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Leadless Cardiac Pacing: Considerations for Patient Selection, Performance, Complications, Battery Longevity, End of Service, and Programming
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Any views and opinions expressed are those of the author(s) and/or participants and do not necessarily reflect the views, policy, or position of EP Lab Digest or HMP Global, their employees, and affiliates.
EP LAB DIGEST. 2023;23(9):20-21.
Since the introduction of pacemaker implantation more than 6 decades ago, tens of millions of patients with bradyarrhythmias and heart block have benefitted from the traditional transvenous pacemaker system. Traditional pacemaker components include a pulse generator and lead(s). Leadless pacemakers (LPs) are an emerging technology to circumvent complications related to a transvenous pacemaker. Additionally, LPs redefine patient experience by eliminating arm restrictions and offer no visible evidence of a pacemaker implantation.
Although conventional transvenous pacemaker therapy has evolved tremendously, significant complications still arise from pocket- and lead-related issues.1,2 An estimated 12.4% patients develop pacemaker complications within 2 months of implantation.1 Pocket-related adverse events include infection, hematoma, erosion, and cosmetic concerns (4.75%).1 Lead-related adverse events include fractures, insulation breaches, venous thrombosis and obstruction, and tricuspid regurgitation (5.5%).1 Other short-term complications include cardiac tamponade, pneumothorax, and lead dislodgement.3,4 Also, infections that lead to endocarditis and septicemia result in a high mortality rate and increase health care costs.5,6
Leadless pacing systems currently available in the United States include the Micra VR (Medtronic), Micra AV (Medtronic), and Aveir VR (Abbott). Recently, the Aveir dual-chamber leadless (DR) pacemaker system also received FDA approval.
Both Micra and Aveir VR are implanted using a minimally invasive approach via the femoral vein. Deflectable sheaths allow for delivery across the tricuspid valve into the right ventricle (RV). After the desired location is obtained, the pacemaker is deployed and secured by either nitinol tines (Micra) or by active fixation helix (Aveir VR). Both pacemakers are magnetic resonance (MR) conditional (1.5T and 3T) and both use a sensor to provide rate response (Micra uses a 3-axis accelerometer and Aveir VR uses a temperature-based sensor). Aveir VR has pre-fixation mapping capability by assessing current of injury, impedance, and pacing threshold, designed to help reduce the number of repositioning attempts after fixation.7 Comparison of the devices is detailed in the Table.
Several important factors should be addressed when considering leadless pacemaker technology. In this article, we review patient selection, performance, complications, battery longevity, end-of-service management, and programming options in current leadless pacing systems.
Patient Selection
Leadless pacing should be considered in patients without upper extremity venous access, Twiddler’s syndrome, a high risk of device infection or pneumothorax, or for patients on hemodialysis.8 Other patients include those who would otherwise receive a VVI pacemaker, such as those with permanent atrial fibrillation (AF) and atrioventricular (AV) block, or AF with a slow ventricular rate. Those with transient sinus arrest or AV block and a low anticipated ventricular pacing rate or inactive patients in sinus rhythm may also be potential candidates.9 The goal is to avoid pacemaker syndrome, development of pacing-induced cardiomyopathy (anticipated high ventricular pacing rate of >20%), and progression of heart failure.
Performance
The Micra IDE study was an international, multicenter, prospective trial to evaluate device safety and efficacy.10 Of 726 subjects, Micra implantation was successful 99.2% (n = 719). Serious adverse events occurred in 25 (3.4%) subjects, including cardiac perforations (1.5%), vascular complications (.3%), and venous thromboembolism (.3%).
The Micra Post-Approval Registry demonstrated 63% fewer complications than traditional pacemakers (n = 1817, 95% CI: .27-.52; P<.001).11 Furthermore, in >6000 Medicare patients, a comparison of 2-year outcomes of the Micra vs the transvenous VVI pacemaker showed a 38% lower adjusted rate of reintervention and 31% lower adjusted rate of chronic complications.12
Additionally, the LEADLESS II-Phase 2 trial was an international, multicenter study to evaluate safety and efficacy of Aveir.7 Of 200 subjects, implantation success was 98% (n = 196). Of the successful implants, 83.2% did not require repositioning. Serious adverse events occurred in 8 (4%) subjects, including cardiac tamponade (1.5%) and premature deployments (1.5%). Of those who underwent a successful implantation, 4 did not meet the capture threshold criteria and 4 failed the R-wave amplitude criteria, signifying that 95.9% (95% CI: 92.1%-98.2%) met the effectiveness performance goal.
