The Art of Leadless Pacing: Insight Into Leadless Implantation From a Community Hospital

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EP LAB DIGEST. 2024;24(9):1,8-11.

Evangelos A Diamantakos, DO, FHRS, FACC, FACOI
Clinical Cardiac Electrophysiology; Desert Cardiology – Eisenhower Medical Center, Rancho Mirage, California

Electrophysiologists today are fortunate to practice in an evolving era of cardiac pacing with recent innovations occurring in the field of leadless pacing. The groundwork for cardiac pacing began with Albert Hyman in the 1930s via a hand-cranked generator that delivered electrical current via a needle electrode to the right atrium intercostally.¹ Then, the first myocardial wire for post-operative pacing was performed by C Walton Lillehei in 1957, followed by the first implantable pacemaker with rechargeable battery performed by Rune Elmqvist and Ake Senning in 1958,1,2 and 2 years later, with the implantation of a battery-powered pacemaker using a myocardial lead by William Chardack.² In the 1970s, the concept of leadless pacing was brought to the forefront by J William Spickler et al involving a totally self-contained intracardiac pacemaker.³ From its inception, leadless technology has undergone an evolution involving reconfiguration of device concepts and components, pacing algorithms, and expansion to dual-chamber leadless pacing. 

Transvenous cardiac pacemakers are traditionally composed of an extravascular pulse generator and intravascular leads that are fixated to the endocardial surface. The complications that can arise from transvenous implants often involve the leads and can include: (1) stress and fracture of the leads from repetitive mechanical motion; (2) substrate for infection and bacterial growth; (3) thrombogenicity; (4) impingement of the tricuspid valve leaflets causing valvular dysfunction; and (5) extraction difficulty when clinically indicated.⁴ For reasons such as these, leadless pacemakers were developed. Commercially, ² leadless pacemakers are available: the Micra transcatheter delivery system (Medtronic) and AVEIR (Abbott) leadless pacemakers. The Micra transcatheter delivery system encompasses Micra VR and AV devices. The Micra VR leadless pacemaker is a single-chamber ventricular leadless pacemaker that can be used for patients suitable for ventricular demand pacing,⁵ while the Micra AV leadless pacemaker can be used in patients who have indication for AV synchrony by utilizing an AV synchrony algorithm. Similarly, the AVEIR leadless pacemakers have a VR device that is also indicated for ventricular demand pacing, but have recently developed an AR device to treat those with sinus node dysfunction and intact AV and intraventricular conduction alone, or to be paired with a VR device for complete dual-chamber leadless pacing in patients with this indication. While there are differences in delivery system mechanics, fixation (active fixation tines versus active fixation helix), and releasing mechanisms, leadless pacemaker are safe to implant with low risk and successful outcomes.

Patient Selection

In our practice, identifying patients for leadless pacing is conducted in a stepwise fashion. It begins by recognizing patient characteristics favorable for leadless implantation and assessing the risk factors that could lead to complications. Age may affect implant decision and should be used in assessing complication risk. For most older patients, active or disabled, leadless pacing may be a great choice based on pacing indications (noted below), especially if there is an infrequent need for ventricular pacing, helping to minimize the complications that could arise from transvenous pacing. Some studies have identified that an age ≥85 can be a risk factor for complication during leadless implant.⁶ However, a recent article by Hofer et al assessing safety of leadless pacemakers in octogenarians reported major complication rates at 2.7% during a 5-year follow-up between patients ≥80 and <80 years of age, demonstrating similarly low complication rates with safety and efficacy for leadless implant in octogenarians.⁷ It has been our experience that leadless pacemakers can successfully be implanted in all age groups, including those >80 years of age, without complication.  
 

Following patient assessment, factors that favor leadless implant include those with limited venous access (ie, hemodialysis patients), a prior history of bacteremia or infective endocarditis, are immunocompromised,⁸ current indwelling catheters,⁸ physical disability, undergoing transcatheter aortic valve replacement (TAVR) with risk for developing complete heart block, or active infection requiring transvenous lead extraction who are pacemaker dependent. Patients who undergo thoracic radiotherapy, are of young age, or may have congenital heart disease without appropriate venous access for transvenous pacing should also be considered.⁸ Implanting physicians will ultimately aim to mitigate the risk of infection, and leadless technology offers this advantage over transvenous devices with marked reduction in pacemaker-related infection (7%-12%), which can increase with replacement procedures.⁹ Other perceived advantages may include patient preference, less implant and recovery time, lack of ipsilateral arm restrictions following implant, lack of device scar, and lack of pocket hematoma or pneumothorax. As patients are identified, risk factors and contraindications for leadless implantation should be individually assessed. Aside from age, risk factors can include female gender, low body weight (body mass index <20 kg/m2), chronic obstructive pulmonary disease,⁷ and no prior median sternotomy. 

