Short-Term Safety and Performance of a Single-Chamber Leadless Pacemaker

A transvenous pacemaker (TVP) is first-line treatment for various bradyarrhythmias, but despite its effectiveness, there are major concerns because of serious complications in approximately 1 out of 8 patients over their lifetime.¹ These include acute complications, such as bleeding/hematomas, pneumothoraxes, pericardial effusions/perforations, infections, and lead dislodgements, and chronic complications such as lead fractures and infections, with a 3-fold increase in infection rates, especially during generator replacements.² Leadless pacemakers (LPs) have been developed to address some of the limitations associated with TVPs. Two LP systems are currently available for clinical use (Table 1) and both are inserted into the right ventricle via a femoral venous approach using a specially designed catheter-based delivery system. The Micra, developed by Medtronic, has been in use since 2013 and numerous prospective registries have evaluated its safety and feasibility.

Table 1.

Characteristics of Leadless Pacemakers

	Leadless pacemakers
	Micra transcatheter pacing system (Medtronic)	Aveir leadless cardiac pacemaker (Abbott Medical)
Dimensions, mm	25.9×6.7	38×6.5
Volume, cc	0.8	1.1
Weight, g	1.75	2.4
Battery longevity, years	12 (VR) 8–13 (AV)	10.3
Sheath size, Fr	27 OD/23 ID	27 OD/25 ID
Fixation mechanism	4 Nitinol tines	Helix
Automatic capture management	Available	N/A
MRI scan	Conditional (1.5T, 3T) Full-body	Conditional (1.5T, 3T) Full-body
Remote monitoring	Available*	N/A

*Manual transmission. AV, VDD mode; ID, inner diameter; OD, outer diameter; VR, VVI mode. Reproduced courtesy of Medtronic and Abbott Medical.

Article p 1809

In this issue of the Journal, Ando et al³ present the Micra Acute Performance (MAP) Japan study, which included 300 patients undergoing leadless VVI implants across 15 medical centers. MAP Japan is a prospective and observational study assessing the short-term safety and electrical performance of LP implantations in Japanese individuals. These patients are of particular interest because they may be at higher risk of the pericardial effusions characteristic of LP implantations due to their older age and smaller body size compared with Westerners.⁴ This study³ revealed a 100% success rate of the implantations. Additionally, the incidence of major complications was found to be 3.3%, encompassing issues such as thromboses, vascular access problems, pericardial effusions/perforations, and system revisions. That complication rate was comparable to previous investigations, namely the Micra Investigational Device Exemption study (3.86%)⁵ and the Micra Post-Approval Registry study (3.02%).⁶ The findings underscore the safety of the Micra LP, with minimal variations observed across different races and regions. Furthermore, the study demonstrated the electrical performance of the Micra device throughout the 12-month follow-up, as evidenced by a significant increase in the R-wave amplitude and decrease in the impedance, while the pacing threshold remained unaffected.³ Those observations are similar to previous reports.^5,6 Finally, the study revealed an improvement in frailty after implantation,³ aligning with the outcomes observed in the Japanese Heart Rhythm Society (JHRS) registry, which specifically investigated the favorable influence on functional capacity and its prognostic role in the context of TVP implantations.⁷

The literature has identified specific patient populations that may benefit significantly from LPs and these encompass patients with a high risk of an infection, those diagnosed with endstage renal disease, individuals with a history of previous device-related infections, and patients with anatomic constraints that complicate or prevent the use of transvenous pacing. Moreover, LPs are particularly advantageous for immunocompromised patients; patients undergoing radiotherapy, and those with congenital heart disease are also prime candidates for LPs.⁸ The recent Japanese Circulation Society (JCS) guidelines give a Class I, Level of Evidence B recommendation for VVI LPs as an alternative to TVPs in patients with symptomatic bradycardic atrial fibrillation, in whom venous access should be preserved, or in those with a venous occlusion or stenosis (Table 2).²

Table 2.

Recommendations and Evidence Levels for VVI Leadless Pacemakers

	COR	LOE	GOR (MINDS)	LOE (MINDS)
For patients with symptomatic bradycardia AF, in whom venous access should be preserved, or with venous occlusion or stenosis, VVI leadless pacemaker is recommended	I	B	B	III
For non-AF bradycardiac patients with condition that precludes the use of a transvenous pacemaker, including compromised venous access and the need to preserve venous access, VVI leadless pacemaker should be considered	IIa	B	C1	III
For patients who underwent CIED extraction due to infection and completed the antibiotic treatment, VVI leadless pacemaker may be considered	IIb	C	C1	IVa

AF, atrial fibrillation; CIED, cardiac implantable electronic device; COR, Class of Recommendation; GOR, Grade of Recommendation; LOE, Level of Evidence. (Adapted from Nogami A, et al. 2022.²)

LPs, in their initial functionality, operate in the VVI(R) mode. However, the 2nd-generation Micra transcatheter pacing system utilizes the atrial contraction signal obtained from the accelerometer to subsequently pace the right ventricle, thereby providing a VDD pacing mode. The system maintains AV synchrony approximately 70–90% of the time; however, this synchrony may be compromised during instances of high heart rates or during periods of intense physical activity.^9,10 Recently, Abbott Medical introduced a novel DDD leadless pacemaker, broadening its indications to patients with atrioventricular (AV) block.¹¹ Known as the Aveir leadless cardiac pacemaker system (Table 1), this innovative device is implanted in both the atria and ventricle, facilitating AV synchronization through bidirectional wireless communication with each heartbeat.¹¹ Multichamber LPs undoubtedly exhibit substantial potential, but the inherent operational and technical complexities are widely recognized.¹¹

Despite the advantages of LPs over TVPs,⁶ there remains a paucity of data concerning the retrievability and end-of-life (EOL) strategies for LPs. There are 2 options to address the EOL issue. Firstly, the LP can be left in place, and an additional device implanted adjacent to the non-functional LP. However, the presence of multiple devices in the heart may potentially compromise the cardiac function or introduce interference. The second strategy involves extracting the LP and subsequently implanting a new device. Early studies, as well as the MAP Japan study,³ have demonstrated the feasibility and safety of LP retrieval.¹² However, it is essential to acknowledge that a prolonged implantation may lead to the encapsulation of the device, making its extraction difficult or even impossible.^12,13

In summary, the current MAP Japan study³ showed the consistent safety of the Micra LPs, even in high-risk Japanese patients. There is no doubt that LPs represent a valuable option for specific patients. Ensuring proper training and peer supervision during the learning phase of the Micra LP implantation is critical to minimize acute vascular problems and pericardial effusion/tamponade, which are potentially fatal events associated with this procedure. It is important to emphasize that, unlike Europe and the USA, Micra LP implantations are permitted in Japan even in hospitals without cardiovascular surgery competence. As a result, the registration and release of safety information for all LP implantation cases overseen by the JHRS have even greater implications. Finally, long-term data will provide valuable insights into the device’s performance, durability, and potential complications that may arise with extended use.¹⁴

Conflicts of Interest

None.

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