EP Perspectives

Thoughts on the Development of a Completely Implantable Epicardial Leadless Radiofrequency Pacemaker System: Then and Now

Todd J. Cohen, MD

Department of Medicine

NYU Winthrop Hospital

Mineola, New York

Todd J. Cohen, MD

Department of Medicine

NYU Winthrop Hospital

Mineola, New York

In 1979, I was fortunate to be able to participate in the Newark Beth Israel Medical Center’s summer externship program. This program was organized by Dr. Victor Parsonnet, the hospital’s director of surgery and an innovator in the development of the transvenous pacemaker as well as one of the founders of the North American Society of Pacing and Electrophysiology (NASPE), the predecessor of the Heart Rhythm Society. I was assigned, as described in my acceptance letter by Dr. Parsonnet, “to a project on development of a leadless pacemaker” under the supervision of Dr. George Myers and Mr. Todd Rodgers. The results of that summer research project demonstrated the feasibility of a totally implantable epicardial leadless radiofrequency (RF) pacemaker system. In vitro experiments were used in determining parameters to be used in a definitive version. The transmitter and receiver were constructed, encapsulated, and prepared for implantation. In vivo experiments included acute experiments involving two dogs. In the first experiment, the pacemaker system was tested revealing a constant pacing output, via critical coupling, and 3.0 percent transmission efficiency at a 0.5 cm separation of the transmitter and receiver. The dog was paced for approximately 15 minutes using a myocardial bipolar screw-in electrode. The second experiment studied both the pacing threshold and the possible placement of the transmitter on the diaphragm. This type of pacemaker would eliminate the problems of metal fatigue, coil migration, and coupling variance while taking full advantage of long-life power sources. 

Since the inception of the transvenous pacemaker, the pacing lead has been described as the weak link in the system. Prevalence of lead-related issues has increased as device implantations have become more common.1 In conjunction with lead failure, associated complications in both leaded pacemakers and implantable cardioverter-defibrillators (ICDs) include device infection and vascular complications, while techniques to offset these issues include lead and device extraction.2-5 Leadless pacing systems have recently emerged as an alternative to their leaded counterparts, offering freedom from lead complications; however, some of these systems (manufactured by companies besides Medtronic) remain under investigation with respect to their clinical efficacy in normal and abnormal hearts.6,7 

The original manuscript, entitled “The Development of a Completely Implantable Epicardial Leadless Radiofrequency Pacemaker System,” which to my knowledge was never published, details one of the earliest versions of a leadless pacing system. This project and the resultant manuscript was my first foray into the field of electrophysiology and cardiac rhythm management, while these fields were still in their infancy. I had finished my sophomore year of college at Johns Hopkins University, and was able to apply my biophysics background to build a transmitter and receiver in order to eliminate the lead from the pacing system. The transmitter LRC circuitry as well as a screw-in electrode-receiver were designed, built, tested, and encapsulated in Silastic® by myself. As part of the project, the team demonstrated that RF impulses could be wirelessly transmitted from the transmitter to the receiver in order to provide pacing impulses to the heart without using a lead (conductor), an entirely novel concept with respect to implantable devices back then. Wireless communication of any type, to and from implantable pacemakers, was not yet invented. After in vitro testing of the leadless pacing system, an in vivo implant in a canine model was performed by Dr. Parsonnet, in which he successfully demonstrated the system’s ability to pace. 

Following completion of this research project, the paper was one of two finalists in Newark Beth Israel Medical Center’s Summer Externship Research Competition, placing second in the competition. While dated in some ways by today’s standards, this paper provides details on a very early leadless pacing system prototype that attempted to physically eliminate the lead between the pacemaker’s pulse generator and pacing electrode. In essence, the pulse generator sent RF impulses over a short distance to a pacing electrode receiver attached to the myocardium. The manuscript’s conclusions were based on available data at the time. The leadless pacemaker developed then is quite different than currently approved leadless pacemaker technologies. 

The 1979 RF system demonstrated an early proof of concept, but had the need for close coupling between the transmitter and receiver in order to effectively pace the heart. Although the receiver electrode was implanted in the epicardium and the transmitter was implanted beneath the sternum, an endocardial receiver implant could theoretically be performed, with a much smaller and thinner device, and with a subcutaneous subcostal RF pacemaker pulse generator transmitter in close proximity to the receiver. 

The complete elimination of the hard-wired pacing lead using a radiofrequency-based transmitter-receiver system comes with an entirely different set of problems. This system would be vulnerable to electromagnetic interference, which if implanted in a pacemaker-dependent patient, could potentially result in catastrophic failure to pace. Such a system would require a strong firewall as well as encryption technologies to ensure uninterrupted delivery of the transmitted impulse to the receiver without interference. Perhaps, this system would be better suited for providing the left ventricular pacing component of a cardiac resynchronization device. A left ventricular receiver electrode could be deployed in the coronary sinus vein (or one of its branches) or on the left ventricular epicardium through a minimally invasive approach.

