atrial tachyarrhythmias, and these features have been incorporated in some contemporary ICD systems. Cardioversion/defibrillation A shock that is synchronized to be delivered at the peak of the R wave is referred to as cardioversion. Because VT is an organized electrical rhythm, the delivery of an electrical shock during the vulnerable period of repolarization can cause VT to degenerate into ventricular fibrillation (VF). Synchronized cardioversion prevents shock delivery during the vulnerable period. Although ICDs can be programmed to deliver synchronized shocks at a range of energies up to the maximum output of the device (usually 30 to 40 joules), synchronized cardioversion can often terminate VT with relatively low energy (eg, 10 joules or less). (See "Implantable cardioverter-defibrillators: Optimal programming", section on 'Cardioversion'.) An unsynchronized shock (ie, a shock delivered randomly during the cardiac cycle) is referred to as defibrillation. Clinicians can program ICDs to deliver unsynchronized shocks for very rapid ventricular arrhythmias (eg, heart rate greater than 200 beats/min). Because VF is not an organized rhythm, synchronized cardioversion is neither possible nor necessary. Similarly, it can be difficult to synchronize with very rapid VTs, and such rapid rhythms are unlikely to be hemodynamically tolerated. ICDs are typically programmed to deliver synchronized shocks at energies approaching the maximum output of the device (usually 30 to 40 joules) ( waveform 2). (See "Implantable cardioverter-defibrillators: Optimal programming", section on 'Defibrillation'.) Bradycardia pacing All contemporary transvenous ICDs are capable of pacing; however, current S-ICDs can deliver pacing for only 30 seconds post shock delivery and not standard bradycardia pacing. Many patients with an ICD have a conventional indication for cardiac pacing [27]. Separate ICDs and pacemakers can lead to device-to-device interactions, particularly with older models, potentially resulting in inappropriate shocks and underdetection of VT/VF [28-31]. With rare exceptions, patients should have only one transvenous or epicardial device, although the combined use of a leadless pacemaker with an S-ICD is under investigation. Generally, however, when a patient with a pacemaker develops an indication for ICD implantation, the pacemaker is removed and replaced with an ICD. https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 12/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate For patients with known atrioventricular (AV) block or sinus node dysfunction, or those who are receiving left ventricular (LV) pacing as part of cardiac resynchronization therapy (CRT), the device will be programmed accordingly. (See "Modes of cardiac pacing: Nomenclature and selection", section on 'Pacing modes'.) For those without pre-existing AV block or sinus node dysfunction and who presumably do not require regular ventricular pacing, the ICD will typically be programmed to minimize the amount of pacing provided (eg, pace only for intrinsic rates less than 40 beats/min). (See "Overview of pacemakers in heart failure" and "Modes of cardiac pacing: Nomenclature and selection", section on 'Modes to minimize ventricular pacing'.) In addition to the usual indications for pacing, the ability to provide pacing also protects against bradyarrhythmias that can follow a tachycardia or shock, and also against ventricular arrhythmias that are bradycardia-dependent [32]. Because of the unique physiology following a ventricular tachyarrhythmia and device shock, ICDs allow for distinct post-shock pacing programming (usually at higher outputs). S-ICDs are able to provide this brief pacing function. Cardiac resynchronization therapy CRT, which utilizes biventricular pacing, is an effective treatment for symptomatic heart failure in some patients with LV dyssynchrony. CRT is currently recommended in patients with advanced heart failure (usually NYHA class III or IV), severe systolic dysfunction (LV ejection fraction 35 percent), and intraventricular conduction delay (QRS >120 milliseconds). The evidence of benefit is greatest in patients with left bundle branch block and a QRS duration >150 milliseconds. Pacing of the LV is most frequently achieved by transvenous insertion of an electrode into a cardiac vein via the coronary sinus. Surgical placement of an epicardial lead is also an option in patients