Public access defibrillator use increasing

Public access defibrillator use increasing

ORLANDO, Fla., Nov. 9 – Use of portable defibrillators by non-emergency responders on victims of cardiac arrest doubled during a four-year period in Seattle and King County, Washington. Survival rates were similar to or better than those of people treated by emergency medical service workers, researchers reported at the American Heart Association’s Scientific Sessions 2003.

Public access defibrillation (PAD) is when someone other than a traditional emergency medical worker applies an automated external defibrillator (AED) to treat out-of-hospital cardiac arrest. Cardiac arrest occurs when the heart suddenly stops beating normally and cannot pump blood to the rest of the body, causing death within minutes, unless the patient gets cardiopulmonary resuscitation (CPR). For many victims, an electrical shock to the heart from an AED is their only chance for survival.

“PAD was used in only a small proportion of all treated out-of-hospital arrests, but the proportion increased over time,” said Thomas D. Rea, M.D., M.P.H., an epidemiologist at the Division of Emergency Medical Services, Public Health for Seattle and King County, Wash.

Researchers tracked out-of-hospital cardiac arrests treated by public access defibrillation between January 1, 1999 and December 31, 2002 in Seattle and King County. They wanted to determine how frequently public defibrillators were used.

PAD accounted for 1.3 percent (50 people) of 3,754 cardiac arrests treated during the study period, increasing from 0.82 percent in 1999 to 2.05 percent in 2002.

For those treated with PAD, survival was 50 percent according to hospital discharge data.

“This survival rate is encouraging,” said Rea, though he added that the study was not designed to determine whether PAD improves survival.

Businesses and other entities in the community that bought their own AEDs and trained responders registered with the Seattle area’s voluntary Community Responder AED Program. In all, 457 AEDs were registered, and more than 4,000 people were trained to use them.

“The primary aim of the PAD program was to make sure that, in a cardiac arrest, everything was in place so the victim would have the best chance at survival,” Rea said.

About 250,000 U.S. residents die from sudden cardiac arrest each year, according to the American Heart Association. This is about half of all deaths from coronary heart disease.

Defective Heart Defibrillators Recalled by Guidant Corporation
Defective Heart Defibrillators Recalled by Guidant Corporation 2
• E Defibrillator com Explains the Benefits of Portable Defibrillators
• E Defibrillator com Explains the Function of Defibrillators
• Frequently Asked Questions about the Guidant Recall
• Guidant Defibrillator Patients Urged to Register For Information Updates
• Plano Man Sues Over Flawed Heart Defibrillator
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Anger, exertion can spark irregular beat in patients with implantable defibrillators

Anger, exertion can spark irregular beat in patients with implantable defibrillators

DALLAS, Sept. 10 – People with implantable defibrillators are more likely to experience a life-threatening irregular heart rhythm when they exercise or get angry, according to research published in today’s rapid access issue of Circulation: Journal of the American Heart Association.

Implantable cardioverter-defibrillators (ICDs) are placed in the hearts of people who have had abnormal heart rhythms (arrhythmias), such as rapid heartbeats or quivering of the left ventricle (ventricular fibrillation), which are potentially life-threatening. The devices identify arrhythmias and give an electrical shock to restore normal rhythm. The shock has been likened to a kick in the chest. People who have ventricular fibrillation and don’t receive a shock are at risk for sudden death.

“We were interested in finding what triggers these dangerous rhythms,” says the study’s senior author Diwakar Jain, M.D., professor of cardiovascular medicine and director of nuclear cardiology at the Drexel University College of Medicine in Philadelphia. “We were able to take recordings from the defibrillators, identify when arrhythmias occurred, and correlate that information with reports of mood and physical exertion.”

Observational studies have suggested that psychological stress increases the risk of sudden death in the population at large. Until now, only indirect or anecdotal evidence suggested that anger and vigorous exercise played a role in arrhythmias, according to Jain.

Between 1996 and 1999, 240 patients completed diaries that reflected their mood and physical exertion levels, each on a five-point intensity scale. After receiving an ICD shock, patients recorded the emotions they were feeling shortly before the shock. They served as their own controls by recording their emotions at the same time a week later (the control period).

Forty-two patients (33 men, average age 65) had 107 confirmed ventricular arrhythmias requiring shock. Anger level was rated three or higher in 15 percent of shock events versus 3 percent during control periods. The 15 percent who were shocked at these times were driving, arguing, gambling or had received bad news.

