For over fifty years, cardiac pacing systems have been surgically implanted for symptomatic bradycardia (Reynolds et al., 2016). Approximately 200,000 pacemakers are implanted annually in the United States, and due to an aging population and increasing pacing indications, this number is expected to grow (Bhatia & El-Chami, 2018). While these devices are effective, approximately one in eight patients has an early complication, usually related to the transvenous lead or subcutaneous pocket. These complications include pneumothorax/hemothorax, cardiac perforation, lead dislodgement/integrity problems, pocket infections/hematomas, endocarditis, vascular obstructions, and tricuspid regurgitation (Reynolds et al., 2016 and Bhatia & El-Chami, 2018). Pacemaker technology has rapidly advanced in the pursuit of decreasing complications and improving outcomes.
Leadless pacemakers were first proposed in the 1970s and finally gained FDA approval in 2016 (Bhatia & El-Chami, 2018). They are miniature leadless pacing systems that are small enough to be placed inside the heart and avoid the need for a subcutaneous pocket and transvenous leads, the weakest aspects of a traditional pacemaker (van der Zee & Doshi, 2016 and Reynolds et al., 2016). The leadless pacemaker is dime-sized, free-standing, and inserted via femoral venous access. The pacemaker is affixed to the right ventricular myocardium and released. The delivery system is then removed, and the pacemaker remains embedded in the right ventricle (van der Zee & Doshi, 2016). Currently, there are two systems available: the Micra (Medtronic) and the Nanostim (St. Jude). The Micra received FDA approval in 2016 and the Nanostim is still awaiting approval (Bhatia & El-Chami, 2018). The Micra is fixated to the myocardium utilizing four self-expanding nitinol tines and the Nanostim contains a screw-in helix that penetrates about 1 mm into the myocardium (van der Zee & Doshi, 2016). The leadless pacemakers have a battery longevity of ten years, which is comparable to traditional devices, and are capable of VVI or VVIR (ventricular demand pacing where only the ventricle is paced, sensed, and the pulse generator inhibits pacing output in response to a sensed ventricular event) pacing only.
Although the leadless pacemaker is a relatively new technology, the preliminary reports of long-term performance and complications are promising, including low complications, few system revisions, and stable pacing parameters. These exciting new devices are not for all patients, however, and are contraindicated in those who require dual-chamber pacing, who have existing cardiovascular implantable electronic devices, mechanical tricuspid valves, pulmonary hypertension, or inferior vena cava (IVC) filters (van der Zee & Doshi, 2016).
While the future appears to be bright for these tiny devices, there are some concerns, including chronic right ventricular pacing due to single-chamber pacing, potentially leading to atrioventricular and mechanical dysfunction and heart failure (Bhatia & El-Chami, 2018). Other noted drawbacks include the need for larger venous access tools for delivery, limited safety data from nonrandomized studies, and estimated but unproven longevity of the device. (Reynolds et al., 2016).
Leadless pacing offers an innovative and safe alternative for cardiac pacing in patients who require single-chamber pacing while avoiding the common pitfalls of traditional transvenous pacemaker systems. Future avenues of development in this specialized area are boundless and include transforming kinetic energy from cardiac motion to fuel the pacemaker, wireless left ventricular pacing system, potentially utilizing leadless pacemakers with subcutaneous defibrillators, and the development of a leadless pacemaker with dual-chamber pacing capabilities and resynchronization therapy (van der Zee & Doshi, 2016 and Bhatia & El-Chami, 2018).
Bhatia, N., & El-Chami, M. (2018). Leadless pacemakers: a contemporary review. Journal of Geriatric Cardiology, 15, 249-253. doi:10.11909/j.issn.1671-5411.2018.04.002
Reynolds, D., Duray, G., Omar, R., Soejima, K., Neuzil, P., Zhang, S., ...Ritter, P. (2016). A Leadless intracardiac transcatheter pacing system. New England Journal of Medicine, 374, 533-541. doi: full/10.1056/NEJMoa1511643
Van der Zee, S., & Doshi, S. (2016, May 23). Permanent leadless cardiac pacing. Retrieved from https://www.acc.org/latest-in-cardiology/articles/2016/03/23/08/09/permanent-leadless-cardiac-pacing