Implantable cardioverter-defibrillators (ICDs) are small battery-powered devices that can deliver a small electric shock to the heart in response to a life-threatening arrhythmia (when the heart starts beating rapidly and inefficiently).

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According to Dr. Sana Al-Khatib, lead researcher of the study published Tuesday in the Journal of the American Medical Association, ICDs often are recommended as a primary prevention tactic for patients who are at high risk for a cardiac arrest or life-threatening arrhythmia, but who have not yet suffered from these symptoms.

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