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Implantable cardioverter-defibrillator

Implantable cardioverter-defibrillator

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An implantable cardioverter-defibrillator (ICD) is a small battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

-powered electrical impulse generator which is implanted in patients who are at risk of sudden cardiac death
Sudden Cardiac Death
Sudden cardiac death is natural death from cardiac causes, heralded by abrupt loss of consciousness within one hour of the onset of acute symptoms. Other forms of sudden death may be noncardiac in origin...

 due to ventricular fibrillation
Ventricular fibrillation
Ventricular fibrillation is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly. Ventricular fibrillation is a medical emergency and most commonly identified arrythmia in cardiac arrest...

 and ventricular tachycardia
Ventricular tachycardia
Ventricular tachycardia is a tachycardia, or fast heart rhythm, that originates in one of the ventricles of the heart...

. The device is programmed to detect cardiac arrhythmia and correct it by delivering a jolt of electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

. In current variants, the ability to revert ventricular fibrillation has been extended to include both atrial and ventricular
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...

 arrhythmias as well as the ability to perform biventricular pacing in patients with congestive heart failure
Congestive heart failure
Heart failure often called congestive heart failure is generally defined as the inability of the heart to supply sufficient blood flow to meet the needs of the body. Heart failure can cause a number of symptoms including shortness of breath, leg swelling, and exercise intolerance. The condition...

 or bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...



The process of implantation of an ICD is similar to implantation of a pacemaker
Artificial pacemaker
A pacemaker is a medical device that uses electrical impulses, delivered by electrodes contacting the heart muscles, to regulate the beating of the heart...

. Similar to pacemakers, these devices typically include electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

 wire(s) which pass through a vein to the right chambers of the heart, usually being lodged in the apex of the right ventricle. The difference is that pacemakers are more often temporary and generally designed to consistently correct bradycardia, while ICDs are often permanent safeguards against sudden abnormalities.

The most recent development is the subcutaneous ICD (S-ICD). Current state-of-the-art electronics and batteries have enabled an implantable device to deliver enough energy to defibrillate the heart without the need for a lead in or on the heart. This prevents lead-related problems and the risk of dangerous infections in or near the heart. This ICD is positioned just under the skin and outside the ribcage. It can be placed during a minor procedure under conscious sedation. A study of 300 patients is in progress for US approvals.

Working mechanism

ICDs constantly monitor the rate and rhythm of the heart and can deliver therapies, by way of an electrical shock, when the electrical manifestations of the heart activity exceeds the preset number. More modern devices can distinguish between ventricular fibrillation and ventricular tachycardia
Ventricular tachycardia
Ventricular tachycardia is a tachycardia, or fast heart rhythm, that originates in one of the ventricles of the heart...

 (VT), and may try to pace the heart faster than its intrinsic rate in the case of VT, to try to break the tachycardia before it progresses to ventricular fibrillation. This is known as fast-pacing, overdrive pacing, or anti-tachycardia pacing (ATP). ATP is only effective if the underlying rhythm is ventricular tachycardia, and is never effective if the rhythm is ventricular fibrillation.

Many modern ICDs use a combination of various methods to determine if a fast rhythm is normal, ventricular tachycardia, or ventricular fibrillation.

Rate discrimination evaluates the rate of the lower chambers of the heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

 (the ventricle
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...

s) and compares it to the rate in the upper chambers of the heart (the atria
Atria may refer to:*Atrium , an anatomical structure of the heart*Atrium , a large open space within a building*Atria or Alpha Trianguli Australis, a star in the constellation Triangulum Australe...

). If the rate in the atria is faster than or equal to the rate in the ventricles, then the rhythm is most likely not ventricular in origin, and is usually more benign. If this is the case, the ICD does not provide any therapy.

Rhythm discrimination will see how regular a ventricular tachycardia is. Generally, ventricular tachycardia is regular. If the rhythm is irregular, it is usually due to conduction of an irregular rhythm that originates in the atria, such as atrial fibrillation.

Morphology discrimination checks the morphology of every ventricular beat and compares it to what the ICD believes is a normally conducted ventricular impulse for the patient. This normal ventricular impulse is often an average of a multiple of beats of the patient taken in the recent past.


The development of the ICD was pioneered at Sinai Hospital
Sinai Hospital
LifeBridge Health is a Baltimore area corporation operating several medical institutions. These most notably include Sinai Hospital of Baltimore, Northwest Hospital , and various nursing homes and medical office complexes.-Sinai Hospital:Sinai Hospital is a Baltimore, Maryland hospital originally...

 in Baltimore
Baltimore is the largest independent city in the United States and the largest city and cultural center of the US state of Maryland. The city is located in central Maryland along the tidal portion of the Patapsco River, an arm of the Chesapeake Bay. Baltimore is sometimes referred to as Baltimore...

 by a team including Michel Mirowski
Michel Mirowski
Dr. Michel Mirowski was born in Warsaw, Poland. He practiced medicine in Israel before coming to Sinai Hospital in Baltimore, Maryland. While there he collaborated with Dr. Morton Mower and later Dr...

