Implant, performance, and retrieval of an atrial leadless pacemaker in sheep

doi:10.1016/j.hrthm.2020.09.022

Heart Rhythm

Volume 18, Issue 2, February 2021, Pages 288-296

https://doi.org/10.1016/j.hrthm.2020.09.022 Get rights and content

Background

Medtronic is developing an atrial Micra Transcatheter Pacing System (Medtronic, Minneapolis, Minnesota) and associated retrieval system.

Objective

The purpose of this study was to evaluate chronic atrial Micra retrieval, reimplantation, and chronic pacing performance.

Methods

Sheep were implanted in 2 groups: group 1 (n = 6) for 6 months, a second device implanted, and first retrieved and studied for an additional 6 months; group 2 (n = 6) for 6 months, devices were retrieved, and a second device implanted and observed acutely. Both groups underwent histopathological evaluation. Pacing capture thresholds (PCTs), p wave amplitude, and pacing impedances were measured chronically. Device retrieval times were recorded, and intracardiac echocardiography was used.

Results

At 24 weeks, PCTs for group 1 were low and stable for both the first device (0.55 ± 0.14 V) and the second device (0.57 ± 0.09 V), in which the average retrieval time was 17:35 minutes. For group 2, the average retrieval time was 6:12 minutes, chronic PCTs in the first device were 0.53 ± 0.11 V, and acute PCTs for the second device were 0.71 ± 0.19 V. Pathological findings were within an expected range of tissue responses for similar Micra acute and chronic implants and device retrievals. p waves and impedances were stable and within an expected range for implant site and electrode design. Complications included 1 early dislodgment and 1 death attributed to a prototype retrieval tool.

Conclusion

In an animal model, an atrial Micra can be easily implanted with excellent chronic pacing performance and is easily retrievable at 6 months. A second device can successfully be implanted with low, chronic stable thresholds. A developed prototype retrieval tool was easy to use and, with modifications, complication free.

Introduction

Pacemaker leads are the “Achilles’ heel” of pacing and defibrillation systems. Leadless pacemakers eliminate lead fractures and pocket-related issues, help avoid venous occlusions, and have the potential to reduce lead endocarditis. Studies have demonstrated that implantation of a ventricular Micra is feasible and safe.¹^,² At 0.8 mL volume, the Micra is 93% smaller than a traditional pacing system with an estimated battery longevity of 12 years.²^,³ In comparison to traditional systems, there are 63% fewer major complications and in addition capturing 23.9% of patients not felt to be candidates for a traditional transvenous pacemaker placement.¹ Considerable patient satisfaction has been attributed to the absence of a subcutaneous pocket.

The second generation Micra that provides atrioventricular synchrony has expanded the eligible patient population that can be treated with leadless pacemakers.⁴ However, there is a limitation to ventricular only placement. It is a natural step to expand the benefits for leadless pacing to patients with sinus node dysfunction. Placement of a miniaturized pacer in the atrium has its own unique challenges.

Section snippets

Methods

We evaluated in a sheep model the fixation of a leadless pacemaker(s) with a unique set of tines designed for attachment in the atrial architecture (Figure 1A). Evaluation was based on the validity and performance of acute and chronic implanted atrial Micra devices, the ability to implant a second atrial Micra within the right atrial (RA) appendage, the feasibility of retrieving a chronically implanted atrial Micra, and pathological changes.

Atrial Micra devices were implanted transvenously in 6

Results

One early gross dislodgment occurred in group 1 within 24 hours of implantation. That animal was included in acute but not chronic analysis. The animal with dislodgment was replaced with another for a total of 6 animals with device 1 in both group 1 and group 2. In group 1, 4 animals received a second chronic device (device 2). All remaining animals (group 2) had acute implants for device 2. There were 2 early deaths in group 1. One had an early termination after the second procedure due to an