Patients were engaged in physical activity (level 4 or greater) within 15 minutes preceding 53 percent of shocks and during 32 percent of control periods. The exertion included walking slowly or vigorously, recreational activity or physical activity at work.

The study suggests that anger management techniques and ways to block responses to physical stressors may help avoid arrhythmia incidents, says Jain.

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defective defibrillator claim Southern California

MADIT II Trial -- Prophylactic Implantation of a Defibrillator in Patients with Myocardial Infarction and Reduced Ejection Fraction

MADIT II Trial -- Prophylactic Implantation of a Defibrillator in Patients with Myocardial Infarction and Reduced Ejection Fraction

Brian McGovern, M.D.
Massachusetts General Hospital; Chairman, Atrial Fibrillation Foundation

Over the last decades, there has been great progress in reducing death from cardiovascular causes, but there is much to be done. Cardiovascular disease is still the single most common cause of death in the United States. Patients with myocardial infarction (MI) and reduced left ventricular function are at the highest risk for congestive heart failure (CHF) and arrhythmia-related sudden cardiac death (SCD). Statistics show that there are 340,000 out-of-hospital or emergency room cardiac arrests per year in the United States — 50 percent in absence of acute MI. There is a 95 percent out-of-hospital mortality for these patients. This extremely low survival rate has motivated the prophylactic implantation of a defibrillator for primary prevention.

For treatment of patients at risk for SCD due to ventricular tachyarrhythmias, the implantable cardioverter/defibrillator (ICD) has revolutionized treatment. Advances in technology have improved ICDs, making them easier to implant and safer for patients. They are smaller, much more complex and have improved battery life from the days of their inception in 1980 and approval by the Food and Drug Administration (FDA) in 1985.

The second Multicenter Automatic Defibrillator Implantation Trial (MADIT II) was conducted to help better identify patients with coronary heart disease who would benefit from an ICD. MADIT II is the latest in a series of trials involving the use of ICDs to improve management and clinical treatment of arrhythmia patients. The Antiarrhythmics versus Implantable Defibrillators (AVID) Trial compared ICDs with antiarrhythmic-drug therapy (amiodarone or sotalol, predominantly the former) in patients who had survived life-threatening ventricular arrhythmias. Once it was established that defibrillator therapy had a clear advantage over drug therapy, the trial was stopped. (1)

Previous trials examined the role of the ICD as primary therapy in patients who have never experienced symptomatic arrhythmias but have risk markers for sudden death. The first Multicenter Automatic Defibrillator Implantation Trial (MADIT) and the Multicenter Unsustained Tachycardia Trial (MUSTT) showed that patients with coronary heart disease, a reduced left ventricular ejection fraction, unsustained ventricular tachycardia and inducible sustained ventricular tachyarrhythmias in the electrophysiology lab benefited from ICD implantation. (2) Read brief reviews of all trials.

The Coronary Artery Bypass Graft (CABG) Patch Trial evaluated the prophylactic use of ICDs in patients undergoing coronary revascularization surgery. A high risk of death due to arrhythmia was considered to be indicated by a noninvasive marker — an abnormal signal-averaged electrocardiogram — plus an ejection fraction below 36 percent. (3) The CABG Patch Trial showed no benefit to ICD therapy.

In MADIT II patients with a prior MI and a left ventricular ejection fraction of 0.30 or less were randomly assigned in a 3:2 ratio to receive an ICD (742 patients) or conventional medical therapy (490 patients), with all-cause mortality as the primary end point. Electrophysiologic testing or inducible ventricular arrhythmias were not eligibility criteria for MADIT II. The findings revealed that in patients with a previous MI and reduced left ventricular ejection fraction, the prophylactic use of an ICD, in addition to medications, significantly reduced the risk of death.

Results from MADIT II have been widely anticipated because the trial was well designed with excellent follow-up. Other strong features of the trial included:

• Low rate of crossover
• High frequency of adjunctive medications in both groups
• Primary endpoint of all-cause mortality
• Timing of mortality benefit
• CHF admissions and other long-term risks

During 20 months of follow-up of the study group, there was a 31 percent reduction in the relative risk of mortality among patients in the ICD group compared with those in the conventional therapy group. Because of the reduced risk of mortality seen in the trial, the Data Safety and Monitoring Board stopped the trial early (November 2001). The results are especially significant because ICD therapy was “on top of optimal medical management.” Use of beta-blockers in both treatment arms, for example, was 70 percent, and use of statins was 67 percent in the ICD group and 64 percent in the conventional therapy group.

