Retrieval and replacement of a helix-fixation leadless pacemaker at 9 years post-implant

Leadless pacemakers (LP) are now established as a safe and effective alternative to traditional, transvenous pacemakers for single-chamber ventricular pacing.^, Although eliminating the transvenous pacing lead and pulse generator pocket may streamline LP delivery, long-term patient management may ultimately necessitate LP retrieval for device replacement or upgrade. LP retrieval may pose unique challenges, including the need to physically capture the device in motion during cardiac contraction, as well as potential fibrous encapsulation, which may impede this contact and the subsequent retrieval from the myocardium. As leadless devices are relatively new to the market, there is experience with the retrieval and replacement of LPs after a short or mid-term follow-up, but not after an extended time period.^{,  ,  ,}  This case report demonstrates the successful retrieval and replacement of a helix-fixation LP after a chronic implant duration of 9 years.

An 84-year-old woman with a body mass index of 21.6 kg/m² and long-standing, persistent atrial fibrillation (CHA₂DS₂-VASc score: 4) was being treated with anticoagulants (Pradaxa, 150 mg twice daily) and had received a single-chamber LP. This original helix-fixation LP (Nanostim LP), shown in Figure 1A, was implanted in the right ventricular (RV) apical septum without complication on December 17, 2012. At implant, the pacing capture threshold was 0.5 V at 0.4 ms pulse width, R-wave sensing amplitude 7.5 mV, and pacing impedance 500 Ω. Electrical measurements remained stable until 9 years post-implant, when the device failed to establish telemetry during routine follow-up in November 2021—indicative of the premature battery depletion issue associated with the October 2016 advisory. The patient fit the criteria for replacement with the single-chamber Aveir VR leadless pacing system (Abbott, Abbott Park, IL), also shown in Figure 1A. Distinctions between the 2 devices are described in the Discussion section.

One month later, on December 10, 2021, the patient underwent LP retrieval and replacement. The existing Nanostim LP was retrieved using the new Aveir Retrieval Catheter (Abbott, Abbott Park, IL). The retrieval catheter has similar operating principles and controls as a conventional steerable catheter, but has a high-torque design and is equipped with a tri-loop snare retrieval mechanism, docking cap, and protective sleeve at the distal end (Figure 1B). Note that although this catheter was designed for retrieval of the new Aveir LPs, the contact and torque transfer mechanisms of this retrieval catheter were designed to be backwards compatible with the proximal docking button of the Nanostim LP predecessor.

Retrieval of the original LP is summarized in Figure 2. With the open snare covered by the protective sleeve, the retrieval catheter was introduced via femoral venous access using the 25F Aveir Introducer and advanced up the peripheral vasculature to the junction of the right atrium and inferior vena cava. The protective sleeve was retracted and the catheter was advanced into the RV chamber under fluoroscopic guidance (Figure 2A). The fluoroscopic view most useful for both retrieval and implant was right anterior oblique 30^o, but anteroposterior and left anterior oblique 30^o are often used as complementary views to confirm coaxial alignment of the catheter and docking button. The radiopaque, tri-loop snare was positioned approximately 1 cm behind the proximal LP docking button (Figure 2B) to account for the forward nature of the closing mechanism and to avoid snaring the LP body. This maneuver was facilitated by the ability to independently actuate the catheter with the deflecting lever while adjusting the snare position with the snare control handle. The snare was closed around the docking button and then locked (Figure 2C). Coaxial alignment of the catheter to the LP was then created by gently pulling back on the retrieval catheter. The catheter docking cap was mated to the LP (Figure 2D) by separating the LP control handle from the main catheter handle, and the protective sleeve was then advanced halfway over the LP to facilitate coaxial catheter–LP alignment (Figure 2E). No resistance was noted as the protective sleeve was advanced over the LP.

With the LP docked and covered, the snare control handle was rotated counterclockwise 1 click at a time, and rotation of the radiopaque chevron on the LP was confirmed. The snare control handle was further rotated until the LP was visualized as free from the myocardium (Figure 2F–2I), and 3+ rotations of the chevron were confirmed. With the LP fully disengaged from the myocardium, the protective sleeve was advanced to fully cover the LP, and the catheter and mated LP were removed. In this particular case, intracardiac echocardiography was also used as a complementary visualization tool to (1) help guide snaring and (2) confirm the absence of pericardial effusion after LP removal. The time from retrieval catheter entrance into the RV chamber to LP capture and disengagement from the myocardium was under 2 minutes. The explanted Nanostim LP exhibited minimal fibrous tissue adhered to the LP case, with no signs of residual tissue on the docking button or fixation helix (Figure 2J). Of note, the operator had performed 42 such retrievals in the past.

Implantation of the new LP immediately followed Nanostim retrieval. The Aveir VR leadless device was implanted per usual manner using the Aveir Delivery Catheter, Aveir Loading Tool, and (existing) Aveir Introducer. The delivery catheter has a design that is consistent with the retrieval catheter, but is equipped with a distal tether mechanism rather than the tri-loop snare. Briefly, the LP was first tethered to the delivery catheter using the loading tool, in which the LP arrived prepackaged. The LP was then pulled in and fully docked to the delivery catheter docking cap, and the protective sleeve was advanced over the LP. The catheter and LP were advanced into the femoral vein through the existing introducer and fluoroscopically guided through the peripheral vasculature to the RV chamber. The time from myocardial disengagement of the first LP to introduction of the second LP into the RV chamber, including swapping the retrieval catheter with the delivery catheter, was 7 minutes.

