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). 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.
© 2017 Elliot K. Fishman, MD.
© 2017 Elliot K. Fishman, MD.
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 (see table Indications for Implantable Cardioverter-Defibrillators) 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 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.