ICD therapy was associated with the expected rates of device-related complications, but, more importantly, was also associated with a higher rate of new or worsened heart failure than was conventional therapy. While this was a troublesome finding, the research team speculated that effective treatment of potential lethal arrhythmias leads to longer survival, thus allowing heart failure to develop. It is possible that other explanations, such as adverse effects of chronic pacing, may have contributed to this observation.

In general, the conclusion of MADIT II is:

• In patients with reduced EF and history of MI, ICD implantation confers a mortality benefit.
• There is a concerning trend toward an increase in CHF admissions in the ICD group.
• Cost considerations are substantial, but will require an assessment of full survival benefit.
• Subgroup analysis, in particular, assessment of EPS in risk stratification, may be helpful in transitioning these results into clinical practice.

Despite the significant economic implications of this study, MADIT II has proven that the potential patient population that could benefit from prophylactic treatment is large — an estimated 3 to 4 million patients have coronary heart disease and advanced left ventricular dysfunction in the United States, with an estimated 340,000 new cases annually. All healthcare professionals who have patients in this population should be aware of the findings and encourage the use of this method when a patient’s profile warrants consideration of implantation. Additional studies to identify subgroups at higher or lower risk than the overall population would be very helpful. The accompanying PowerPoint presentation (see link under Related Items near the top of this Web page) covers the results derived from previous trials — AVID, MUSTT, MADIT and CABG Patch — and further defines the MADIT II trial and findings.

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cardiac defibrillator

Internal Cardioverter Defibrillator (ICD) and Antiarrhythmic Drug Interaction

Internal Cardioverter Defibrillator (ICD) and Antiarrhythmic Drug Interaction

Steven Singh, M.D.

ICDs were developed and have been most frequently used for prevention of sudden cardiac death in patients with life-threatening ventricular arrhythmias such as sustained VT or VF. Epidemiological studies report high rates of recurrence of these life-threatening arrhythmias (30% to 50% in 2 years) during follow-up. Early observational reports documenting efficacy in reversion of sustained VT and VF have now been supplemented by large prospective and sometimes randomized single-center and multicenter studies with long-term outcome data. Enrollment in these trials has included patients with coronary and noncoronary heart diseases with a wide range of ventricular function and coexisting disorders.

These studies uniformly document sudden cardiac death recurrence rates that average 1% to 2% annually after device implantation in these populations. Simultaneously, rapid technological evolution of ICD systems has occurred. The ICD has evolved from a short-lived nonprogrammable device requiring a thoracotomy for lead insertion into a multiprogrammable antiarrhythmia device inserted almost exclusively without thoracotomy, now capable of treating bradycardia, VT, and VF. Clinical studies have recorded major improvements in implant risk, system longevity, symptoms associated with arrhythmia recurrences, quality of life and diagnosis and management of inappropriate device therapy. Implantation, follow-up and replacement of these devices is a complex process requiring familiarity with device capabilities, adequate case volume, continuing education and skill in the management of ventricular arrhythmias, therefore mandating involvement of a trained electrophysiologist to provide an optimal personnel team for patient safety and device management. A substantial new body of information has emerged regarding the clinical outcome of patients with VT or VF treated with currently available antiarrhythmic therapies. There are currently three major therapeutic options to reduce or prevent VT or VF in patients at risk for these arrhythmias. These are:

1. Antiarrhythmic drug therapy selected by electrophysiological study or ambulatory monitoring or prescribed empirically.
2. Ablative techniques applied at cardiac surgery or percutaneously using catheter techniques.
3. Implantation of a cardioverter-defibrillator device system.

A combination of ICD therapy with drugs or ablation is also frequently used. Currently the largest clinical experience is with combined antiarrhythmic drug and ICD therapy. The role of antiarrhythmic drugs combined with an ICD has not been thoroughly evaluated, though several clinical trials have been conducted. The results of these studies raise a number of important clinical issues in patients with life-threatening ventricular arrhythmias. Antiarrhythmic therapy, with the possible exception of sotalol, should be prescribed selectively in patients with ICDs, given their potential for cardiac and noncardiac toxicity.

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Defibrillation

Defibrillation

Defibrillation is a process in which an electronic device, called an automated external defibrillator (AED), helps reestablish normal contraction rhythms in a heart that's not beating properly. It does this by delivering an electric shock to the heart. All emergency personnel should be trained and allowed to use a properly maintained defibrillator if their job requires them to respond to people having cardiac arrest. This includes all first-responding emergency personnel, both hospital and non-hospital.

