News | May 14, 2010

ICD Shock Reduction Programming Strategies Validated

May 14, 2010 – New evidence demonstrates key shock-reduction programming strategies significantly reduced implantable cardioverter-defibrillator (ICD) and cardiac resynchronization therapy defibrillator (CRT-D) shocks from 17 to 28 percent. The study also identified programming and patient characteristics that increased the risk of shocks. These results, from an 89,000-patient study, were released during the late-breaking clinical trials session at Heart Rhythm 2010 yesterday in Denver.

“Improving programming by using evidence-based shock reduction strategies can significantly reduce shocks to patients,” said Bruce Wilkoff, M.D., director of cardiac pacing and tachyarrhythmia devices at the Cleveland Clinic and professor of medicine at The Cleveland Clinic Lerner College of Medicine of Case Western Reserve University in Cleveland. He is also a paid consultant for Medtronic, which conducted the study. “Most importantly, strategies to minimize shocks may further improve survival and quality of life in ICD patients.”

Shock Reduction Programming
The Virtual ICD study data predicted 98 percent of studied implantable defibrillator patients would be free of inappropriate shocks one year after implant and 92 percent at five years post-implant. The study used a statistical model that predicts that six advanced shock-reduction algorithms for ICDs and CRT-Ds can reduce inappropriate shocks experienced by patients.

Results demonstrated how key shock-reduction programming strategies (lengthening the number of intervals to detect ventricular fibrillation [VF NID], using supraventricular tachycardia [SVT] discriminators and employing antitachycardia pacing [ATP]), reduced shocks by 17, 22 and 28 percent, respectively. Additionally, data also demonstrated patients programmed to a slower detection threshold or who had atrial fibrillation with fast ventricular rates were at an increased risk of shocks (up to 148 and 244 percent, respectively).

The findings identify clinical actions and programming solutions to reduce morbidity from shocks. This retrospective analysis used ICD and CRT-D patient data collected through the Medtronic CareLink Network, a remote monitoring service with more than 500,000 cardiac device patients.

“Among implanting physicians, shock reduction is a top priority,” said Kent Volosin, M.D., cardiologist at the University of Pennsylvania in Philadelphia. “This evidence demonstrates that these advanced shock-reduction technologies could help physicians dramatically reduce inappropriate shocks.”

Inappropriate Shocks
Medtronic estimates that more than 70,000 lives have been saved by shocks from implantable defibrillators during the last five years. While the majority of lifesaving shocks are appropriate, studies estimate about 20 percent of patients with implantable defibrillators may experience inappropriate shocks within 2.5 years after implant. The shocks are a response to a nonlethal arrhythmia or electrical noise within the device system.³

Data outlining the need for advanced shock reduction technology to reduce inappropriate shocks will be released Saturday, May 15, at Heart Rhythm 2010. Data on the impact of inappropriate shocks on health care utilization and the adoption rate of device programming strategies aimed at reducing shocks also will be released.

About the Virtual ICD Study
Researchers leading the Virtual ICD study developed a model that was retrospectively applied to 736 arrhythmic and nonarrhythmic shock episodes observed in patients who were enrolled in a multiyear clinical study. The Virtual ICD study modeled the effectiveness of six Medtronic-exclusive algorithms designed to distinguish between life threatening, nonlife threatening arrhythmias or oversensing to reduce the delivery of inappropriate shocks. These algorithms are called SmartShock Technology and are automatically on when the device is implanted. SmartShock Technology is exclusively available on Medtronic Protecta devices now available in Europe. They are investigational only and under review by the U.S. Food and Drug Administration (FDA).

The SmartShock Technology algorithms include:

• Three solutions (Wavelet + PR Logic, SVT discrimination in the VF zone, and Confirmation +) in Protecta devices are designed to discriminate between different nonlethal and lethal arrhythmias to provide lifesaving shock therapy only when necessary.

• T-wave Discrimination and Lead Noise Discrimination features are designed to distinguish between deadly arrhythmias and oversensing to withhold shock therapy when appropriate.

• Lead Integrity Alert, first released in 2008, provides advanced warning of potential lead fractures so the patient can seek medical attention, and reduces the risk of receiving an inappropriate shock.

ICD, CRT Technology
ICDs and CRT-Ds are 98 percent effective in stopping life-threatening fast or irregular heart beats, also known as ventricular arrhythmias, which can lead to sudden cardiac death.¹ Approximately 75 percent of arrhythmias can be terminated with Medtronic’s painless antitachycardia pacing (ATP) technologies and others receive life-saving shock therapy.²

Medtronic has supported eight major shock-reduction clinical trials (Shock-Less, PREPARE, PainFree Rx I and II, PainFree SST, WAVE, ADVANCE III and EMPIRIC).

For more information:


1 DP Zipes, D Roberts, for the Pacemaker-Cardioverter-Defibrillator investigators. "Results of the International Study of the Implantable Pacemaker Cardioverter-Defibrillator: A Comparison of Epicardial and Endocardial Lead Systems." Circulation. 1995;92:59-65.
² Wathen MS, et al. Circulation. 2004;110:2591-2596. Wathen MS, et al. Circulation. 2001;104:796-801.
³ Kadish A, Dyer A, Daubert JP, et al. "Defibrillators in Non-Ischemic Cardiomyopathy Treatment Evaluation (DEFINITE). Prophylactic defibrillator implantation in patients with nonischemic dilated cardiomyopathy.) New England Journals of Medicine. May 20, 2004;350(21):2151-2158.

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