following failed efforts at transvenous lead placement, or in patients undergoing cardiac surgery for another reason. Conduction system pacing is another means of synchronizing ventricular stimulation; its impact, compared with traditional CRT with an coronary sinus lead, is being actively investigated. (See "Cardiac resynchronization therapy in heart failure: Indications and choice of system" and "Cardiac resynchronization therapy in heart failure: System implantation and programming" and "Cardiac resynchronization therapy in heart failure: Indications and choice of system", section on 'Rationale for CRT'.) Improvement in heart failure can reduce the frequency of ventricular arrhythmias, raising the possibility that biventricular pacing may have an adjunctive role with an ICD by reducing the need for ICD therapy. Although an initial series of 32 patients found such an effect [33], this benefit was not confirmed in the much larger MIRACLE ICD trial of 369 patients [34]. Although the addition of biventricular pacing to ICD therapy was associated with significant improvements https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 13/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate in symptoms and quality of life, there was no reduction in the number of appropriate or inappropriate shocks. (See "Cardiac resynchronization therapy in heart failure: Indications and choice of system" and "Cardiac resynchronization therapy in heart failure: Indications and choice of system", section on 'Rationale for CRT'.) Perioperative ICD functioning During surgical procedures, the function of ICDs may be affected by electromagnetic interference (EMI), most commonly due to use of an electrosurgery unit (ESU). ICDs with integrated bipolar sensing configuration may be more susceptible to EMI than those with true bipolar sensing. Very rarely, direct damage from cautery to the ICD may alter its ability to deliver pacing or shocks or reset the ICD to an alternate or backup mode. The much more common concern is that the device might misinterpret the cautery as tachyarrhythmia, leading to withholding of bradycardia pacing and perhaps inappropriate ICD shocks. A full discussion regarding the perioperative management of patients with an ICD, including optimal monitoring and cardiac implantable electronic device programming, is presented separately. (See "Perioperative management of patients with a pacemaker or implantable cardioverter-defibrillator".) NONVASCULAR CARDIOVERTER-DEFIBRILLATOR Transvenous ICDs have a number of short- and long-term complications that may potentially be avoided with nonvascular systems. (See "Cardiac implantable electronic devices: Periprocedural complications", section on 'Transvenous lead systems' and "Cardiac implantable electronic devices: Long-term complications".) Wearable cardioverter-defibrillator Some patients who are at risk for sudden cardiac death do not meet established criteria for implantation of an ICD or may require only short-term protection (such as patients awaiting subsequent ICD insertion or cardiac transplantation). In such settings, a wearable cardioverter-defibrillator (WCD) may be preferable to either ICD insertion or bystander resuscitation. The indications for use, efficacy, and limitations of the WCD are discussed separately. (See "Wearable cardioverter-defibrillator".) Subcutaneous ICD Some patients who are at risk for sudden cardiac death and require an ICD will have compelling reasons for avoiding the indwelling transvenous leads associated with a standard ICD (eg, other indwelling leads or catheters, high risk for systemic infection, relatively young age at implant with numerous device implants anticipated over a lifetime, high risk for lead fracture, etc). An entirely subcutaneous ICD (S-ICD) can provide an effective alternative means of defibrillation. The S-ICD is discussed separately. (See "Subcutaneous implantable cardioverter defibrillators".) https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 14/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Extravascular ICD The extravascular ICD is not yet approved for use in the United States but if found to be safe and efficacious may provide benefits of antitachycardia pacing that are lacking in S-ICDs. The extravascular ICD has a single lead implanted substernally, and in addition to defibrillation it can deliver pause-prevention and antitachycardia