It's essential to integrate early defibrillation into an effective emergency cardiac care system. This means employing the "chain of survival" concept. The components of this concept are:

• Early access to the emergency medical services system (call 9-1-1 immediately)
• Early CPR (cardiopulmonary resuscitation) when needed
• Early defibrillation when indicated
• Early advanced cardiac care

To make early defibrillation possible, it's essential that a defibrillator be immediately available to emergency personnel responding to a cardiac arrest. Thus, all emergency ambulances and other emergency vehicles that respond to or transport heart patients should be equipped with a defibrillator.

What can I do to help improve access to AEDs in my community?

• Find out if the first-responder vehicles (ambulances, police cars and fire department vehicles) in your community are equipped with AEDs. If they are not, ask why.
• Speak to members of city councils, county boards and state legislatures. Advocate starting an early defibrillation program in your community, including equipping all first responders with AEDs.
• Support allocating funds to establish an early defibrillation program and to equip all first responders with AEDs in your community.
• Advocate and support regulatory changes in your state that expand the use of AEDs by a broader range of first responders.

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Response to Food and Drug Administration clearance of automated external defibrillator for home use

Response to Food and Drug Administration clearance of automated external defibrillator for home use: "Response to Food and Drug Administration clearance of automated external defibrillator for home use

November 13, 2002

The Food and Drug Administration recently gave clearance for an automated external defibrillator (AED) designed for use in the home. AEDs are portable medical devices that provide the most effective treatment for sudden cardiac arrest victims who have a deadly abnormal heart rhythm known as ventricular fibrillation.

Sudden cardiac arrest is responsible for approximately 340,000 adult deaths per year in the U.S. Approximately 95 percent of those who suffer sudden cardiac arrest outside a hospital die. For many people, sudden cardiac arrest is the first sign of cardiovascular disease.

More than 70 percent of all out-of-hospital sudden cardiac arrests occur in the home. Therefore, it has been suggested that family members of individuals at risk of sudden cardiac arrest should be trained and equipped to provide CPR and attempt defibrillation. The American Heart Association recommends early defibrillation as a potentially life-saving treatment and recognizes there are different approaches to making early defibrillation possible. Data from lay rescuer defibrillation programs in public locations have shown that the highest survival from sudden cardiac arrest occurs when the arrest is witnessed an and when bystanders provide immediate CPR and defibrillation within three to five minutes of the arrest.

Prior to making a formal recommendation about home defibrillation, the American Heart Association needs more data on the overall effectiveness of this approach. Data is limited on the number of times a cardiac arrest in the home is witnessed and who is most at risk. Questions also exist about the level of training necessary to make successful resuscitation likely. The American Heart Association looks forward to reviewing the results of an ongoing scientific trial, funded by the National Heart, Lung, and Blood Institute, which will provide valuable data about the home use of AEDs in a few years.

At this time, in the absence of scientific evidence of effectiveness, the American Heart Association can not recommend broad adoption of the home use of AEDs. The association does encourage anyone with questions about their risk factors for heart disease to discuss their treatment options with their physicians. Families of those at risk should learn to identify the signs of sudden cardiac arrest and call 9-1-1 immediately if any of the signs occur. In addition, the American Heart Association recommends that family members learn CPR so they’re prepared to help a loved one survive sudden cardiac arrest.

The American Heart Association is working to improve survival from sudden cardiac arrest by strengthening the chain of survival in every community. The chain of survival includes rapid recognition of a cardiac emergency, early access to emergency medical services (EMS) system by calling 9-1-1, effective bystander CPR, early defibrillation and early access to advanced care.

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New drug reduces abnormal heart rhythms in patients with implanted cardioverter defibrillators

New drug reduces abnormal heart rhythms in patients with implanted cardioverter defibrillators: "New drug reduces abnormal heart rhythms in patients with implanted cardioverter defibrillators

This is featured simultaneously in a news conference at Scientific Sessions 2004 and published in the rapid access issue of Circulation: Journal of the American Heart Association (7:30 a.m. CST, Monday, Nov. 8, 2004).

NEW ORLEANS, Nov. 8 – A new drug reduced the recurrence of abnormal heart rhythms in patients with a defibrillator implanted in their heart, researchers reported today in a late-breaking clinical trial session at the American Heart Association’s Scientific Sessions 2004.

Results were simultaneously published in Circulation: Journal of the American Heart Association.