, Morton Mower
Morton mower
Dr. Morton Mower is an American cardiologist and the co-inventor of the automatic implantable cardioverter defibrillator. He has served in several professional capacities at Sinai Hospital and Cardiac Pacemakers Inc. In 1996, he became the Chairman and Chief Executive Officer of Mower Research...

, and William Staewen. Mirowski teamed up with Mower and Staewen and together they commenced their research in 1969 but it was 11 years before they treated their first patient. Similar developmental work was carried out almost coincidentally by Schuder and colleagues at the University of Missouri
University of Missouri
The University of Missouri System is a state university system providing centralized administration for four universities, a health care system, an extension program, five research and technology parks, and a publishing press. More than 64,000 students are currently enrolled at its four campuses...


More than a decade of research went into the development of an implantable defibrillator that would automatically sense the onset of ventricular fibrillation and deliver an electric countershock within 15–20 seconds, converting the rhythm to sinus rhythm
Sinus rhythm
In medicine, sinus rhythm is the normal beating of the heart, as measured by an electrocardiogram . It has certain generic features that serve as hallmarks for comparison with normal ECGs.- ECG structure :...

. Improved versions were programmed to be able to detect ventricular tachycardia, often a forerunner of ventricular fibrillation. These were then called implantable cardioverters.

The work was commenced against much skepticism even by leading experts in the field of arrhythmias and sudden death. There was doubt that their ideas would ever become a clinical reality. In 1972 Bernard Lown
Bernard Lown
Bernard Lown, M.D. is the original developer of the defibrillator and is an internationally known peace activist. International Physicians for the Prevention of Nuclear War, an organization he helped to create, was awarded the 1985 Nobel Peace Prize for its work against nuclear proliferation...

, the inventor of the external defibrillator, stated in the journal Circulation
Circulation (journal)
Circulation is a scientific journal published by Lippincott Williams & Wilkins for the American Heart Association. The journal publishes articles related to research in and the practice of cardiovascular diseases, including observational studies, clinical trials, epidemiology, health services and...

- "The very rare patient who has frequent bouts of ventricular fibrillation is best treated in a coronary care unit and is better served by an effective antiarrhythmic program or surgical correction of inadequate coronary blood flow or ventricular malfunction. In fact, the implanted defibrillator system represents an imperfect solution in search of a plausible and practical application".

The problems to be overcome were the design of a system which would allow detection of ventricular fibrillation or ventricular tachycardia. Despite the lack of financial backing and grants, they persisted and the first device was implanted in February 1980 at Johns Hopkins Hospital
Johns Hopkins Hospital
The Johns Hopkins Hospital is the teaching hospital and biomedical research facility of Johns Hopkins University School of Medicine, located in Baltimore, Maryland . It was founded using money from a bequest by philanthropist Johns Hopkins...

 by Dr. Levi Watkins, Jr. Modern ICDs do not require a thoracotomy
Thoracotomy is an incision into the pleural space of the chest. It is performed by a surgeon, and, rarely, by emergency physicians, to gain access to the thoracic organs, most commonly the heart, the lungs, the esophagus or thoracic aorta, or for access to the anterior spine such as is necessary...

 and possess pacing, cardioversion, and defibrillation capabilities.

Internal cardioverter defibrillators have also been used twice in dogs to prevent sudden death from arrhythmia. The first defibrillator was implanted at Washington State University by a team of cardiologists led by Dr Lynne Johnson in 2003. The patient was a Boxer dog with life threatening arrhythmias from arrhythmogenic right ventricular cardiomyopathy, an inherited disease. On July 21, 2008, a second ICD was implanted in a 6-month-old German Shepherd dog with inherited ventricular arrhythmias. The 5-hour long surgery took place at Louisiana State University and was led by Dr Romain Pariaut. So far, these pets are the only two client-owned dogs that have received such a high-tech treatment.

Living with an ICD

People that have an implanted cardioverter-defibrillator can live full and happy lives. Usually the ICD improves the living conditions of a patient significantly. As with a pacemaker, living with an ICD does impose some restrictions on the person's lifestyle.