pacing. A preliminary single- arm study in 316 selected patients with indications for an ICD suggests the extravascular ICD can be successfully implanted (in 94.6 percent) and can detect and terminate ventricular arrythmia (98.7 percent) at the time of implantation; there was a moderate but comparable rate of major complications up to six months post-implantation (7.3 percent) with lead dislodgement and wound infection necessitating system removal being the most common [35]. SUMMARY AND RECOMMENDATIONS Indications Because of its high success rate in terminating ventricular tachycardia (VT) and ventricular fibrillation (VF) rapidly, along with the results of multiple clinical trials showing improvement in survival, implantable cardioverter-defibrillator (ICD) implantation is generally considered the first-line treatment option for the secondary prevention of sudden cardiac death (SCD) and for primary prevention in certain populations at high risk of SCD due to VT/VF. However, there are some situations in which ICD therapy is not recommended, including but not limited to patients with VT/VF from a completely reversible disorder and patients without a reasonable expectation of survival with an acceptable functional status for at least one year. (See 'Introduction' above and 'Indications' above and 'ICD not recommended' above.) Components of the ICD The ICD system is comprised of pacing/sensing electrodes, defibrillation electrodes, and a pulse generator ( picture 1). Contemporary ICDs use leads with pace-sense electrodes and shock coils on a single ventricular lead. Most current ICD systems utilize one, two, or three transvenous leads placed via the axillary, subclavian, or cephalic vein, with attachment to a pulse generator in the subcutaneous tissue in the infraclavicular anterior chest wall. Subcutaneous ICD (S-ICD) systems are an effective alternative that avoid indwelling transvenous lead(s) but lack some of the standard capabilities of a traditional transvenous ICD. (See 'Elements of the ICD' above.) Defibrillation threshold (DFT) While DFT used to be very common, in contemporary EP practice, it is infrequently performed due to the results of randomized trials and the performance of contemporary ICD systems. However, DFT testing is generally performed at the time of device implantation in patients receiving an S-ICD and is reasonable in patients undergoing a right pectoral ICD implantation or ICD pulse generator replacement or those with multiple high-risk features for an elevated DFT (ie, patient with high body mass index https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 15/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate on amiodarone with a nonischemic cardiomyopathy). However, DFT testing is commonly omitted in patients undergoing a left pectoral transvenous ICD implantation with a right ventricular apical lead that is functioning appropriately. (See 'Defibrillation threshold testing' above.) ICD functions Contemporary ICDs have extensive storage and monitoring capacities, the ability to deliver antitachycardia pacing (ie, overdrive pacing) to terminate VT, the ability to deliver synchronized and unsynchronized shocks for VT/VF, and the option of bradycardia pacing. (See 'ICD functions' above.) Nonvascular cardioverter defibrillators Transvenous ICDs have a number of short- and long-term complications that may potentially be avoided with nonvascular systems (including wearable cardioverter-defibrillators, subcutaneous, and extravascular ICDs). (See 'Nonvascular cardioverter-defibrillator' above.) The optimal approach to programming of modern ICDs is discussed in detail separately. (See "Implantable cardioverter-defibrillators: Optimal programming".) ACKNOWLEDGMENT The UpToDate editorial staff acknowledges Leonard Ganz, MD, FHRS, FACC, who contributed to an earlier version of this topic review. Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Russo AM, Stainback RF, Bailey SR, et al. ACCF/HRS/AHA/ASE/HFSA/SCAI/SCCT/SCMR 2013 appropriate use criteria for implantable cardioverter-defibrillators and cardiac resynchronization therapy: a report of the American College of Cardiology Foundation appropriate use criteria task force, Heart Rhythm Society, American Heart Association, American Society of Echocardiography, Heart Failure Society of America, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, and Society for Cardiovascular Magnetic Resonance. J Am Coll Cardiol 2013; 61:1318. 2. Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death: A Report of the American College of Cardiology/American Heart Association https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 16/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol 2018; 72:e91. 3. DiMarco JP. Implantable cardioverter-defibrillators. N Engl J Med 2003; 349:1836. 4. Fenelon G, Huvelle E, Brugada P. Initial clinical experience with a new small sized third- generation implantable cardioverter defibrillator: results of a multicenter study. European Ventak Mini Investigator Group. Pacing Clin Electrophysiol 1997; 20:2967. 5. Thijssen J, Borleffs CJ, van Rees JB, et al. Implantable cardioverter-defibrillator longevity under clinical circumstances: an analysis according to device type, generation, and manufacturer. Heart Rhythm 2012; 9:513. 6. Boriani G, Merino J, Wright DJ, et al. Battery longevity of implantable cardioverter- defibrillators and cardiac resynchronization therapy defibrillators: technical, clinical and economic aspects. An expert review paper from EHRA. Europace 2018; 20:1882. 7. Zanon F, Martignani C, Ammendola E, et al. Device Longevity in a Contemporary Cohort of ICD/CRT-D Patients Undergoing Device Replacement. J Cardiovasc Electrophysiol 2016; 27:840. 8. Flaker GC, Tummala R, Wilson J. Comparison of right- and left-sided pectoral implantation parameters with the Jewel active can cardiodefibrillator. The World Wide Jewel Investigators. Pacing Clin Electrophysiol 1998; 21:447. 9. Gold MR, Shih HT, Herre J, et al. Comparison of defibrillation efficacy and survival associated with right versus left pectoral placement for implantable defibrillators. Am J Cardiol 2007; 100:243. 10. Israel CW, Gr nefeld G, Iscolo N, et al. Discrimination between ventricular and supraventricular tachycardia by dual chamber cardioverter defibrillators: importance of the atrial sensing function. Pacing Clin Electrophysiol 2001; 24:183. 11. Wilkoff BL, Fauchier L, Stiles MK, et al. 2015 HRS/EHRA/APHRS/SOLAECE expert consensus statement on optimal implantable cardioverter-defibrillator programming and testing. Heart Rhythm 2016; 13:e50. 12. Strickberger SA, Klein GJ. Is defibrillation testing required for defibrillator implantation? J Am Coll Cardiol 2004; 44:88. 13. Day JD, Doshi RN, Belott P, et al. Inductionless or limited shock testing is possible in most patients with implantable cardioverter- defibrillators/cardiac resynchronization therapy defibrillators: results of the multicenter ASSURE Study (Arrhythmia Single Shock Defibrillation Threshold Testing Versus Upper Limit of Vulnerability: Risk Reduction Evaluation With Implantable Cardioverter-Defibrillator Implantations). Circulation 2007; 115:2382. https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 17/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate 14. Healey JS, Gula LJ, Birnie DH, et al. A randomized-controlled pilot study comparing ICD implantation with and without intraoperative defibrillation testing in patients with heart failure and severe left ventricular dysfunction: a substudy of the RAFT trial. J Cardiovasc Electrophysiol 2012; 23:1313. 15. Guenther M, Rauwolf T, Br ggemann B, et al. Pre-hospital discharge testing after implantable cardioverter defibrillator implantation: a measure of safety or out of date? A retrospective analysis of 975 patients. Europace 2012; 14:217. 16. Brignole M, Occhetta E, Bongiorni MG, et al. Clinical evaluation of defibrillation testing in an unselected population of 2,120 consecutive patients undergoing first implantable cardioverter-defibrillator implant. J Am Coll Cardiol 2012; 60:981. 17. Arnson Y, Suleiman M, Glikson M, et al. Role of defibrillation threshold testing during implantable cardioverter-defibrillator placement: data from the Israeli ICD Registry. Heart Rhythm 2014; 11:814. 18. Phan K, Kabunga P, Kilborn MJ, Sy RW. Defibrillator Threshold Testing at Generator Replacement: Is it Time to Abandon the Practice? Pacing Clin Electrophysiol 2015; 38:777. 19. Kopp DE, Blakeman BP, Kall JG, et al. Predictors of defibrillation energy requirements with nonepicardial lead systems. Pacing Clin Electrophysiol 1995; 18:253. 20. Larsen JM, Heath FP, Riahi S, et al. Single and dual coil shock efficacy and predictors of shock failure in patients with modern implantable cardioverter defibrillators-a single-center paired randomized study. J Interv Card Electrophysiol 2019; 54:65. 