In the 21st century, complete electromagnetic interference prevention would be a significant hurdle for any RF-based transceiver system due to the plethora of devices vying for limited RF bandwidth. Nearly three decades after this project, wireless communication from the programmer to an implantable device has become standard. Even with this advancement, pacemaker vulnerability has been highlighted by recent pacemaker firmware updates in order to sure up vulnerability to hacking. In addition, it should be noted that the ideal mechanism of secure wireless communication between two or more implantable devices has not yet been fully refined. Since this original project, transvenous pacemaker and defibrillator leads have continued to be the leading source of device failure. This is highlighted by two large defibrillator lead recalls in 2007 and 2011, both of which led to tremendous oversight and intervention in order to provide remediation. Other efforts are focusing on implementing these devices in more patient populations and with less device-related complications as well as with quicker postsurgical recovery than that seen with traditional pacemakers.8-10

Although we have come far in the field of leadless pacing, there are still a number of steps that need to be taken before this technology can be freely used in the general population. For example, although another modern leadless pacing system under development yielded promising results, it was not without controversy.11,12 To date, only one manufacturer (Medtronic) has an FDA-approved system that is commercially available in the United States. Furthermore, present technology can only be used for single-chamber ventricular pacing and is therefore not indicated in patients who would benefit from a dual-chamber system. Also, because the technology is relatively new, its cost is higher than that of traditional leaded pacemaker systems. In addition, a paucity of long-term data on its safety and efficacy exists, with a limited number of nonrandomized clinical trials having been performed to date. Implantation techniques have been associated with a 2.3% incidence of groin puncture site events plus cardiac perforation or effusion.10 Despite these complications, leadless pacing may ultimately be more beneficial for patients in terms of its removal of the possibility of lead-related complications. 

When we worked on this leadless pacemaker project in 1979, oscilloscopes were the norm and personal computers were not readily available. Figure 1 is from a 1979 newspaper article showing me working in front of one of these oscilloscopes, building basic circuitry with wires, capacitors, resistors, and other elementary electronic equipment. There was no easily available computer-based signal processing, circuitry design, and/or three-dimensional printing for device development. Pacemaker-sensing algorithms were circuit based, not written in code. 

We have seen vast improvements in the EP field, including the development and wide acceptance of ICDs, CRTs, MRI-safe devices, and catheter ablation procedures (both with RF and the cryoballoon). Even with all these advances, we await more data and research on the ideal configuration of leadless pacemaker technology, and look forward to its continued use in clinical practice.

Disclosure: The author has no conflicts of interest to report regarding the content herein.  

References

  1. Escher DJ. Types of pacemakers and their complications. Circulation. 1973;47(5):1119-1131.
  2. Borek PP, Wilkoff BL. Pacemaker and ICD leads: strategies for long-term management. J Interv Card Electrophysiol. 2008;23(1):59-72.
  3. Bongiorni MG, Segreti L, Di Cori A, et al. Overcoming the current issues surrounding device leads: reducing the complications during extraction. Expert Rev Med Devices. 2017;14(6):469-480.
  4. Gomes S, Cranney G, Bennett M, Giles R. Lead extraction for treatment of cardiac device infection: a 20-year single centre experience. Heart Lung Circ. 2017:240-245.
  5. Koneru JN, Kaszala K, Huizar JF, Ellenbogen KA. Lead fracture: incidence, diagnosis and preventing inappropriate ICD therapy. Card Electrophysiol Clin. 2011;3(3):409-420.
  6. Clarke TSO, Zaidi AM, Clarke B. Leadless pacemakers: practice and promise in congenital heart disease. J Congenit Cardiol. 2017;1:4. 
  7. The LEADLESS Pacemaker IDE Study (Leadless II). ClinicalTrials.gov. Available at http://bit.ly/2oHt5T7. Accessed August 25, 2017.
  8. Leier M. Advancements in pacemaker technology: the leadless device. Crit Care Nurse. 2017;37(2):58-65.
  9. Longitudinal Coverage With Evidence Development Study on Micra Leadless Pacemakers (Micra CED). ClinicalTrials.gov. Available at http://bit.ly/2HWJYST. Accessed August 25, 2017.
  10. Reynolds D, Duray GZ, Omar R, et al. A Leadless Intracardiac Transcatheter Pacing System. N Engl J Med. 2016;374:533-541.
  11. Neale T. Leadless pacing shows promise, but hits snags. MedPage Today. Published May 10, 2014. Available at http://bit.ly/2HY1DcS. Accessed August 25, 2017.
  12. Reddy VY, Knops RE, Sperzel J, et al. Permanent leadless cardiac pacing: Results of the LEADLESS trial. Circulation. 2014;129:1466-1471.
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