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First-of-its-Kind ICD Aims to Prevent Sudden Cardiac Death Without Connecting to the Heart


Northwestern Medicine is one of only 46 sites worldwide to participate in the pivotal study of Medtronic’s Extravascular Implantable Cardioverter Defibrillator

Joseph Mulligan Portrait

CHICAGO -  After his second cardiac event in five years, Joseph Mulligan was not surprised when his Northwestern Medicine cardiologist, James Flaherty MD, recommended an implantable cardioverter defibrillator (ICD) as a safeguard to help keep him alive if he were to have a sudden cardiac arrest. At 84 years old, the resident of South Bend, Ind., knew many people with pacemakers and expected, like his friends, he would need a traditional transvenous defibrillator implant with thin wires (leads) threaded directly into his heart and veins to deliver electric therapy to his heart if needed.

Then his medical team presented him with a unique option – Mulligan was a candidate for a clinical trial to test the safety and efficacy of a first-of-its-kind extravascular implantable cardioverter defibrillator (EV ICD). The Medtronic EV ICD is designed to treat dangerously fast heart rhythms that can lead to sudden cardiac arrest, while avoiding certain risks of traditional, transvenous ICDs.

“The EV-ICD involves placement of a special lead that is tunneled under the sternum, so that the lead is not in the heart, but is very close to the outside of the heart,” says Bradley P. Knight, MD, medical director of electrophysiology at Bluhm Cardiovascular Institute. “This allows for lower energy and smaller battery requirements to defibrillate the heart in the event of a cardiac arrest and for pacing of the heart to treat slow heart rates or to terminate fast ventricular tachycardias.”

Northwestern Medicine Bluhm Cardiovascular Institute was the only site in Chicago and one of only 46 sites worldwide to participate in a pivotal study of the device. The results of the trial were presented at the European Society of Cardiology (ESC) Congress 2022 in Barcelona and published in The New England Journal of Medicine.

Worldwide, hundreds of thousands of ICDs are implanted in patients every year to treat dangerously fast heart rhythms. With traditional transvenous defibrillators, the lead is inserted through a vein and attached to the heart leaving the lead under constant stress from the heart beating and movement of the upper body, potentially causing breakage of the lead or blockage of the vein. A totally subcutaneous defibrillator is currently available as an alternative to a transvenous defibrillator, but the device is very large and is unable to pace the heart. The goal of the EV ICD system is to provide the benefits of current transvenous ICDs, but with a smaller device, greater device longevity and without placing leads in the heart or vasculature.

“By positioning the leads outside of the heart, there is less risk of long-term complications associated with leads in the heart and veins, such as the narrowing, blockage or compression of a vein and risks for blood infection,” says Dr. Knight, a co-author on the study.

The EV ICD Pivotal study enrolled 356 patients in 17 countries across North America, Europe, the Middle East, Asia, Australia and New Zealand. Participants in the trial, like Mr. Mulligan, received the same therapies provided by traditional ICDs, including defibrillation, anti-tachycardia pacing and back-up pacing therapies, with this single implanted device.

The trial met its primary objectives: defibrillation therapy effectiveness at implant was 98.7%. This reflects a greater defibrillation efficacy for the EV ICD than historical transvenous ICD studies, and comparable efficacy to the subcutaneous ICD despite EV ICD’s smaller device size. The study also exceeded its safety endpoint: at six months, 92.6% of patients were free from major system and/or procedure-related major complications such as hospitalization, system revision, or death.

“The EV-ICD is a revolution in implantable defibrillator technology that addresses the limitations of our existing therapies that have been available for several decades,” says Dr. Knight. “With the promising data from this trial, we have an opportunity to evolve ICD technology in a safe, effective manner and improve this lifesaving therapy.”

For Mulligan, now 86 years old, the option to enroll in the clinical trial is one he is thankful for as he continues to lead a very active life with the EV ICD as a safety net.

“I feel terrific and I’m grateful to have the advantage of having this device, which I know is keeping me alive longer than I should be,” says Mulligan, an alum of Notre Dame who remains active with the university as president of class of ’59 and a member of the Notre Dame community choir. “The whole process was very easy – I was only hospitalized overnight, and my scar has already almost completely disappeared.”

Worldwide, the EV ICD system is investigational and not yet approved for sale or distribution. Medtronic has received FDA approval for a Continue Access Study, and patients in the pivotal study will continue to be followed until Medtronic receives regulatory approval for the EV ICD system in the United States. The clinical trial was funded by Medtronic; number, NCT04060680

To learn more about cardiovascular clinical trials at Northwestern Medicine, visit the Bluhm Cardiovascular Institute – Clinical Trial Unit.

Bluhm Cardiovascular Institute is an innovative powerhouse in developing the latest, safest advances in cardiovascular care. Anchored in downtown Chicago, it has expanded and integrated into eight Northwestern Medicine hospitals, most recently bringing advanced cardiovascular services to the south suburbs at Northwestern Medicine Palos Hospital. Consistently recognized as one of the top cardiology and cardiac surgery programs in the country, Bluhm Cardiovascular Institute at Northwestern Memorial Hospital is ranked eighth in the country by U.S. News & World Report in the annual “America’s Best Hospitals” rankings. For more information, visit