21. Sunderland N, Kaura A, Murgatroyd F, et al. Outcomes with single-coil versus dual-coil implantable cardioverter defibrillators: a meta-analysis. Europace 2018; 20:e21. 22. Healey JS, Hohnloser SH, Glikson M, et al. Cardioverter defibrillator implantation without induction of ventricular fibrillation: a single-blind, non-inferiority, randomised controlled trial (SIMPLE). Lancet 2015; 385:785. 23. B nsch D, Bonnemeier H, Brandt J, et al. Intra-operative defibrillation testing and clinical shock efficacy in patients with implantable cardioverter-defibrillators: the NORDIC ICD randomized clinical trial. Eur Heart J 2015; 36:2500. 24. Phan K, Ha H, Kabunga P, et al. Systematic Review of Defibrillation Threshold Testing at De Novo Implantation. Circ Arrhythm Electrophysiol 2016; 9:e003357. 25. Forleo GB, Gasperetti A, Breitenstein A, et al. Subcutaneous implantable cardioverter- defibrillator and defibrillation testing: A propensity-matched pilot study. Heart Rhythm 2021; 18:2072. https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 18/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate 26. Bianchi V, Bisignani G, Migliore F, et al. Safety of Omitting Defibrillation Efficacy Testing With Subcutaneous Defibrillators: A Propensity-Matched Case-Control Study. Circ Arrhythm Electrophysiol 2021; 14:e010381. 27. Best PJ, Hayes DL, Stanton MS. The potential usage of dual chamber pacing in patients with implantable cardioverter defibrillators. Pacing Clin Electrophysiol 1999; 22:79. 28. Calkins H, Brinker J, Veltri EP, et al. Clinical interactions between pacemakers and automatic implantable cardioverter-defibrillators. J Am Coll Cardiol 1990; 16:666. 29. Ellenbogen KA, Edel T, Moore S, et al. A prospective randomized-controlled trial of ventricular fibrillation detection time in a DDDR ventricular defibrillator. Ventak AV II DR Study Investigators. Pacing Clin Electrophysiol 2000; 23:1268. 30. Glikson M, Trusty JM, Grice SK, et al. A stepwise testing protocol for modern implantable cardioverter-defibrillator systems to prevent pacemaker-implantable cardioverter- defibrillator interactions. Am J Cardiol 1999; 83:360. 31. Mattke S, Markewitz A, M ller D, et al. The combined transvenous implantation of cardioverter defibrillators and permanent pacemakers. Pacing Clin Electrophysiol 1997; 20:2775. 32. Fisher JD, Teichman SL, Ferrick A, et al. Antiarrhythmic effects of VVI pacing at physiologic rates: a crossover controlled evaluation. Pacing Clin Electrophysiol 1987; 10:822. 33. Higgins SL, Yong P, Sheck D, et al. Biventricular pacing diminishes the need for implantable cardioverter defibrillator therapy. Ventak CHF Investigators. J Am Coll Cardiol 2000; 36:824. 34. Young JB, Abraham WT, Smith AL, et al. Combined cardiac resynchronization and implantable cardioversion defibrillation in advanced chronic heart failure: the MIRACLE ICD Trial. JAMA 2003; 289:2685. 35. Friedman P, Murgatroyd F, Boersma LVA, et al. Efficacy and Safety of an Extravascular Implantable Cardioverter-Defibrillator. N Engl J Med 2022; 387:1292. Topic 921 Version 53.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 19/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate GRAPHICS NYHA and other classifications of cardiovascular disability Canadian NYHA functional [1] Cardiovascular Specific activity Class [3] classification Society functional scale [2] classification I Patients with cardiac Ordinary physical Patients can perform to disease but without activity, such as completion any activity requiring 7 metabolic equivalents (ie, can resulting limitations of physical activity. walking and climbing stairs, does not cause Ordinary physical angina. Angina with carry 24 lb up 8 steps; activity does not cause undue fatigue, palpitation, dyspnea, or anginal pain. strenuous or rapid prolonged exertion at work or recreation. do outdoor work [shovel snow, spade soil]; do recreational activities [skiing, basketball, squash, handball, jog/walk 5 mph]). II Patients with cardiac disease resulting in slight limitation of physical activity. They are comfortable at rest. Slight limitation of ordinary activity. Walking or climbing stairs rapidly, walking uphill, walking or stair- Patients can perform to completion any activity requiring 5 metabolic equivalents (eg, have sexual intercourse Ordinary physical activity results in fatigue, palpitation, dyspnea, or