Discussion

It is reasonable to believe that the beneficial features of leadless pacemakers can be extended to atrial pacing. Past studies demonstrate that 36% of patients may be candidates for an atrial pacer alone.5, 6, 7 However, there are unique biomedical and engineering challenges of atrial leadless pacing. The atrial Micra shares engineering features with the ventricular Micra (ie, battery, pacing electrodes, and main device body), but others are unique such as the fixation mechanism for the thin

Conclusion

In an animal model, an atrial Micra device can be easily implanted with excellent early and chronic pacing performance. The atrial Micra device is easily retrievable at 6 months. A second device can successfully be implanted with low, chronic stable thresholds. Complications occurred with 1 implant and 1 retrieval and reflect the unique challenges of placement of an atrial leadless pacemaker. Work is ongoing to improve the implant technique. A developed prototype retrieval tool was easy to use

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Cited by (13)

Cardiac Implantable Electronic Devices in the Fontan Patient
2022, Canadian Journal of Cardiology
Citation Excerpt :
Leadless atrial pacing, using small footprint devices that can undergo endothelialization, may permit transvenous pacing for atriopulmonary and lateral-tunnel Fontan patients, potentially reducing the long-term thromboembolic risk. Such technologies are in development.80 Likewise, use of emerging technologies based on the conversion of ultrasonic energy to local myocardial stimulation may even permit upgrade to CRT through a nonsurgical transcatheter approach.81
As a result of remarkable progress in operative techniques and cardiology care during childhood, Fontan patients continue to age and require team-based multidisciplinary expertise to manage complications encountered in adulthood. They face particular challenges in terms of altered hemodynamic stressors, cardiac and hepatic failure, and arrhythmias. Arrhythmias in Fontan patients are highly prevalent and associated with underlying anatomy, surgical technique, and postoperative sequelae. Diagnostic tools, treatments, and device strategies for arrhythmias in Fontan patients should be adapted to the specific anatomy, type of surgical repair, and clinical status. Great strides in our understanding of arrhythmia mechanisms, options and techniques to obtain access to relevant cardiac structures, and application of both old and new technologies have contributed to improving cardiac implantable electronic device (CIED) therapies for this unique population. In this state-of-the-art review, we discuss the various arrhythmias encountered in Fontan patients, their diagnosis, and options for treatment and prevention, with a focus on CIEDs. Throughout, access challenges particular to the Fontan circulation are considered. Recently developed technologies, such as the subcutaneous implantable cardioverter defibrillator, carry the potential to be transformative but require awareness of Fontan-specific issues. Moreover, new leadless pacing technology represents a promising strategy that may soon become applicable to Fontan patients with sinus-node dysfunction. CIEDs are essential tools in managing Fontan patients, but the complex clinical scenarios that arise in this patient population are among the most challenging for the electrophysiologist treating patients with congenital heart disease.
En raison des progrès remarquables accomplis en matière de techniques opératoires et de soins cardiologiques pédiatriques, les patients qui ont subi l’intervention de Fontan continuent d’avancer en âge et ont besoin d’une expertise multidisciplinaire pour gérer les complications qu’ils rencontrent à l’âge adulte. Ces patients doivent composer avec des difficultés particulières ayant à voir avec la modification des facteurs de stress hémodynamique, l’insuffisance cardiaque et hépatique, et les arythmies. Ces dernières sont très fréquentes chez les patients ayant subi l’intervention de Fontan et se trouvent associées à l’anatomie sous-jacente, à la technique chirurgicale et aux séquelles postopératoires. Les outils diagnostiques, les traitements et les stratégies technologiques visant à remédier aux arythmies chez les patients ayant subi l’intervention de Fontan devraient être adaptés aux ca-ractéristiques anatomiques individuelles, au type de réparation chi-rurgicale et au tableau clinique. Les grandes avancées