Leadless pacemakers: The future of pacing?

P. Vijay Shekar^*

Department of Cardiology, Kauvery Heart City, Trichy, Tamilnadu, India

*Correspondence: Tel.: +91 96864 69004; email: [email protected]

“The best way to predict the future is to create it”

As we look back at the history and evolution of pacemakers, permanent pacemakers were indicated for diseases of the cardiac conduction system that could disrupt normal conduction pattern and can result in symptomatic bradycardias. Pacing was developed using external devices and alternating current, which subsequently evolved to “wearable” transistorized battery powered pacemakers. A paradigm shift occurred with the introduction of the entirely implantable pacemaker systems.

The current standard of care is the transvenous pacing system, which consists of a can (pulse generator) and the lead. The can (pulse generator) houses the battery and pacemaker circuitry, and is implanted pre pectorally in the infraclavicular region. Leads which contain the conductor coils – remain in contact with myocardial tissue through distal electrodes. The tip of the leads (which contain the electrodes) are positioned in the right ventricle and/or the right atrium through the subclavian or axillary vein approach. The proximal end is connected to the pulse generator. The number of leads may vary according to the type and mode of the pacemaker function-single chamber, dual chamber and biventricular pacing (cardiac resynchronisation therapy).

Transvenous pacing is not without complications. Complication rates may vary between 1-6%, which include access site, pocket site and lead related complications. The subclavian or axillary vein being the common approach, is associated with risk of pneumothorax, haemothorax and inadvertent arterial puncture. Pocket site infection and hematoma are not uncommon and may require revision and re-exploration.

Lead related complications can occur early or late after implantation and has been identified as the “Achilles heel” of the transvenous pacing system. Lead dislodgements (0.5%) and cardiac perforation (0.4%), though rare can occur in the immediate post implant period. Late complications which include pacemaker malfunction due to lead conductor fractures, insulation breaks and tip mineralization may warrant re do procedure. Infective endocarditis, lead related tricuspid regurgitation and venous obstruction are also known to occur. Lead related infective endocarditis could result in poor outcomes, with mortality rates of 12-30%.

With evolving technology to improve outcomes and safety of pacing systems, eliminating the lead will substantially reduce the complication rates. This led to the development of leadless pacing systems. Leadless pacing systems aim to reduce the pocket site and lead related complications.

Two leadless pacing systems are currently available: the Micra transcatheter Pacing system (Medtronic) and the Nanostim Leadless Cardiac Pacemaker (St. Jude Medical). The Micra Trancatheter pacing system was FDA approved in 2016 and is available in India.

Micra Transcatheter Pacing system is the currently available “smallest pacemaker” and 93% smaller than the conventional pacemaker. The pacing electrode along with battery and circuitry is encased inside a single unit which measures around 0.8 cm3. The Micra device is available as Micra VR and Micra AV system.

The leadless pacing system is supported with sufficient clinical data regarding its safety and efficacy. A recent report from the Micra study compared matched cohorts of transvenous pacemakers, demonstrating 48% lower complications and 47% less hospitalizations at one year, driven by an 82% decrease in pacemaker revision procedures in the Micra group. Though early complications like lead dislodgements and perforation were similar in both groups, much of the benefit was derived by minimising pocket related complications and late lead related complications.

Fig. 1. Leadless pacemaker system. Left: Micra Transcatheter Pacing system (Medtronic) and Right: Nanostim Leadless Cardiac Pacemaker (St. Jude Medical).

How is a leadless pacemaker implanted?

The leadless pacemaker requires a separate delivery system and cable. The device is delivered through large bore femoral vein access. Using a 27 F delivery sheath, the pre-mounted device (on a steerable delivery cable) is tracked through the inferior vena cava into the right atrium. The device is tracked across the tricuspid valve into the right ventricle and positioned in the RV mid septum or RV apex. The distal end of the device has tines which anchors to the myocardium. After confirming position under fluoroscopy and ensuring device anchorage, the device is released from the delivery system.

Is the leadless pacemaker solution for all?

Though the leadless pacemaker minimizes complications, its major limitation is its ability to pace and sense a single chamber- function as a single chamber pacemaker. This functionality limits the benefit of the leadless pacemaker to a select subset of patients. The indications in the current scenario includes patients who require single chamber pacing (patients with atrial fibrillation) and have contra indications or higher complication rates with conventional pacemaker implantation. A patient who has recurrent pocket site infection/lead related infection or venous obstruction involving the SVC and its connections will ideally benefit from leadless pacing system.

The recent introduction of Micra AV pacing system overcomes the limitations to a certain extent. The Micra AV device has additional algorithms, by which it can sense atrial mechanical activity and synchronise with ventricular contraction, establishing AV synchrony. The device dimensions and implantation technique remain the same.

Leadless pacemakers have shown promise in potentially reducing complications associated with transvenous systems. Though conventional transvenous pacing still remains the standard of care, advances in technology can help evolve this form of cardiac pacing to benefit more patients.

“The future awaits”

References

Mulpuru SK, Madhavan M, McLeod CJ et al. Cardiac pacemakers: function, troubleshooting, and management: Part 1 of a 2-Part series, J Am Coll Cardiol. 2017 ;69(2):189-210.
El-Chami MF, Merchant FM, Leon AR. Leadless pacemakers. Am J Cardiol. 2017;119:145-8.
Roberts PR, Clementy N, Al Samadi F et al. A leadless pacemaker in the real-world setting: The micra transcatheter pacing system post-approval registry. Heart Rhythm. 14:1375-9.
Tjong FVY, Reddy VY. Permanent leadless cardiac pacemaker therapy. A comprehensive review. Circulation 2017;135:1458-70.
Cantillon DJ, Exner DV, Badie N, et al. Complications and health care costs associated with transvenous cardiac pacemakers in a nationwide assessment. JACC Clin Electrophysiol. 2017;3:1296-1305.

Dr. P. Vijay Shekhar
Consultant Cardiologist

Leadless pacemakers: The future of pacing?