anginal pain. climbing after meals, in cold, in wind, or when under emotional stress, or only during the few hours after without stopping, garden, rake, weed, roller skate, dance foxtrot, walk at 4 mph on level ground) but awakening. Walking more than 2 blocks on cannot and do not perform to completion activities requiring 7 metabolic equivalents. the level and climbing more than 1 flight of ordinary stairs at a normal pace and in normal conditions. III Patients with cardiac Marked limitation of Patients can perform to disease resulting in marked limitation of ordinary physical activity. Walking 1 to 2 completion any activity requiring 2 metabolic equivalents (eg, shower physical activity. They blocks on the level and are comfortable at rest. Less-than-ordinary climbing 1 flight in normal conditions. without stopping, strip and make bed, clean https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 20/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate physical activity causes windows, walk 2.5 fatigue, palpitation, mph, bowl, play golf, dyspnea, or anginal pain. dress without stopping) but cannot and do not perform to completion any activities requiring >5 metabolic equivalents. IV Patients with cardiac disease resulting in Inability to carry on any physical activity Patients cannot or do not perform to inability to carry on any physical activity without discomfort. Anginal syndrome may completion activities requiring >2 metabolic without discomfort. Symptoms of cardiac be present at rest. equivalents. Cannot carry out activities insufficiency or of the listed above (specific anginal syndrome may be present even at rest. If any physical activity activity scale III). is undertaken, discomfort is increased. NYHA: New York Heart Association. References: 1. The Criteria Committee of the New York Heart Association. Nomenclature and Criteria for Diagnosis of Diseases of the th Heart and Great Vessels, 9 ed, Little, Brown & Co, Boston 1994. p.253. 2. Campeau L. Grading of angina pectoris. Circulation 1976 54:522. 3. Goldman L, Hashimoto B, Cook EF, Loscalzo A. Comparative reproducibility and validity of systems for assessing cardiovascular functional class: Advantages of a new speci c activity scale. Circulation 1981; 64:1227. Graphic 52683 Version 19.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 21/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Examples of transvenous ICD pulse generators Examples of implantable cardioverter-defibrillator pulse generators commonly used in practice in 2015. ICD: implantable cardioverter-defibrillator. Graphic 104721 Version 2.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 22/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Transvenous ICD shock lead configurations With the active can electrode, current flows between the coil(s) right ventricular (RV) electrode and the housing (active can) of the pulse generator. For transvenous leads with two coils, current also flows between two transvenous coils (RV and superior vena cava). ICD: implantable cardioverter-defibrillator. Graphic 113994 Version 1.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 23/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Subcutaneous ICD pulse generator Example of subcutaneous implantable cardioverter-defibrillator pulse generator commonly used in practice in 2015. ICD: implantable cardioverter-defibrillator. Graphic 104722 Version 3.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 24/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Subcutaneous implantable cardioverter-defibrillator Modi ed from: 1. Al-Khatib SM, Friedman P, Ellenbogen KA. De brillators: Selecting the Right Device for the Right Patient. Circulation 2016; 134:1390. 2. Mayo Clinic. Subcutaneous implantable cardioverter-de brillator (S-ICD). https://www.mayoclinic.org/diseases-conditions/ventricular-tachycardia/multimedia/img- 20303862 (Accessed on March 31, 2021). Graphic 130973 Version 1.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 25/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Lateral view of a patient with a subcutaneous implantable cardioverter-defibrillator (S-ICD) Lateral view of a patient with an S-ICD. S-ICD: subcutaneous implantable cardioverter-defibrillator. Reproduced with permission from: Magnusson P, Pergolizzi JV, LeQuang JA. The Subcutaneous Implantable Cardioverter-De brillator. In: Cardiac Pacing and Monitoring, Min M (Ed), IntechOpen, 2019. Copyright Peter Magnusson, MD, PhD. Graphic 131058 Version 2.