Pacing indications must then be identified once the patient has been clinically assessed. Single-chamber leadless pacing indications encountered in our practice include: (1) sinus node dysfunction with symptomatic, intermittent tachycardia-bradycardia syndrome; (2) symptomatic sick sinus syndrome without a high burden of right ventricular (RV) pacing; (3) paroxysmal atrioventricular block; (4) post TAVR with complete heart block and normal ventricular function; (5) and atrial fibrillation (AF) or atrial flutter with slow ventricular response. With the availability of dual-chamber leadless pacing, this can serve as an alternative to transvenous pacing for those exhibiting sick sinus syndrome, chronic, symptomatic second- and third-degree atrioventricular (AV) block, symptomatic bilateral bundle branch block, or single-chamber atrial pacing indicated for sinus node dysfunction and normal AV and intraventricular conduction systems.

There is no right or wrong decision in choosing one single-chamber leadless device over the other. Leadless pacing can be tailored to each patient based on these indications. Below are 3 examples of leadless implantation at our institution: 

Case 1. A 69-year-old female with symptomatic paroxysmal AF despite rate control medication and class 3 antiarrhythmic medication (amiodarone) presented with symptomatic tachycardia-bradycardia syndrome, resulting in multiple conversion pauses, the longest lasting 12 seconds with presyncope. She was emergently sent to the emergency department (ED), where a temporary transvenous pacemaker was placed until timing for a dual-chamber leadless pacemaker could be coordinated. Figure 1 demonstrates AVEIR DR leadless pacemaker placement.

Case 2. A 77-year-old female presented with symptomatic high-degree AV block in the setting of hyperkalemia and underwent temporary transvenous pacing. Once the hyperkalemia was corrected, the patient did not appear to demonstrate any further pacing requirements, and the temporary transvenous pacemaker was removed. Over the next 24 hours, she developed intermittent episodes of high-degree AV block despite normalized potassium levels and without other reversible causes. The patient underwent Micra AV2 implant (Figure 2). 

Case 3. A 77-year-old obese male with a past medical history of diabetes, peripheral venous disease, and AF presented after a syncopal event at home, with an unknown down time of approximately 6 hours. When he awoke and was able to contact emergency medical services, he was brought to the ED with a heart rate of 30 beats per minute in AF with complete heart block and left bundle branch escape, which subsequently developed into slow ventricular response with longest RR interval of 7.7 seconds and right bundle branch escape. The patient was taken for leadless pacemaker implantation with the AVEIR VR leadless pacemaker (Figure 3). 

Troubleshooting
Based on our experience implanting primarily single-chamber leadless pacemakers, we offer the following implantation and troubleshooting techniques for peripheral venous anatomy as well as right atrial and RV anatomy:  

1. Tortuous peripheral venous anatomy. In our practice, we do not routinely perform peripheral venogram but have when wire advancement under fluoroscopy was difficult. In these circumstances, after obtaining right common femoral vein access via micropuncture access and ultrasound guidance, a micropuncture sheath is inserted and contrast is injected to visualize ipsilateral venous anatomy. If right-sided venous anatomy appeared severely tortuous and cannot accommodate the outer sheath, left femoral vein access is obtained and these steps for venogram are performed. If left-sided venous anatomy is suitable, left-sided access is maintained and implant is performed. 

2. Internal jugular vein approach. In patients where femoral vein access is contraindicated, such as the presence of inferior vena cava filter, chronic common femoral vein deep vein thrombosis, anatomical constraints such as small right atrial size, difficult tricuspid valve crossing, or mechanical tricuspid valve, an internal jugular approach can be considered safe and successful for implantation.^10-13 Studies have shown successful implantation with utilizing both leadless pacemaker systems demonstrating less non-apical implants, early ambulation for patients, and with safety and efficacy.^10-13 Internal jugular access can be safely attempted given the experience and comfort of the operator.

3. Delivery system orientation to optimize tricuspid valve crossing and septal positioning. Crossing into the RV can be difficult, but the following tips can successfully navigate a difficult tricuspid valve crossing. With RV implants, device position is visually assessed on fluoroscopy to be just above the superior vena cava and right atrial junction. Then, we begin deflecting across the tricuspid valve with counterclockwise rotation of the delivery sheath to cross anteriorly through the valve. Advancing the outer sheath over the delivery system can also help provide support when attempting to cross the valve. There are rare instances that a higher approach is warranted but could be used; be extremely cautious to prevent the sheath from popping across the tricuspid valve in a superior-to-inferior trajectory. It is also important to use the left anterior oblique (LAO) view to aid in coaxial trajectory across the valve. Once across the tricuspid valve, remove all deflection and allow the delivery system to be directed towards the right ventricular outflow tract (RVOT), as this is an anatomically septal structure. We believe starting in this location allows for less entrapment in the tricuspid valve apparatus, which may hinder septal trajectory with clockwise rotation. Slight deflection from the RVOT with initial clockwise rotation should position the device in septal orientation, but should be confirmed in the LAO view. Individualize LAO orientation for each patient, as this is not always reproducible and is dependent on heart rotation. Furthermore, delivery sheath orientation can best be visualized in the LAO view, as the deflected portion of the sheath will appear foreshortened across the tricuspid valve, with the tip of the sheath oriented in the mid RV cavity. In this position, a quick fluoroscopic assessment will provide spatial reference of the septal aspect of the tricuspid valve (TV), which could sometimes act as a negative fulcrum point to prevent septal position with continued clockwise rotation, orientating the sheath parallel to the septum with the tip of the delivery system directed to the anterior wall in the LAO view. If this occurs, 2 techniques can be performed: (1) counterclockwise rotation of the whole system to remove the fulcrum point off the septal aspect of the tricuspid valve annulus, which may direct the tip of the sheath septal; or (2) counterclockwise rotation to neutral position, slightly pulling back on the delivery system and reapproaching septal orientation with clockwise rotation. In our experience, the LAO 40-degree view should individualize septal position for most patients. 

