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Implantable Cardioverter-Defibrillators (ICD)


L. Brent Mitchell

, MD, Libin Cardiovascular Institute of Alberta, University of Calgary

Last full review/revision Jan 2021| Content last modified Jan 2021

The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic drugs, cardioversion-defibrillation, implantable cardioverter-defibrillators (ICDs), pacemakers (and a special form of pacing, cardiac resynchronization therapy), catheter ablation, surgery, or a combination, is used.

ICDs cardiovert or defibrillate the heart in response to ventricular tachycardia (VT) or ventricular fibrillation (VF). Contemporary tiered-therapy ICDs also provide antibradycardia pacing and antitachycardia pacing (to terminate responsive atrial or ventricular tachycardias) and store intracardiac electrograms.

ICDs are implanted subcutaneously or subpectorally, with electrodes inserted transvenously into the right ventricle and sometimes also the right atrium. A biventricular ICD also has a left ventricular epicardial lead placed via the coronary sinus venous system or via thoracotomy to allow cardiac resynchronization therapy pacing (CRT-D). ICD platforms also include an ICD that is completely implanted subcutaneously (S-ICD) with no intravascular components, and a wearable vest-like defibrillator for short-term use.

Impulse generators for ICDs typically last about 5 to 7 years.

Indications for ICDs

ICDs are the preferred treatment for patients who have had

  • An episode of VF or hemodynamically significant VT not due to reversible or transient conditions (eg, electrolyte disturbance, antiarrhythmic drug proarrhythmia, acute myocardial infarction)

ICDs may also be indicated for patients with VT or VF inducible during an electrophysiologic study and for patients with idiopathic or ischemic cardiomyopathy, a left ventricular ejection fraction of < 35%, and a high risk of VT or VF. Other indications are less clear (see table Indications for Implantable Cardioverter-Defibrillators).

Because ICDs treat rather than prevent VT or VF, patients prone to these arrhythmias may require both an ICD and antiarrhythmic drugs to reduce the number of episodes and need for uncomfortable shocks; this approach also prolongs the life of the ICD.

Indications for Implantable Cardioverter-Defibrillators in Ventricular Tachycardia and Ventricular Fibrillation

Level of Evidence

Specific Indications

Indicated (established by evidence)

Hemodynamically unstable VT or VF when there is no transient or reversible cause

Hemodynamically stable sustained VT in patients with a structural heart disorder

Syncope of undetermined origin with hemodynamically significant sustained VT or VF induced during an electrophysiologic study

Ischemic cardiomyopathy, NYHA class II or III heart failure symptoms during optimal medical therapy, and LV ejection fraction ≤ 0.35 measured at least 40 days post-MI

Ischemic cardiomyopathy, NYHA class I heart failure symptoms during optimal medical therapy, and LV ejection fraction ≤ 30% measured at least 40 days post-MI

Nonischemic dilated cardiomyopathy, NYHA class II or III heart failure symptoms during optimal medical therapy, and LV ejection fraction ≤ 0.35

Ischemic cardiomyopathy, nonsustained VT, LV ejection fraction ≤ 40% measured at least 40 days post-MI, and inducible VF or sustained VT detected during an electrophysiologic study

Possibly indicated and supported by bulk of evidence

Patients with idiopathic dilated cardiomyopathy, significant LV dysfunction during optimal medical therapy, with unexplained syncope

Patients with sustained VT and normal or near-normal ventricular function

Patients with HCM with one or more high risk factors other than sustained VT/VF (family history of premature sudden death, unexplained syncope, LV thickness ≥ 30 mm, abnormal exercise BP response, nonsustained VT)

Patients with ARVC with one or more high risk factors other than sustained VT/VF (extensive RV disease, affected family member with sudden death, undiagnosed syncope, nonsustained VT, inducible VT detected during an electrophysiologic study)

Long QT syndrome, syncope or VT while receiving a beta-blocker

Nonhospitalized patients awaiting cardiac transplantation

Brugada syndrome and syncope or documented VT that has not resulted in cardiac arrest

Patients with catecholaminergic polymorphic VT with syncope and/or documented sustained VT while receiving a beta-blocker

Patients with cardiac sarcoidosis, giant cell myocarditis, or Chagas disease

Possibly indicated but less well supported by evidence

Patients with idiopathic dilated cardiomyopathy, NYHA class I heart failure symptoms during optimal medical therapy, LV ejection fraction ≤ 0.35

Patients with long QT syndrome, without syncope or VT and with one or more high risk factors (QTc > 0.5 second, LQT1 with 2 abnormal copies of the abnormal gene and deafness [formerly Jervell and Lange-Neilsen syndrome], LQT2, LQT3)

Patients with syncope and an advanced structural heart disorder if invasive and noninvasive investigations have not identified a cause

Patients with familial cardiomyopathy associated with sudden death

Patients with LV noncompaction

Not indicated

Syncope of unknown etiology in absence of inducible VT or VF and without a structural heart disorder

Incessant VT or VF

VT or VF with mechanisms amenable to catheter or surgical ablation

VT or VF due to transient or reversible disorders when correction is feasible and likely to prevent recurrence

Psychiatric disorders that may worsen with ICD implantation or that preclude follow-up

Patients with no reasonable expectation of survival and with an acceptable functional status for ≥ 1 year

Patients with NYHA class IV drug-refractory heart failure symptoms who are not candidates for cardiac transplantation or a CRT ICD

ARVC = arrhythmogenic right ventricular cardiomyopathy; BP = blood pressure; CRT = cardiac resynchronization therapy; HCM = hypertrophic cardiomyopathy; ICD = implantable cardioverter defibrillator; LQT1 = long QT syndrome type 1; LQT2 = long QT syndrome type 2; LQT3 = long QT syndrome type 3; LV = left ventricular; MI = myocardial infarction; NYHA = New York Heart Association; QTc = corrected QT interval; RV = right ventricular; VF = ventricular fibrillation; VT = ventricular tachycardia.

Adapted from Epstein AE, DiMarco JP, Ellenbogen KA, et al: 2012 ACCF/AHA/HRS focused update incorporated into the ACCF/AHA/HRS 2008 Guidelines for device-based therapy of cardiac rhythm abnormalities. Circulation 127(3):e283–e352, 2013.

ICD malfunction

ICDs may malfunction by

  • Delivering inappropriate pacing or shocks
  • Not delivering pacing or shocks when needed

ICDs may deliver inappropriate pacing or shocks in response to sinus rhythm, supraventricular tachycardia, atrial fibrillation, atrial flutter, or nonphysiologically generated impulses (eg. due to lead fracture).

ICDs may not deliver appropriate pacing or shocks when needed because of factors such as lead or impulse generator migration, undersensing, an increase in pacing threshold due to fibrosis at the site of prior shocks, and battery depletion.

When an ICD discharges

In patients who report that the ICD has discharged but that no associated symptoms of syncope, dyspnea, chest pain, or persistent palpitations occurred, follow up with the ICD clinic and/or the electrophysiologist within the week is appropriate. The ICD can then be electronically interrogated to determine the reason for discharge. If such associated symptoms were present, or the patient received multiple shocks, emergency department referral is indicated to look for a treatable cause (eg, coronary ischemia, electrolyte abnormality) or device malfunction.

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