The purpose of the Aveir DR i2i study was to evaluate the safety and efficacy of implantation of 2 devices in the patient population indicated for a DDD(R) pacemaker, maximizing true AV synchrony and expanding LP indications (Figures 1 and 2).
Complications
Transcatheter delivery systems with large-bore sheaths are becoming more common. To minimize groin complications, ultrasound-guided venous access and use of closure devices are encouraged. In patients with left bundle branch block, a temporary backup pacing wire may be considered. To avoid perforation, the optimal area of device deployment should be mid-septum (Micra) or the distal third of the septum (Aveir). The RV free wall and apex should be avoided. An analysis of 78% of all 96 deaths associated with Micra implantation were preceded by cardiac tamponade, mostly within the first hour after implantation.13 Therefore, pericardiocentesis capability or surgical intervention should be available. A risk score was developed to help determine predictors of pericardial effusion.14 The overall effusion rate was 1.1% and occurred more commonly in those age ≥85 years, body mass index <20 kg/m2, female sex, and chronic obstructive pulmonary disease. Repeat deployments were also associated with an increased risk of pericardial effusion in patients with elevated risk at baseline.
To prevent thromboembolism, intravenous heparin is given after obtaining venous access and advancing the delivery sheath. LPs can be performed with minimal interruption of anticoagulation, per physician’s discretion, and resumed same day >6 hours after the procedure.15
Other considerations include device dislodgement,16 which can be improved with enhanced physician training, deflection test, and electrical mapping prior to fixation.7
Rarely, implantation attempts are aborted due to patient anatomy, especially in those with significant scoliosis, creating an acute angle at the inferior vena cava-right atrial junction. Combined with a small cardiac size, the delivery system does not have the capability to safely prolapse into the RV, as compared to a conventional pacemaker lead (Figure 3, Video).
Battery Longevity/End-of-Service Management
Long-term follow-up is needed to confirm the projections used to determine battery longevity in leadless pacemakers. Aveir has an increased projected longevity, with the same battery chemistry (lithium carbon-monofluoride) as a standard transvenous pacemaker, larger size, and utilization of conductive telemetry. Signals are exchanged between electrodes on the skin and the implanted device in the ventricle in conductive telemetry. It is highly energy efficient, as it eliminates the need for an additional component (coil for electromagnetic coupling).17 Aveir is designed for chronic retrieval, with a designated tri-loop snare retrieval system and a success rate above 80% through 7 years regardless of implant duration.18
Micra uses radiofrequency telemetry for communication between the pulse generator and the programmer. It has a remote monitoring option via the CareLink system (Medtronic), which allows for monitoring of the battery/device status, electrical parameters, and for review of electrograms. A single-center study demonstrated that 7.6% of Micra implantations were discontinued at 3 years, secondary to cardiac resynchronization therapy upgrades, high threshold, temporary usage, battery depletion, and pacemaker syndrome.19 The pacing system can be turned off to allow for implantation of additional devices. The recommendation is that up to 3 Micra devices can be implanted in the RV.20 There is a proximal retrieval feature and by using a Goose Neck snare, successful retrieval has been shown after 4 years.21
Programming Options
Micra AV allows for VDD(R) pacing in patients who may benefit from maintenance of AV synchrony by accelerometer-based sensing of atrial contraction. The degree of AV synchrony varies in individual patients.22 The algorithm may be disturbed at higher heart rates or even upon standing due to atrial contraction undersensing. To minimize RV pacing and maximize device longevity, mode switch to VVI+ occurs during periods of intact AV conduction. Rate smoothing algorithms may overcome dropped beats due to atrial contraction undersensing.
Conclusion
Ongoing registry data and randomized controlled trials are needed to evaluate the long-term safety and effectiveness of leadless pacing systems, as compared with traditional devices.
Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. They report no conflicts of interest regarding the content herein. Dr Lo reports consulting fees and payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing, or educational events from Abbott.
References
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