4. The importance of right anterior oblique (RAO) view. While the LAO view will define septal positioning, the RAO view will help identify TV clearance and help define “RAO space”¹⁴ with contrast injection to avoid the anterior RV recess and prevent cardiac perforation. Also, as described by Li et al,¹⁵ contrast injection in the RAO view will help define basal, mid, and apical positioning by subdividing the RV into 9 zones to avoid apical placement and optimize implant in a mid-septal position correlating with zone 2 of the ventriculogram (Figure 4). In our practice, we use an RAO 30 view to obtain these results. 

5. Releasing mechanism. For Micra release, once adequate tine engagement has been assessed, it is important to flush the system with normal saline prior to release. Once a floss technique of the suture is performed, the more “resistant” end is cut and slow pull back of the suture is performed. If any resistance is felt, a continued slow pull, along with using cardiac contraction during pull, will allow for safe release and less stress on the tines, which could result in dislodgement. For the AVEIR releasing mechanism, we have found that assessing coaxial alignment in LAO view and slight upward deflection of the sheath in RAO view with synchronized sheath-tether-distal button movement during the cardiac cycle will allow for optimal release of the device. A flush prior to release can help eliminate any contrast remaining in the system that may make release difficult. If release of the device does not occur, advancement of the protective sleeve near the docking cap may aid in providing support for device release. 

Final Thoughts
What does the future hold for leadless pacing? Atrial leadless pacing may become appealing for first-line pacing in those with sinus node dysfunction and intact AV nodal conduction, with the ability to upgrade to a dual-chamber leadless system in the future if AV block occurs. Dual-chamber leadless pacing will likely continue to refine pacing algorithms to maximize battery longevity, and we may even see upgrades in battery longevity in either device. We do believe the time is upon us where leadless pacing and extravascular implantable cardioverter-defibrillators may become more common for patients.¹⁶ The thought of dual-chamber leadless pacing integration with leadless biventricular pacing is also exciting and findings from the SOLVE-CRT study appear promising for leadless biventricular pacing.¹⁷ Lastly, leadless pacemakers have become safe to extract when acute dislodgement is suspected, high thresholds have occurred requiring replacement, upgrade to a transvenous system is now indicated, or elective replacement indicator has been reached.¹⁸ Initial data presented by Beurskens et al demonstrated safety in extracting both Micra and Nanostim (Abbott, predecessor to AVEIR) with successful retrieval reported at >75% between both devices.¹⁸ Success has been demonstrated with retrieval of a 7-year-old Micra leadless pacemaker¹⁹ as well as multiple case studies demonstrating the safety in retrieving AVEIR leadless pacemakers^20-21 even after 9 years post implant.²² As more experience for retrieving leadless pacemakers has evolved²³ and a dedicated retrieval catheter designed for the AVEIR leadless pacemakers has been developed, successful retrieval has been demonstrated at >88% long-term retrieval success.²⁴ It is an exciting time to practice in electrophysiology as technology continues to evolve. The future of leadless pacing is bright. 

Disclosure: Dr Diamantakos has completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. He reports consulting fees from Abbott for Heart Rhythm advisory board on leadless pacing (2024) and telephone call on leadless discussion (2024).

Find the author on X at: @HISrefrPVC

References

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16. Boston Scientific initiates trial to evaluate industry’s first modular CRM system. Boston Scientific. Published December 2, 2021. Accessed July 15, 2024. https://news.bostonscientific.com/2021-12-02-Boston-Scientific-Initiates-Trial-to-Evaluate-Industrys-First-Modular-CRM-System

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23. Afzal MR, Jamal SM, Son JH, et al. Tips and tricks for safe retrieval of tine-based leadless pacemakers. J Innov Cardiac Rhythm Manag. 2021;12(6):4562-4568. doi:10.19102/icrm.2021.120606

24. Reddy VY, et al. Worldwide experience with leadless pacemaker retrievals: a worldwide Nanostim experience out of 9y. Presented at: APHRS 2022; Nov 18-20, 2022; Singapore.