The need for treatment of arrhythmias Overview of Arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more 
depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic drugs Medications for Arrhythmias 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... read more , cardioversion-defibrillation Direct Current (DC) Cardioversion-Defibrillation 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... read more , implantable cardioverter-defibrillators (ICDs), pacemakers Cardiac Pacemakers 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... read more 
(and a special form of pacing, cardiac resynchronization therapy Cardiac Resynchronization Therapy (CRT) 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... read more ), catheter ablation Ablation for Cardiac Arrhythmia 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... read more , surgery Surgery for cardiac arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more , or a combination, is used.
ICDs cardiovert or defibrillate the heart in response to ventricular tachycardia Ventricular Tachycardia (VT) Ventricular tachycardia is ≥ 3 consecutive ventricular beats at a rate ≥ 120 beats/minute. Symptoms depend on duration and vary from none to palpitations to hemodynamic collapse and death. Diagnosis... read more (VT) or ventricular fibrillation Ventricular Fibrillation (VF) Ventricular fibrillation causes uncoordinated quivering of the ventricle with no useful contractions. It causes immediate syncope and death within minutes. Treatment is with cardiopulmonary... read more 
(VF). 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 Cardiac Resynchronization Therapy (CRT) 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... read more 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 Overview of Cardiomyopathies A cardiomyopathy is a primary disorder of the heart muscle. It is distinct from structural cardiac disorders such as coronary artery disease, valvular disorders, and congenital heart disorders... read more , a left ventricular ejection fraction of < 35%, and a high risk of VT or VF. Other indications (see table Indications for Implantable Cardioverter-Defibrillators Indications for Implantable Cardioverter-Defibrillators in Ventricular Tachycardia and Ventricular Fibrillation 
) are less clear .
Because ICDs treat rather than prevent VT or VF, patients prone to these arrhythmias may require both an ICD and antiarrhythmic drugs Medications for Arrhythmias 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... read more to reduce the number of episodes and need for uncomfortable shocks; this approach also prolongs the life of the ICD.
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.
