Focus Issue: DevicesClinicalOptimizing atrial sensing parameters in leadless pacemakers: Atrioventricular synchrony achievement in the real world
Introduction
The leadless pacemaker (LPM) system was designed to overcome lead and pocket-related complications of conventional endovenous pacing devices. Several studies reported high rates of implant success and good safety profile with a reduction in major complications ranging from 48% to 60% when compared to patients with transvenous pacemaker.1,2 Therefore, LPM became an available option for patients with conduction system diseases with an increasing number of implants worldwide. However, when LPM were released, they only offered only single-chamber ventricular rate responsive pacing (VVIR mode) and they were mainly limited to patients with bradycardia and permanent AF, which accounts for about one-third of all pacing modes.3 In patients with normal sinus rhythm and high-degree atrioventricular (AV) block, AV synchronous pacing mode improves stroke volume, cardiac output, and quality of life and reduces the incidence of pacemaker syndrome and atrial fibrillation at long-term follow-up.4,5
The Micra AV feasibility studies evaluated the performance of a downloadable accelerometer-based atrial sensing algorithm in patients with AV block. Atrial sensing was feasible, and consequently, improved rates of AV synchrony (AVS) were found in patients already implanted with a single-chamber ventricular LPM after 30 minutes of algorithm performance.6 The MARVEL (Micra Atrial TRacking Using a Ventricular AccELerometer) 2 study demonstrated the feasibility of delivering AV synchronous pacing with an automated, enhanced accelerometer-based algorithm (MARVEL 2 algorithm) downloaded to the Micra VR LPM (Medtronic, Inc, Minneapolis, MN) for up to 5 hours. More than 95% of patients with AV block had >70% of AVS at rest, and the percentage of AVS increased from 26.8% during VVI pacing to 89.2% during VDD pacing. Nevertheless, manual reprogramming of the atrial sensing parameters were required in 40% of patients and AVS decreased to 69.8% during the standing position and also while normal or fast walking.7
These studies were conducted in patients with already implanted Micra devices and over a short time period. Therefore, the performance of the accelerometer-based algorithm in de novo patients implanted with the new Micra AV LPM (Medtronic, Inc, Minneapolis, MN) and undergoing daily activities is unknown, and standard recommendations on reprogramming of the atrial sensing parameters to achieve an optimal AVS are also lacking.
We aimed to study the performance of the MARVEL 2 algorithm in a cohort of patients newly implanted with the Micra AV LPM. We tried to assess the programming changes needed to achieve P wave tracking, to assess the usefulness and accuracy of the device counters, and finally, to maximize the percentage of AVS the device can provide during daily activities.
Section snippets
Study design
This was a nonrandomized, prospective, single-center study of patients implanted with the Micra AV LPM. The study adhered to the Helsinki Declaration as revised in 2013, and the local institutional bioethics committee approved the research protocol. All patients agreed with the study protocol and provided their informed consent.
Patient selection and procedures
Consecutive patients with AV block who met class I or II guideline-based indication for ventricular pacing only8 undergoing successful Micra AV implantation were
Population characteristics
Between June 2020 and November 2021, 32 patients underwent successful Micra AV implantation, of whom 31 (96.9%) remained in VDD mode at some visit throughout follow-up and 26 (81.3%) remained in VDD mode in all visits. Baseline characteristics and implant-related data are displayed in Table 1. The median fluoroscopy time was 3.9 minutes, and the median procedure time, from femoral puncture to femoral suture, was 21 minutes.
Atrial sensing parameter reprogramming
Manual reprogramming of the atrial sensing parameters was needed in all
Discussion
Several findings can be extracted from our population of patients implanted with the Micra AV LPM under real-world conditions:
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As the auto-setup test is performed at rest, the algorithm may not provide proper tracking of the whole range of sinus rates the patient can experience.
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A4 signal undersensing due to an excessive prolongation of the automatic A3 window was the most common issue after the auto-setup test. Although it has already been reported that shortening of the A3 window end has a
Conclusion
High AVS in outpatients with LPM can be feasible, although it may require close follow-up and frequent manual reprogramming, especially at the beginning. Among all the programmable parameters, the A3 window end modification seems to be the keystone to achieve this goal, along with proper patient selection. Moreover, AVS estimated with the device counters seems to be reliable as the usual tool for follow-up.
Acknowledgments
Special thanks to Gonzalo Sánchez MSc, for his help and selfless work.
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Funding Sources: This research did not receive any grant from funding agencies in the public, commercial, or not-for-profit sectors.
Disclosures: Drs Briongos-Figuero and Estévez-Paniagua report personal fees from Medtronic and Boston Scientific. The rest of the authors report no conflicts of interest.
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Drs Briongos-Figuero and Estévez-Paniagua are co-first authors.