Editing Cardiac arrest (section)

===Secondary prevention===
[[File:Blausen 0543 ImplantableCardioverterDefibrillator.svg|upright=1.3|thumb|Illustration of an [[implantable cardioverter-defibrillator]] (ICD)]]
An [[implantable cardioverter-defibrillator]] (ICD) is a battery-powered device that monitors electrical activity in the heart, and when an arrhythmia is detected, can deliver an electrical shock to terminate the abnormal rhythm. ICDs are used to prevent sudden cardiac death (SCD) in those who have survived a prior episode of sudden cardiac arrest (SCA) due to ventricular fibrillation or ventricular tachycardia.<ref name="Epstein-2008">{{cite journal|display-authors=6|vauthors=Epstein AE, DiMarco JP, Ellenbogen KA, Estes NA, Freedman RA, Gettes LS, Gillinov AM, Gregoratos G, Hammill SC, Hayes DL, Hlatky MA, Newby LK, Page RL, Schoenfeld MH, Silka MJ, Stevenson LW, Sweeney MO, Smith SC, Jacobs AK, Adams CD, Anderson JL, Buller CE, Creager MA, Ettinger SM, Faxon DP, Halperin JL, Hiratzka LF, Hunt SA, Krumholz HM, Kushner FG, Lytle BW, Nishimura RA, Ornato JP, Page RL, Riegel B, Tarkington LG, Yancy CW|date=May 2008|title=ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices): developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons|journal=Circulation|volume=117|issue=21|pages=e350–e408|doi=10.1161/CIRCUALTIONAHA.108.189742|pmid=18483207|doi-access=free}}</ref>

Numerous studies have been conducted on the use of ICDs for the secondary prevention of SCD. These studies have shown improved survival with ICDs compared to the use of anti-arrhythmic drugs.<ref name="Epstein-2008" /> ICD therapy is associated with a 50% [[relative risk reduction]] in death caused by an arrhythmia and a 25% relative risk reduction in all-cause mortality.<ref>{{cite journal|display-authors=6|vauthors=Connolly SJ, Hallstrom AP, Cappato R, Schron EB, Kuck KH, Zipes DP, Greene HL, Boczor S, Domanski M, Follmann D, Gent M, Roberts RS|date=December 2000|title=Meta-analysis of the implantable cardioverter defibrillator secondary prevention trials. AVID, CASH and CIDS studies. Antiarrhythmics vs Implantable Defibrillator study. Cardiac Arrest Study Hamburg . Canadian Implantable Defibrillator Study|journal=European Heart Journal|volume=21|issue=24|pages=2071–2078|doi=10.1053/euhj.2000.2476|pmid=11102258|doi-access=free}}</ref>

Prevention of SCD with ICD therapy for high-risk patient populations has similarly shown improved survival rates in several large studies. The high-risk patient populations in these studies were defined as those with severe [[ischemic cardiomyopathy]] (determined by a reduced [[Ejection fraction|left ventricular ejection fraction]] (LVEF)). The LVEF criteria used in these trials ranged from less than or equal to 30% in MADIT-II to less than or equal to 40% in MUSTT.<ref name="Epstein-2008" /><ref name="Shun-Shin-2017">{{cite journal |vauthors=Shun-Shin MJ, Zheng SL, Cole GD, Howard JP, Whinnett ZI, Francis DP |date=June 2017 |title=Implantable cardioverter defibrillators for primary prevention of death in left ventricular dysfunction with and without ischaemic heart disease: a meta-analysis of 8567 patients in the 11 trials |journal=European Heart Journal |volume=38 |issue=22 |pages=1738–1746 |doi=10.1093/eurheartj/ehx028 |pmc=5461475 |pmid=28329280}}</ref>

Alternatively, a [[wearable cardioverter defibrillator]] (eg, LifeVest) can be used instead of an implantable defibrillator, and the wearable option can be used as a temporary bridge to an implantable device. Such instances are [[endocarditis]] where an implantable device is at high risk of becoming infected if implanted too soon.