R, et al. A Dual-Chamber Leadless Pacemaker. N Engl J Med 2023;388:2360-2370.
- Cantillon D, et al. Wireless Communication Between Paired Leadless Pacemakers for Dual-Chamber Synchrony. Circ Arrhythm Electrophysiol. 2022 Jul;15(7):e010909.
- Whinnett Z, et al. Physiological pacing: mechanisms, clinical indications, and perspectives, European Heart Journal, Volume 46, Issue 35, 14 September 2025, Pages 3407–3419.
- Sharma, et al. Clinical outcomes of left bundle branch area pacing compared to right ventricular pacing: results from the Geisinger-Rush Conduction System Pacing Registry.
- Heart Rhythm 2022;19:3–11.
- Huang, Weijian et al. A beginner’s guide to permanent left bundle branch pacing
- Heart Rhythm, Volume 16, Issue 12, 1791 – 1796.
Michael Hoosien, MD
Dr. Michael Hoosien is a clinical cardiac electrophysiologist and director of the atrial fibrillation program at the Piedmont Heart Institute. Dr. Hoosien manages all aspects of electrophysiology and has a special interest in the management of atrial fibrillation.
