Traditional implanted pacemakers and defibrillators use thin wires called "leads" to send out electricity that keeps the heart beating properly, but these wires can also be associated with problems, from dislodgements and equipment failures to valve damage and infections.

Medtronic, which already sells a tiny pacemaker without leads, has begun early human testing of a new defibrillator it developed in Minnesota that can deliver high-voltage shocks to restart the heart or re-establish normal rhythm without needing wires that physically touch the heart or blood vessels.

The device "has the potential to deliver the benefits of traditional ICDs while eliminating the risks that can occur when leads are implanted inside the veins and heart," like dislodgements and lead fractures, said Dr. Ian Crozier, the New Zealand doctor who is serving as principal investigator for the clinical trial of the Medtronic device.

Avoiding leads to cut down on complications is not a new concept. Since 2012, Boston Scientific has been selling a device called the Emblem S-ICD, which is a defibrillator that sits just below the skin, usually under the armpit. The Emblem system delivers current to the heart using a lead that also runs just below the skin but above the rib cage, so it doesn't enter blood vessels or the heart.

The MRI-approved Emblem has been a strong growth driver in Boston Scientific's heart division, and CEO Mike Mahoney recently reminded investors that the company has "a multiyear head start" over any competition in the category (Boston Scientific acquired the Emblem's inventor, Cameron Health, in 2012.)

First in-human implant

But Medtronic has been testing and publishing data on what it calls its EV ICD system for years, and last week it announced the first in-human implant for a patient who intends to use the device long-term as part of a clinical study. Medtronic's pilot study will enroll 20 patients at hospitals in Australia and New Zealand and check the patients regularly for safety and device performance.

The Medtronic device is the same size and shape of its traditional ICDs and is being designed to have a similar 10-year battery life. The device is implanted under the skin below the left armpit, and the lead runs underneath the breastbone — instead of above the bone — without entering the heart or blood vessels.

Mike Marinaro, general manager of Medtronic's cardiac rhythm and heart failure division, said in a company announcement, "this pilot study is a significant step forward in our EV ICD clinical development program, as we aim to offer patients the therapies of a traditional transvenous ICD, but without leads implanted in the heart."

("Transvenous" refers to a lead that goes inside a blood vessel, and "EV ICD" is an abbreviation for "Extravascular Implantable Cardioverter Defibrillator." The "S" in S-ICD stands for "subcutaneous," which means under the skin.)

Not the same functions

There are some differences between Boston Scientific's S-ICD and Medtronic's EV ICD.

One of the clearest differences is that the Medtronic device in clinical trials is capable of delivering both high-voltage shocks to restart a heart and low-voltage pacing therapy to treat a slow heart beat. Boston Scientific's device can defibrillate, but it's not suitable for long-term pacing. Medtronic's device can deliver "anti-tachycardia" pacing to stop a racing heart beat, which may avoid the need for defibrillation and preserve battery.

Dr. Ken Stein, chief medical officer for Boston Scientific's heart-rhythm device division, said pacing functions are not being added to future generations of the S-ICD. Instead, the company is designing its new capsule-sized leadless pacemaker called the Empower to communicate with the S-ICD to provide that function in patients who need a defibrillator and pacemaker. The Empower is not currently available for sale anywhere, but it is expected to enter a pivotal U.S. clinical trial next year, Stein said.

There may also be differences in infection risk, voltages need to defibrillate, and battery life, but those remain to be proven out in clinical trials.

Asked when the EV ICD device might be available on the U.S. market, a Medtronic spokeswoman wrote, "Our path to approval will require a pivotal clinical trial. We aren't able to share information about the (FDA approval) timeline, which will be informed by the pilot study as we plan the design, locations, etc., for the pivotal trial."