sur le plan de notre compréhension des mécanismes de l’arythmie, les options et les techniques dont nous disposons pour accéder aux structures cardiaques d’intérêt, de même que la mise en œuvre de technologies an-ciennes et nouvelles ont contribué à améliorer les traitements faisant appel à des dispositifs cardiaques électroniques implantables (DCEI) dans cette population unique. Le présent article dresse un bilan exhaustif de la question. Nous y abordons les diverses formes d’a-rythmies qui touchent les patients ayant subi l’intervention de Fontan, leur diagnostic et les options de traitement et de prévention, en accordant une attention toute particulière aux DCEI. Les problèmes d’accès que pose la circulation de Fontan sont pris en compte tout au long de notre article. Les technologies récemment mises au point, comme le défibrillateur cardioverteur implantable sous-cutané, pourraient être porteuses de changements profonds, mais elles nécessitent une prise de conscience des problèmes qui se rattachent à l’intervention de Fontan. En outre, la nouvelle technologie de stimulation sans sonde se révèle une stratégie prometteuse qui pourrait bientôt devenir applicable dans les cas de dysfonctionnement du nœud sinusal chez les patients ayant subi l’intervention de Fontan. Les DCEI sont des outils essentiels pour la prise en charge des patients ayant subi l’intervention de Fontan. Cependant, les scénarios cliniques complexes observés au sein de cette population de patients font partie de ceux qui posent le plus de difficultés aux électrophysiologistes qui traitent les patients atteints de cardiopathies congénitales.
Preclinical safety and electrical performance of novel atrial leadless pacemaker with dual-helix fixation
2022, Heart Rhythm
Citation Excerpt :
Taken together, these electrical metrics demonstrate stable LP–myocardial contact and the ability to provide effective pacing and sensing without the variability that can negatively impact battery longevity. The electrical metrics were similar to a recent report of Micra™ LPs (Medtronic, Minneapolis, MN) implanted in the RA of 12 sheep at 24 weeks (PCT 0.6 ± 0.2 V; sensing amplitude 4.3 ± 1.3 mV; impedance 415 ± 60 Ω).7 Independent evaluations of gross pathology at study termination revealed no evidence of helix disengagement or device dislodgment, no clinically significant tissue perforation, no adverse interactions with valves or atrial walls, and no infection.
Complications associated with transvenous pacemakers, specifically those involving the lead or subcutaneous pocket, may be avoided with leadless pacemakers (LPs). The safety and efficacy of single-chamber right ventricular LPs have been demonstrated, but their right atrium (RA) use poses new design constraints.
The purpose of this study was to evaluate the implant success, electrical performance, and safety of a novel RA LP design in benchtop and preclinical studies.
A new LP was designed with a dual-helix fixation mechanism specific to the RA anatomy. A 12-week preclinical ovine study was conducted to evaluate implant success, electrical performance, mechanical stability, and safety in vivo, with supporting benchtop measurements to quantify the mechanical forces needed for device retrieval and dislodgment.
LPs were successfully implanted in all 10 ovine subjects with no complications. The pacing capture threshold improved significantly over time from implant to week 12 (1.1 ± 0.7 V vs 0.4 ± 0.2 V, P = .008). Sensing amplitudes and pacing impedances were stable from implant to week 12 (4.8 ± 1.8 mV vs 6.0 ± 1.9 mV, P = .160; and 393 ± 77 Ω vs 398 ± 65 Ω, P = .922, respectively). Gross pathology and microscopic histology revealed no adverse interactions and no evidence of device dislodgment or clinically significant myocardial perforation. Benchtop ex vivo porcine atrial tissue measurements revealed greater pull forces required to dislodge the LP vs transvenous active fixation lead (0.42 ± 0.18 lbf vs 0.29 ± 0.08 lbf, P = .020), and greater rotational forces required for deliberate extraction (0.28 ± 0.04 lbf vs 0.14 ± 0.07 lbf, P <.001).
The novel atrial LP demonstrated successful implantation, with acceptable electrical performance, mechanical stability, and safety in a 12-week preclinical study.
Leadless atrioventricular synchronous pacing in an outpatient setting: Early lessons learned on factors affecting atrioventricular synchrony
2022, Heart Rhythm
Citation Excerpt :
