Practice Essentials

An implantable cardioverter-defibrillator (ICD) is a specialized device designed to directly treat many dysrhythmias, and it is specifically designed to address ventricular tachyarrhythmias. ICDs have revolutionized the treatment of patients at risk for sudden cardiac death due to ventricular tachyarrhythmias. A permanent pacemaker is an implanted device that provides electrical stimuli, thereby causing cardiac contraction when intrinsic myocardial electrical activity is inappropriately slow or absent. See the image below. All modern ICDs also function as pacemakers.

100% ventricular paced rhythm.

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Indications for ICD placement

Indications for ICD implantation can be divided into two broad categories: secondary prophylaxis against sudden cardiac death and primary prophylaxis. For secondary prophylaxis, ICD placement is indicated as initial therapy in survivors of cardiac arrest due to ventricular fibrillation (VF) or hemodynamically unstable ventricular tachycardia (VT). Published guidelines exclude cases in which there are “transient or reversible causes,”^[1]although in the specifics of its application this exclusion is somewhat controversial.

Currently, indications for primary prophylaxis account for most ICD implants. Measurable quantitative benefit is smaller in the primary prophylaxis population than in the secondary prophylaxis population. Class I indications (ie, the benefit greatly outweighs the risk, and the treatment should be administered) are as follows:

Structural heart disease, sustained VT

[Guideline] Epstein AE, DiMarco JP, Ellenbogen KA, et al. 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. J Am Coll Cardiol. 2008 May 27. 51(21):e1-62. [QxMD MEDLINE Link].
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Hobbs JB, Peterson DR, Moss AJ, et al. Risk of aborted cardiac arrest or sudden cardiac death during adolescence in the long-QT syndrome. JAMA. 2006 Sep 13. 296(10):1249-54. [QxMD MEDLINE Link].
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Almendral J, Arribas F, Wolpert C, et al. Dual-chamber defibrillators reduce clinically significant adverse events compared with single-chamber devices: results from the DATAS (Dual chamber and Atrial Tachyarrhythmias Adverse events Study) trial. Europace. 2008 May. 10(5):528-35. [QxMD MEDLINE Link].
Hauser RG, Kallinen LM, Almquist AK, et al. Early failure of a small-diameter high-voltage implantable cardioverter-defibrillator lead. Heart Rhythm. 2007 Jul. 4(7):892-6. [QxMD MEDLINE Link]. [Full Text].
Kallinen LM, Hauser RG, Lee KW, et al. Failure of impedance monitoring to prevent adverse clinical events caused by fracture of a recalled high-voltage implantable cardioverter-defibrillator lead. Heart Rhythm. 2008 Jun. 5(6):775-9. [QxMD MEDLINE Link].
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Morrison TB, Friedman PA, Kallinen LM, et al. Impact of implanted recalled Sprint Fidelis lead on patient mortality. J Am Coll Cardiol. 2011 Jul 12. 58(3):278-83. [QxMD MEDLINE Link]. [Full Text].
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Media Gallery

Third-degree heart block. Image courtesy of James Heilman, MD, via Wikimedia Commons.
Electrocardiogram showing complete heart block. The ventricular rate is 25 per minute, the QRS complex is very wide, and there is atrioventricular dissociation. Image courtesy of Case Reports in Cardiology ((Jafar NS, et al. Rapidly Progressive Atrioventricular Block in a Patient with Sarcoidosis. Case Rep Cardiol. 21 Aug 2014; Article ID 372936).
Complete heart block. Likely a Mobitz II block with sequential blocked P waves.
Intermittent periods of ventricular capture.
100% ventricular paced rhythm.

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Table 1. Indications for ICD Implant

Indication	Classification	Supporting Studies
Structural heart disease, sustained VT	Class I	AVID, CASH, CIDS
Syncope of undetermined origin, inducible VT or VF at EPS	Class I	CIDS
LVEF ≤35% due to prior MI, at least 40 days post-MI, NYHA Class II or III	Class I	SCD-HeFT
LVEF ≤35%, NYHA Class II or III	Class I	SCD-HeFT
LVEF ≤30% due to prior MI, at least 40 days post-MI	Class I	MADIT II
LVEF≤40% due to prior MI, inducible VT or VF at EPS	Class I	MADIT, MUSTT
Unexplained syncope, significant LV dysfunction, nonischemic CM	Class IIa	Expert opinion
Sustained VT, normal or near-normal ventricular function	Class IIa	Expert opinion
Hypertrophic cardiomyopathy (CM) with 1 or more major risk factors	Class IIa	Expert opinion
Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) with 1 or more risk factors for sudden cardiac death (SCD)	Class IIa	Expert opinion
Long QT syndrome, syncope or VT while receiving beta blockers	Class IIa	Zareba et al,^[37] Viskin et al,^[38] Goel et al,^[39] Monnig et al,^[40] Goldenberg et al,^[41] Hobbs et al^[42]
Nonhospitalized patients awaiting heart transplant	Class IIa	Expert opinion
Brugada syndrome, syncope	Class IIa	Expert opinion
Brugada syndrome, VT	Class IIa	Expert opinion
Catecholaminergic polymorphic VT, syncope or VT while receiving beta blockers	Class IIa	Expert opinion
Cardiac sarcoidosis, giant cell myocarditis, or Chagas disease	Class IIa	Expert opinion
CM = cardiomyopathy; EPS = electrophysiologic studies; ICD = implantable cardioverter-defibrillator; LVEF = left ventricular ejection fraction; MI = myocardial infarction; NYHA = New York Heart Association; VF = ventricular fibrillation; VT = ventricular tachycardia.

Table 2. Pacemaker Code Used to Describe Various Pacing Modes

1st Position	2nd Position	3rd Position	4th Position	5th Position
Chamber Paced	Chamber Sensed	Response to Sensing	Rate Modulation	Multisite Pacing
A	A	T	O	O
V	V	I	R	A
D	D	D		V
	O	O		D
A = atrium, D = dual (both chambers), I = inhibited, O = none, R = rate adaptive, T = triggered, V = ventricle.

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#author-disclosures{display:block}#author-disclosures.modal-layer{position:relative}#author-disclosures .modal-content{max-height:none}#author-disclosures .close-modal{display:none}

Author

Daniel M Beyerbach, MD, PhD Medical Director, Cardiac Rhythm Program, The Christ Hospital; Affiliate Clinical Assistant Professor of Biomedical Science, Florida Atlantic University

Daniel M Beyerbach, MD, PhD is a member of the following medical societies: American College of Cardiology

Disclosure: Nothing to disclose.

Chief Editor

Jeffrey N Rottman, MD Professor of Medicine, Department of Medicine, Division of Cardiovascular Medicine, University of Maryland School of Medicine; Cardiologist/Electrophysiologist, University of Maryland Medical System and VA Maryland Health Care System

Jeffrey N Rottman, MD is a member of the following medical societies: American Heart Association, Heart Rhythm Society

Disclosure: Nothing to disclose.

Acknowledgements

Lawrence C Brilliant, MD Clinical Assistant Professor, Department of Primary Care and Community Services, MCP Hahnemann University; Attending Physician, Department of Emergency Medicine, Doylestown Hospital