Taking the Lead

Author: 
Shana Leonard

Several pacemaker and implantable cardioverter defibrillator (ICD) manufacturers are taking the seriousness of lead fractures to heart. As a result, some next-generation cardiac rhythm-management (CRM) devices could feature ‘leadless’ designs.

Leads have historically carried out a critical function in devices. In ICDs, for instance, leads are typically attached transvenously to the heart on one end and to a pulse generator at the other end. They deliver electrical stimuli from the generator to the heart in order to restore a life-threatening abnormal heart rhythm to normal.

But as is the case with most implants, there are risks, including perforation of the heart during implantation and possible lead fracture. The latter issue has been subjected to heightened scrutiny in the wake of a 2007 Medtronic Inc. recall of its Sprint Fidelis transvenous defibrillator leads; their potential for fracture has been implicated in 13 deaths.  

Although the benefits of transvenous leads appear to outweigh the risks, it can’t hurt to explore design options that promote safer products and procedures. That’s what a few pioneering companies are doing with ‘leadless’ devices, which do not directly interface with the heart through transvenous wires.

While the term ‘leadless’ has been used to describe these unconventional devices, it is not always an accurate label, notes Thomas Osypka, president and CEO of Oscor Inc., a specialist in implantable lead fabrication. “Even though the system is called leadless, there is still a highly reliable conductor connected between the generator and cardiac muscle that very much looks and functions like a lead,” he says. “The way the electrode system is implanted is completely different compared to what we are used to seeing. However, the electrical connection stays and looks the same.”

Falling into this category is a subcutaneous ICD developed by Cameron Health Inc. for the treatment of sudden cardiac arrest. Consisting of a parasternal electrode and a left lateral thoracic pulse generator, the S-ICD system provides life-saving shocks while eliminating direct contact between wires and the heart. Studies published in the July issue of the New England Journal of Medicine reported that the S-ICD detected ventricular fibrillation in 100% of 137 induced episodes.

Critics, however, have condemned the system’s higher energy requirements, compared with traditional ICDs, as well as the resulting larger form factor. The S-ICD is also not suitable for use in patients that require a pacing system as well; it may provide effective treatment in only 25% of current defibrillator patients, according to a May New York Times article. Yet despite these limitations, the ‘leadless’ system presents an interesting option for that 25% of patients for whom the S-ICD is optimized.

In the pacemaker space, Medtronic is also leaving leads behind, although it has remained tight-lipped about the details. “Medtronic is developing a leadless pacemaker that would be delivered to the heart by a catheter. We would expect to begin human implants in the next three to five years,” says Medtronic spokesperson Christopher Garland. “While we cannot predict the future of the market, we do believe that a leadless pacemaker could achieve market acceptance.”

With Medtronic leading the leadless charge, others may follow in due time. Could a new era of CRM device design be on the horizon?