Whether atrial mechanical sensing will prevail in leadless PMs remains debatable. Because atrial leadless pacing is already on the horizon,18 other methods for ultra-low-power wireless device synchronization may gain attention as they might improve AV synchronization.19,20 Programming adequate atrial sensing parameters can remain challenging.
Leadless pacemakers (PMs) capable of atrioventricular (AV) synchronous pacing have recently been introduced. Initial feasibility studies were promising but limited to just a few minutes of AV synchronous pacing. Real-world, long-term data on AV synchrony and programming adjustments affecting AV synchrony in outpatients are lacking.
The purpose of this study was to investigate AV synchrony and influences of PM programming adjustments in outpatients with leadless VDD PMs.
All patients who received a leadless VDD PM (Micra™ AV, Medtronic) between July 2020 and May 2021 at our center were included in this observational study. AV synchrony was assessed repeatedly postoperatively and during follow-up using Holter electrocardiographic (ECG) recordings. AV synchrony was defined as a QRS complex preceded by a p wave within 300 ms. The impact of programming changes during follow-up on AV synchrony was studied.
A total of 816 hours of Holter ECG from 20 outpatients were analyzed. During predominantly paced episodes (≥80% ventricular pacing), median AV synchrony was 91% [interquartile range (IQR) 34%–100%] when patients had sinus rates 50–80/min. Median AV synchrony was lower when patients had sinus rates >80/min [33% (29%–46%); P <.001]. During a stepwise optimization protocol, AV synchrony could be improved (P <.038). Multivariate analysis showed that a shorter maximum A3 window end (P <.001), lower A3 threshold (P = .046), and minimum A4 threshold (P <.001) improved AV synchrony.
Successful VDD pacing in the outpatient setting during higher sinus rates is more difficult to achieve than can be presumed based on initial feasibility studies. The devices often require multiple reprogramming to maximize AV sequential pacing.
Leadless pacemakers: A review of current data and future directions
2021, Progress in Cardiovascular Diseases
Citation Excerpt :
Furthermore, LPs that can deliver atrial, multi-chamber, and physiologic pacing are in development and will expand the use of LPs. Recent data evaluated the performance of an atrial Micra in sheep.64 This Micra is a modified version of the existing ventricular Micra, with shorter and flatter tines to minimize perforation risk in the right atrium, a chamber with even thinner walls than the RV.
Leadless pacemakers (LPs) have revolutionized the field of pacing by miniaturizing pacemakers and rendering them completelty intracardiac, hence reducing complications related to pacemaker pockets and transvenous leads. However, first generation LPs appear to be associated with a higher rate of myocardial perforation as compared to transvenous pacemakers (TV-PPM). Currently, LPs are predominantly designed to pace the right ventricle with no LPs that provide atrial or biventricular pacing. In this article, we review the available data on LPs while advocating for the need for a randomized controlled trial comparing LPs to TV-PPMs. In addition, we review the future directions of leadless devices.
Swine models in translational research and medicine
2024, Veterinary Pathology
The Micra Transcatheter Pacing System: past, present and the future
2023, Future Cardiology

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: Funding sources: This work was supported by Medtronic.

: Disclosures: Dr Eggen, Ms Hilpisch, Mr Drake, Mr Grubac, Mr Anderson, Mr Colin, Mr Seifert, Dr Mesich, and Dr Ramon are employed by and have ownership interest in Medtronic. Dr Vatterott has consulted for Medtronic, Philips, Inspire, Cook, and Boston Scientific.

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ExperimentalImplant, performance, and retrieval of an atrial leadless pacemaker in sheep

Background

Objective

Methods

Results

Conclusion

Introduction

Section snippets

Methods

Results

Discussion

Conclusion

Heart Rhythm

Heart Rhythm

JACC Clin Electrophysiol

Int J Cardiol Heart Vessel

A leadless intracardiac transcatheter pacing system

N Engl J Med

Ventricular pacing or dual-chamber pacing for sinus-node dysfunction

N Engl J Med

Minimizing ventricular pacing to reduce atrial fibrillation in sinus-node disease

N Engl J Med

Experimental
Implant, performance, and retrieval of an atrial leadless pacemaker in sheep