An implantable cardioverter defibrillator (ICD) is a device that treats life-threatening abnormal heart rhythms by delivering an electrical shock to the heart. Defibrillators can treat the abnormal rhythms when they happen, but many patients need other treatment to prevent symptomatic arrhythmias and to reduce the number of device therapies, explained Paul Dorian, M.D., M.Sc., director of the arrhythmia service, St. Michael’s Hospital, Toronto and professor of medicine, University of Toronto, Toronto, Canada; and chair of the SHock Inhibition Evaluation with AzimiLiDe (SHIELD) steering committee.

ICDs can deliver a shock to restore a normal rhythm or provide anti-tachycardia pacing (ATP), a series of pacing pulses to steady the rhythm. The machine records each patient’s arrhythmic episodes, and physicians can download that data by placing a probe on the patient’s skin.

The investigational drug, azimilide dihydrocholoride, blocks potassium channel currents in the heart known as I_KS and I_KR that can cause abnormal heart rhythms. The drug is known as a class III anti-arrhythmic agent.

In this study, 633 ICD recipients from 121 sites in nine countries were randomized to one of three groups: one 75 milligram (mg) daily dose of the azimilide dihydrocholoride, one 125 mg daily dose of the drug, or a placebo. Participants included patients with newly implanted ICDs who had experienced a life-threatening arrhythmia during the 42 days prior to implantation and patients who had their ICDs for more than 30 days and had a documented episode of arrhythmia in the 180 days before receiving the device.

The researchers found that azimilide dihydrocholoride reduced the total number of all-cause shocks plus the number of times ATP was used to steady ventricular tachycardia (VT). A ventricular tachyarrhythmia is a condition in which the defibrillator correctly treats the arrhythmia but the patient can experience recurrences with symptoms that may include shortness of breath, chest pain, dizziness or fainting. Relative risk reductions were 57 percent with the 75 mg dose and 47 percent with the 125 mg dose (relative to those taking a placebo).

In addition, the incidence of all appropriate ICD therapies (shocks or pacing-terminated VT) was reduced 48 percent among patients on 75 mg of azimilide dihydrocholoride, and 62 percent in patients taking 125 mg. Five patients in the test group and one in the placebo group developed torsade de pointes, a rhythm disturbance. All were successfully treated with the ICD. One patient in the 75 mg group developed severe but reversible neutropenia, a diminished number of neutrophils (a type of white blood cells) in the blood.

Co-authors are: Martin Borggrefe, M.D.; Hussein R. Al-Khalidi, Ph.D.; Stefan H. Hohnloser, M.D.; Jose M. Brum, M.D.; Daljit S. Tatla, Ph.D.; Johannese Brachmann, M.D.; Robert J. Myerburg, M.D.; David S. Cannon, M.D.; Michael van der Laan, M.d.; Michael J. Holroyde, Ph.D.; Igor Singer, M.D.; Craig M. Pratt, M.D. Disclosure information is included in the journal article.

Statements and conclusions of study authors that are published in the American Heart Association scientific journals are solely those of the study authors and do not necessarily reflect association policy or position. The American Heart Association makes no representation or warranty as to their accuracy or reliability.

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Implantable defibrillators cost-effective for preventing sudden death

Implantable defibrillators cost-effective for preventing sudden death: "Implantable defibrillators cost-effective for preventing sudden death

DALLAS, April 16 - In the first study of its kind, an implantable cardioverter defibrillator (ICD), a device used to treat heart rhythm abnormalities, was found to be moderately cost-effective for preventing sudden cardiac death, according to a report in today's rapid access Circulation: Journal of the American Heart Association.

ICDs deliver electrical shocks to the heart to eliminate abnormal rhythms such as ventricular fibrillation or ventricular tachycardia. In the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial, the device was shown to be superior to therapy with antiarrhythmic medications for reducing all causes of death in survivors of ventricular fibrillation (irregular, chaotic heart rhythm that begins in the heart's lower chambers). It was also a better choice for people with ventricular tachycardia (an often serious rapid rhythm originating in the lower chambers) and ejection fractions of 40 percent or less. Ejection fraction is a measure of the heart's pumping ability.

AVID is the first study to prospectively determine the cost-effectiveness of ICDs for secondary prevention in the United States, according to lead author Greg Larsen, M.D, a staff cardiologist at the Portland VA Medical Center and associate professor of medicine at the Oregon Health and Sc"

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Arrhythmia

Arrhythmia: "Arrhythmias are disorders of the regular rhythmic beating of the heart. They're common — as many as 2.2 million Americans are living with atrial fibrillation (one type of rhythm problem). Arrhythmias can occur in a healthy heart and be of minimal consequence. They also may indicate a serious problem and lead to heart disease, stroke or sudden cardiac death. The goal of this site is to help the public and healthcare professionals learn more about arrhythmias, and ultimately reduce disability and death from heart disease and stroke. Do your part by learning the facts and taking the steps needed to understand and control arrhythmias."

