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November 07, 2012
Study Shows How to Reduce Inappropriate Shocks from Defibrillators
MAYWOOD, Ill. - Loyola University Medical Center is one of the centers participating in a landmark study that could lead to fewer inappropriate shocks from implanted defibrillators.
Implanted defibrillators save lives by shocking hearts back into a normal rhythm. But sometimes a defibrillator can go off when it's not necessary, delivering a shock that feels like a kick in the chest.
The study found reprogramming defibrillators to be less sensitive to irregular heart rhythms reduced the number of inappropriate shocks, while also reducing mortality. The study was presented at a meeting of the American Heart Association Scientific Sessions and is being published in the New England Journal of Medicine.
"Inappropriate shocks can be painful and psychologically traumatic to patients," said cardiologist Dr. Peter Santucci, medical director of Loyola's Implant Device Program. "It's important to reduce these shocks, and results of this study will help us to do this, while also potentially improving patients' survival."
Santucci enrolled Loyola patients in the multicenter international trial. Dr. David Wilber, director of Loyola's Cardiovascular Institute, is a co-author of the paper.
The trial is known as MADIT-RIT (Multicenter Automatic Defibrillator Implantation Trial - Reduce Inappropriate Therapy). First author is Dr. Arthur J. Moss of the University of Rochester Medical Center.
An implantable cardioverter defibrillator (ICD) is about the size of a pocket watch and is implanted below the collarbone. Wire leads connect to the heart. The device is designed to protect against tachyarrhythmias - quivering, superfast heartbeats that prevent the heart from pumping blood effectively.
When the heart goes into a tachyarrhythmia, the ICD's pacemaker is activated. If the pacemaker fails to restore a normal rhythm, the ICD then delivers a powerful electric shock that jolts the heart back into a normal rhythm. But previous research, cited in the new paper, found that ICDs are inappropriately activated in between 8 percent and 40 percent of patients.
Under conventional programming, an ICD may be activated if the heart rate reaches 170 to 199 beats per minute for 2.5 seconds or at least 200 beats per minute for 1 second. If the heart rate does not slow within 5 to 10 seconds, a shock may be delivered.
The study included 1,500 patients who were randomly assigned to three groups. The first group had ICDs with conventional programming. In the second group, the ICDs would not activate unless the heart rate was at least 200 beats per minute. In the third group, the ICDs were programmed to have longer delays before activation (for example, a 60-second delay when the heart rate was at 170 to 199 beats per minute).
After an average follow-up of 1.4 years, patients in the second group had a 79 percent reduction in first-time inappropriate ICD activation. Patients in the third group had a 76 percent reduction in first-time inappropriate activation.
There was a 55 percent reduction in deaths in the second group and a 44 percent reduction in deaths in the third group.
Wilber is a professor and Santucci is an associate professor in the Department of Medicine, Division of Cardiology of Loyola University Chicago Stritch School of Medicine.
Loyola University Health System (LUHS) is a member of Trinity Health. Based in the western suburbs of Chicago, LUHS is a quaternary care system with a 61-acre main medical center campus, the 36-acre Gottlieb Memorial Hospital campus and more than 30 primary and specialty care facilities in Cook, Will and DuPage counties. The medical center campus is conveniently located in Maywood, 13 miles west of the Chicago Loop and 8 miles east of Oak Brook, Ill. The heart of the medical center campus is a 559-licensed-bed hospital that houses a Level 1 Trauma Center, a Burn Center and the Ronald McDonald® Children's Hospital of Loyola University Medical Center. Also on campus are the Cardinal Bernardin Cancer Center, Loyola Outpatient Center, Center for Heart & Vascular Medicine and Loyola Oral Health Center as well as the LUC Stritch School of Medicine, the LUC Marcella Niehoff School of Nursing and the Loyola Center for Fitness. Loyola's Gottlieb campus in Melrose Park includes the 255-licensed-bed community hospital, the Professional Office Building housing 150 private practice clinics, the Adult Day Care, the Gottlieb Center for Fitness, Loyola Center for Metabolic Surgery and Bariatric Care and the Loyola Cancer Care & Research at the Marjorie G. Weinberg Cancer Center at Melrose Park.