Implantable Cardioverter-Defibrillators (ICD)
(See also Overview of 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 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 yr.
ICDs are the preferred treatment for patients who have had
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 in Ventricular Tachycardia and Ventricular Fibrillation).
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
ICDs may malfunction by
ICDs may deliver inappropriate pacing or shocks in response to sinus rhythm, SVTs, 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.
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.