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Preventing sudden death with implantable defibrillators

Preventing sudden death with implantable defibrillators: "Preventing sudden death with implantable defibrillators"

In the current issue of the New England Journal of Medicine (March 21), researchers report results from a study in which individuals who had a prior heart attack received an implantable defibrillator to keep their hearts from stopping suddenly, causing sudden death. Implantable defibrillators are devices used in people who have fast heartbeats, conditions called recurrent or sustained ventricular tachycardia or fibrillation. Leads positioned inside the heart sense cardiac rhythm and deliver electric shocks to pace the heart as needed.

Results were released early today at the American College of Cardiology meeting in Atlanta by Arthur Moss, M.D., of the University of Rochester in New York, during the Late-Breaking Clinical Trials session.

The devices are used to prevent sudden death in patients with ventricular fibrillation, but this is the first large study that has tested the devices in individuals who do not have such abnormal rhythms, and who are at high risk for sudden death because their hearts are damaged from prior heart attacks.

The study, called MADIT-II (Multicenter Automatic Defibrillator Implantation Trial), included 1,232 patients who had suffered a heart attack and had an ejection fraction of 30 percent or less. Ejection fraction is a measure of how much blood is pumped from the heart chamber. Normal ejection fraction is between 50 and 75 percent.

Patients were randomly assigned to either receive the implantable defibrillator or treatment with conventional medical therapy. There was a 31 percent reduction in the risk of death in the defibrillator group compared with the conventional-therapy group.

On the downside, more patients treated with the defibrillator suffered worsening heart failure - 19.9 percent compared to 14.9 percent - for the medically-treated group.

According to David Faxon, M.D., president of the American Heart Association, "This study answers some important questions about whether implantable devices are better than medical therapy in preventing sudden death, which accounts for about one half of all deaths from coronary heart disease. The reduction seen in this study is substantial.

"Should patients with these characteristics - prior heart attack and ejection fraction less than 30 - be treated with an implantable defibrillator? It's too soon to make sweeping recommendations without considering the increased costs and complications from heart failure associated with defibrillators.

"The next step is to narrow in on the type of patient who would benefit most, maximizing the benefits, while keeping costs low."

It should also be stressed that the "high tech" approach in treating patients may not be needed if more individuals focused on "low tech" methods to prevent coronary artery disease, such as getting plenty of exercise, not smoking and watching one's diet.

It's also important for individuals to get to the hospital as soon as they have signs of heart attack, because we may be able to limit the amount of heart damage, thus averting the need for a defibrillator, says Faxon.

American Heart Association

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Implantable Cardioverter Defibrillator

Implantable Cardioverter Defibrillator

An implantable cardioverter defibrillator is used in patients at risk for recurrent, sustained ventricular tachycardia or fibrillation.

The device is connected to leads positioned inside the heart or on its surface. These leads are used to deliver electrical shocks, sense the cardiac rhythm and sometimes pace the heart, as needed. The various leads are tunnelled to a pulse generator, which is implanted in a pouch beneath the skin of the chest or abdomen. These generators are typically a little larger than a wallet and have electronics that automatically monitor and treat heart rhythms recognized as abnormal. Newer devices are smaller and have simpler lead systems. They can be installed through blood vessels, eliminating the need for open chest surgery.

When an implantable cardioverter defibrillator detects ventricular tachycardia or fibrillation, it shocks the heart to restore the normal rhythm. New devices also provide overdrive pacing to electrically convert a sustained ventricular tachycardia, and "backup" pacing if bradycardia occurs. They also offer a host of other sophisticated functions (such as storage of detected arrhythmic events and the ability to do "noninvasive" electrophysiologic testing).

Implantable cardioverter defibrillators have been very useful in preventing sudden death in patients with known, sustained ventricular tachycardia or fibrillation. Studies are now being done to find out how best to use them and whether they may have a role in preventing cardiac arrest in high-risk patients who haven't had, but are at risk for, life-threatening ventricular arrhythmias.

According to the American Heart Association Heart and Stroke Statistical Update, in 1998 (the most recent statistics available) there were 26,000 ICD procedures.

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