Delivery of the replacement LP is summarized in Figure 3. The RV was first surveyed fluoroscopically using a contrast injection (Figure 3A). Once an acceptable RV apical site was selected, distinct from that of the previous LP, the protective sleeve was retracted (Figure 3B), and the catheter and LP were advanced to map electrical values for the new location. Next, the control knob was used to rotate the LP clockwise until complete helix-myocardium engagement (Figure 3C–3E), as evident by 1.25–1.5 rotations of the radiopaque LP chevron. The time from RV entrance to LP-myocardial engagement was also 7 minutes.

The LP was then released from the delivery catheter docking cap, with contact still maintained by the tethers (ie, tether mode, Figure 3F), thus allowing electrical assessment absent any force from the delivery catheter. A deflection test was performed to assess mechanical fixation and a commanded electrogram was recorded to assess the current of injury. Immediately after LP engagement, the pacing capture threshold (at 0.4 ms pulse width), R-wave sensing amplitude, and pacing impedance were 2.75 V, 7.5 mV, and 370 Ω, respectively. After a waiting period of 4 minutes for electrical stabilization, the pacing capture threshold, R-wave sensing amplitude, and pacing impedance were remeasured at 1.25 V, 9.0 mV, and 380 Ω, respectively. With the LP engaged at an acceptable location, it was released from the tethers using the LP release knob (Figure 3G), and the delivery catheter was removed. The entire LP retrieval and replacement procedure duration, from retrieval catheter in to delivery catheter out, was 36 minutes. The final LP position in shown in Figure 3H–3I. Furthermore, no acute complications were observed. Of note, the operator typically performs roughly 50 helix-fixation and 50 tine-fixation LP implants annually.

Prior to patient discharge the following morning, the pacing capture threshold, R-wave sensing amplitude, and pacing impedance were measured at 1.0 V, 8.5 mV, and 630 Ω, respectively.

The current paradigm shift from transvenous lead–based pacing to leadless pacing has been driven by several potential advantages. Eliminating the lead and pulse generator not only mitigates many of the associated complications, but also streamlines the implant workflow by alleviating the burden of selecting the proper lead length, managing excess lead slack, properly connecting the leads, and establishing and closing a subcutaneous generator pocket. A growing number of leadless pacemaker implants, however, will undoubtedly be followed by a demand for atraumatic retrieval and seamless device replacement. This case study demonstrated the successful retrieval of a chronically implanted, helix-fixation LP, followed in-line by replacement with a new helix-fixation LP. To the authors’ knowledge, this is the longest reported LP implant that was retrieved in humans to date.

Despite a 9-year implant duration, the predecessor Nanostim LP could be snared, docked, and unscrewed from the host myocardium in under 2 minutes from retrieval catheter entrance into the RV. Although the Aveir Retrieval Catheter used is currently the only commercially available tool indicated for such a task, alternative accessories have been used to assist past cases where LP orientation or tissue encapsulation made snaring more difficult (eg, guidewires, steerable ablation catheters, pigtail catheters).

The intact fixation helix and lack of remnant tissue observed, particularly at the distal fixation end, were notable and may be attributed to the use of torque, rather than tension, to disengage the helix from the host myocardium. The consistent designs of the retrieval and delivery catheters, along with their compatibility with the introducer, enabled a swift swap of the 2 catheters. Deployment of the new Aveir VR LP was also streamlined, with 7 minutes elapsing from RV chamber entrance to LP-myocardial fixation. Overall, the 36-minute total retrieval and replacement procedure duration are encouraging for the future of pacemaker patient management.

The 2 LPs used in this patient have several similarities and distinctions. Both are equipped with a similar distal helix fixation mechanism and central dome-shaped cathode. Both LPs interact with the delivery and retrieval catheters via proximal docking buttons, which allowed backward-compatibility of the retrieval catheter in this procedure, although the Aveir VR button has been redesigned to enhance catheter contact and minimize valve/tissue interactions. Furthermore, the Aveir VR was designed to be shorter in length than Nanostim (38.0 mm vs 41.4 mm) yet provide greater battery capacity (241 vs 219 mAhr), resulting in differences in diameter (19.5F vs 18F) and volume (1.1 cm³ vs 1.0 cm³). Importantly, Aveir VR was uniquely designed to be expandable, as an additional, atrial-specific Aveir LP may be able to be subsequently implanted and wirelessly paired with this ventricular Aveir LP for dual-chamber pacing, pending a successful pivotal trial (NCT05252702) and regulatory approval.

This case report demonstrates the successful chronic retrieval and replacement of a helix-fixation LP after a 9-year implant duration. The lack of complications and minimal procedure duration hold promise for lifetime patient management with helix-fixation leadless pacemakers.