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Protection Against Sudden Cardiac Death With the Implantable Defibrillator
Protection Against Sudden Cardiac Death With the Implantable Defibrillator
Several hundred thousand patients every year die in the United States from sudden cardiac death. The usual cause is a rapid heart beat originating from the pumping chambers, and most patients have pre-existing heart disease.
When a person experiences a cardiac arrest, there are only a few minutes to interrupt the process, prevent irreversible brain damage, and save a life. Bystander CPR is critical, as is prompt defibrillation with an external defibrillator, either delivered by an automatic external defibrillator (AED) or by skilled medical personnel. Unfortunately, about 95% of patients who experience a cardiac arrest do not survive. In urban areas, the mortality rate may be as high as 98%.
In order to prevent the fatal cardiac arrest, it is useful to predict which patients are most likely to experience this deadly event and protect them in advance. Protection takes the form of an implantable cardioverter defibrillator (ICD) installed to serve as a safeguard against the possibility of a life-threatening rapid heart beat. Should this occur, the implanted device will detect and terminate the arrhythmia within seconds, thus preventing death and pre-emptying the need to have a successful resuscitative effort.
This concept of "prophylactic ICD placement" or "primary prevention of sudden death" has been tested in several clinical trials over the last several years. Patients were selected for these clinical trials based on a perceived increased likelihood of experiencing cardiac arrest and sudden death. The hypothesis tested was simple, i.e. that an ICD placed in appropriate high-risk individuals will reduce the overall death rate. Several important clinical trials were performed, completed and published and have largely clarified which patients will benefit from primary placement of an ICD. These trials included MADIT-I and II, SCD-HeFT, DEFNITE, and COMPANION. In aggregate, these large scale clinical investigations have established that patients who have severe cardiac dysfunction, because of either a prior heart attack or other damage to their heart muscle, will benefit from an ICD.
Patients with heart conditions should have a specific measurement of their heart function called an "ejection fraction". This is the key defining characteristic of long-term prognosis, and also benefit from the ICD. In general, patients with an ejection fraction below 35% may benefit from the ICD with other qualifying characteristics depending on the nature of the heart condition and the patient's clinical state. Some patients require other tests to help elucidate need for the ICD.
In aggregate, the overall death rate can be reduced at approximately 25-50% depending on underlying risk. This is a substantial mortality reduction and will have a direct impact on sudden death rates in the United States.
All patients with heart conditions should be evaluated with appropriate tests by their physicians to determine need for ICD. Consultation with an electrophysiologist is often also required. It should be emphasized, that primary prevention ICD placement does not require a prior life-threatening arrhythmia; the entire concept is based on protection against the first potentially fatal event.
ICD placement is a relatively simple surgical procedure performed under local anesthesia at minimal risk, often in an ambulatory setting (see Implantable Device Section).
