The implantable cardioverter-defibrillator (ICD) has dramatically changed the treatment of patients who are at risk for sudden cardiac death (SCD) as a result of ventricular tachyarrhythmias. The device has evolved from a therapy of last resort to first-line treatment and prophylactic therapy for patients at risk for ventricular tachycardia (VT) and/or ventricular fibrillation (VF).
GUIDELINES FOR USE
The American College of Cardiology (ACC) and the American Heart Association (AHA), along with the American Association for Thoracic Surgery and the Society of Thoracic Surgeons, have set evidence-based guidelines for the use of ICDs. Indications for ICD implantation can be divided into two categories: primary prophylaxis and secondary prophylaxis against SCD. The greatest predictors of risk for SCD are left ventricular systolic function and heart failure symptoms.1
Most ICDs are implanted for primary prophylaxis. The ACC/AHA classifies these indications as either class I or class IIa. Class I means the treatment is useful, the benefit greatly outweighs the risk, and the treatment should be administered. Class IIa means that the benefit outweighs the risk and the treatment should be administered1 (Table: Indications and classifications for implantable cardioverter-defibrillators in the online version of this article).
The indications for secondary prophylaxis against SCD are well-supported by multiple clinical trials. Studies have shown that the ICD is superior to an tiarrhythmic drugs in patients with a history of VT or VF who are at risk for SCD. ICD implantation is recommended as initial therapy in all survivors of cardiac arrest caused by VF or hemodynamically unstable VT.1,2
TECHNOLOGIC ADVANCES
ICDs can perform one or all of the following functions: antitachycardia pacing, cardioversion, defibrillation, and/or bradycardia pacing. The devices are programmed to detect cardiac arrhythmias and to correct them by delivering a jolt of electricity. ICDs can distinguish between atrial and ventricular arrhythmias and are equipped to perform biventricular pacing in patients with heart failure or bradycardia. Newer-model ICDs can distinguish between VT and VF; in the case of VT, the device will try to pace the heart at a rate faster than its intrinsic rate in order to break the tachycardia before it progresses to VF. ICDs use multiple methods to determine if a fast rhythm is normal, VT, or VF. Additionally, ICDs are capable of distinguishing the regularity of a rhythm, and because VT is usually regular whereas atrial fibrillation (AF) is typically irregular, ICDs will not send out a shock if a patient has AF. The devices can also compare the morphology of every ventricular beat with what the ICD believes is a normally conducted ventricular impulse for the individual patient.
One risk of ICD therapy has been inappropriate shocks. Newer models have greatly reduced this risk.
The subcutaneous ICD can deliver enough energy to defibrillate the heart without having a lead in or on the heart. The unit is positioned just under the skin and outside the rib cage. Implantation is considered a minor procedure and is done under conscious sedation.3
POSTIMPLANTATION CARE
Follow-up care is essential, and whenever possible, patients should be referred to a dedicated ICD clinic. Education is important. Recipients must avoid strong electromagnetic fields, such as MRI magnets, shock wave lithotripsy, and/or electrocauterization. Common household appliances, microwave ovens, and cell phones do not pose any serious threat. Patients need to understand that an ICD shock is painful. Driving may pose problems; the general recommendation is that patients be shock-free for 6 months before they resume driving. Many patients with ICDs may still require adjunctive therapy, such as pharmacologic agents and/or radiofrequency catheter ablation. JAAPA
Mary Hewett is Assistant Professor, Division of Physician Assistant Studies, Medical University of South Carolina, Charleston, and the department editor for When the Patient Asks. She has indicated no relationships to disclose relating to the content of this article.
REFERENCES
1. 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;51(21):e1-e62.
2. Levy WC, Lee KL, Hellkamp AS, et al. Maximizing survival benefit with primary prevention implantable cardioverter-defibrillator therapy in a heart failure population. Circulation. 2009;120(10):835-842.
3. Implantable cardioverter defibrillator. Cleveland Clinic Web site. http://my.clevelandclinic.org/heart/services/tests/ procedures/icd.aspx. Accessed April 6, 2010.
Click NEXT for Patient Information.