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 26/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Different ICD lead systems Chest radiographs of two different implantable cardioverter-defibrillator (ICD) systems. Left panel shows an ICD epicardial lead system. Epicardial sensing electrodes are located on the left ventricle (arrow) and the three epicardial patch electrodes are located on the right atrium, and the inferior and lateral walls of the left ventricle. Right panel shows a dual coil transvenous ICD lead system with a pulse generator in the pectoral region. Courtesy of Douglas Kopp, MD. Graphic 56923 Version 3.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 27/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Posteroanterior (PA) and lateral chest radiographs of a subcutaneous implantable cardioverter-defibrillator (S-ICD) Posteroanterior (PA) and lateral chest radiographs of a subcutaneous implantable cardioverter-defibrillator (S-ICD) with the defibrillation lead visible adjacent to the sternum and the pulse generator in the axilla. Graphic 97372 Version 2.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 28/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Implantable cardioverter-defibrillator (ICD) electrogram anti-tachycardia pacin monomorphic ventricular tachycardia (VT) https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 29/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Stored intracardiac electrogram from an ICD showing the development of monomorphic ventricular tachycar which is successfully terminated by a burst of anti-tachycardia pacing delivered by the ICD. This tachycardia i monomorphic VT, but is labeled VF by the device because it was detected in the VF zone due to the rapid rate RA: right atrial; RV: right ventricular; VT: ventricular tachycardia; VF: ventricular fibrillation; ATP: anti-tachycar pacing; AS: atrium sensed; VS: ventricle sensed. Graphic 114829 Version 2.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 30/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Implantable cardioverter-defibrillator (ICD) electrogram shock for ventricular f (VF) Stored intracardiac electrogram from an ICD showing the development of ventricular fibrillation, which is suc terminated by a single shock from the ICD. RA: right atrium; RV: right ventricle; AS: atrium sensed; AP: atrium paced; A pacing: atrial pacing; VF: ventricu fibrillation; PVC: premature ventricular contraction; VPB: ventricular premature beats. Graphic 114831 Version 1.0 https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 31/32 7/6/23, 3:09 PM Implantable cardioverter-defibrillators: Overview of indications, components, and functions - UpToDate Contributor Disclosures Jonathan Piccini, MD, MHS, FACC, FAHA, FHRS Grant/Research/Clinical Trial Support: Abbott [Atrial fibrillation, catheter ablation]; AHA [Atrial fibrillation, cardiovascular disease]; Bayer [Atrial fibrillation]; Boston Scientific [Cardiac mapping, pacemaker/ICD, atrial fibrillation care]; iRhythm [Atrial fibrillation]; NIA [Atrial fibrillation]; Philips [Lead management]. Consultant/Advisory Boards: Abbott [Atrial fibrillation, catheter ablation]; Abbvie [Atrial fibrillation]; Bayer [Atrial fibrillation]; Boston Scientific [Cardiac mapping, atrial fibrillation, pacemaker/ICD]; ElectroPhysiology Frontiers [Atrial fibrillation, catheter ablation]; Element Science [DSMB]; Medtronic [Atrial fibrillation, pacemaker/ICDs]; Milestone [Supraventricular tachycardia]; Pacira [Atrial fibrillation]; Philips [Lead extraction]; ReCor [Cardiac arrhythmias]; Sanofi [Atrial fibrillation]. All of the relevant financial relationships listed have been mitigated. Cara Pellegrini, MD Consultant/Advisory Boards: Abbott [Atrial fibrillation and supraventricular tachycardia]; Biosense Webster [Ablation]; Cook Medical [Lead extraction tools and techniques]. All of the relevant financial relationships listed have been mitigated. N A Mark Estes, III, MD Consultant/Advisory Boards: Boston Scientific [Arrhythmias]; Medtronic [Arrhythmias]. All of the relevant financial relationships listed have been mitigated. Nisha Parikh, MD, MPH No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/implantable-cardioverter-defibrillators-overview-of-indications-components-and-functions/print 32/32