Quality of Life

Implantable cardioverter defibrillators have demonstrated clear life-saving benefits but concerns about patient acceptance and psychological adjustment to the ICD have been the focus of much research. Researchers including those from the field of cardiac psychology
Cardiac psychology
Cardiac psychology is a specialization of health psychology that focuses on the primary and secondary prevention of heart disease by incorporating strategies to address the emotional and behavioral barriers to lifestyle changes , and that seeks to enhance recovery in cardiac patients by means of...

 have concluded that the QoL of ICD patients is at least equal to, or better than those taking anti-arrhythmic medications
Antiarrhythmic agent
Antiarrhythmic agents are a group of pharmaceuticals that are used to suppress abnormal rhythms of the heart , such as atrial fibrillation, atrial flutter, ventricular tachycardia, and ventricular fibrillation....

. The largest study of examined 2,521 patients with stable heart failure in the SCD-HeFT trial. Results indicated that there were no differences between ICD treated and medication-treated groups at 30 months in patient reported QoL. Psychological adjustment following ICD implantation has also been well-studied. Anxiety
Anxiety is a psychological and physiological state characterized by somatic, emotional, cognitive, and behavioral components. The root meaning of the word anxiety is 'to vex or trouble'; in either presence or absence of psychological stress, anxiety can create feelings of fear, worry, uneasiness,...

 is a common psychological side effect
Side effect
In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequences of the use of a drug.Occasionally, drugs are...

 with approximately 13-38% of ICD patients reporting clinically significant anxiety. The primary etiological factors contributing to anxiety in ICD patients has not been determined, however. Depressive
Depression (mood)
Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless...

 symptoms are also common but incidence of these problems have shown to be similar to those observed in other cardiac patient groups with approximately 24-41% of patients with ICDs experiencing depressive symptoms.

Problems in psychosocial adjustment to ICDs, including the experience of anxiety, among spouses or other romantic partners are also prevalent. This phenomenon may be related, at least in part, to shared shock anxiety and avoidance of physical and sexual contact.

Physical activities

Almost all forms of physical activities can be performed by patients with an ICD. All forms of sports that do not pose a risk of damaging the ICD can be enjoyed by the patient. Special care should be placed not to put excessive strain on the shoulder, arm and torso area where the ICD is implanted. Doing so may damage the ICD or the leads going from the unit to the patient's heart.

Electronic equipment

As a general rule, all electronic equipment is safe to use for patients with an ICD if kept at relative small distance from the unit. Most electronic equipment such as cellphones, devices that generate radio waves or radio interference should be kept at least 15 centimetres (6 in) from the ICD.

Electronic equipment used in a professional environment or equipment using large magnets or generating magnetic fields must be avoided by patients with an ICD. Both the magnetic fields and the EMI (Electromagnetic Interference) in an MRI scanner can interfere with the correct working of the ICD.
As with other metallic objects, an ICD is a contraindication
In medicine, a contraindication is a condition or factor that serves as a reason to withhold a certain medical treatment.Some contraindications are absolute, meaning that there are no reasonable circumstances for undertaking a course of action...

 to the use of magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...

. Experiments are on the way for solving this kind of problem. For example Medtronic showed interesting results with a pacemaker.

Clinical trials

A number of clinical trials have demonstrated the superiority of the ICD over AAD (antiarrhythmic drugs) in the prevention of death from malignant arrhythmias.
The SCD-HeFT trial (published in 2005) showed a significant all-cause mortality benefit for patients with ICD. Congestive heart failure
Congestive heart failure
Heart failure often called congestive heart failure is generally defined as the inability of the heart to supply sufficient blood flow to meet the needs of the body. Heart failure can cause a number of symptoms including shortness of breath, leg swelling, and exercise intolerance. The condition...

 patients that were implanted with an ICD had an all-cause death risk 23% lower than placebo and an absolute decrease in mortality of 7.2 percentage points after five years in the overall population.1
Reporting in 1999, the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial consisted of 1,016 patients, and deaths in those treated with AAD were more frequent (n=122) compared with deaths in the ICD groups (n=80, p < 0.001)http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=10551706&query_hl=5. In 2002 the MADITII
Multicenter Automatic Defibrillator Implantation Trial
Multicenter Automatic Defibrillator Implantation Trial and MADIT II are implantable cardioverter defibrillator trials which investigate whether prophylactic ICD therapy in moderately high-risk coronary patients would significantly reduce death compared with patients treated with conventional...

 trial showed benefit of ICD treatment in patients after myocardial infarction with reduced left ventricular function (EF<30).

Initially ICDs were implanted via thoracotomy with defibrillator patches applied to the epicardium
Epicardium describes the outer layer of heart tissue . When considered as a part of the pericardium, it is the inner layer, or visceral pericardium, continuous with the serous layer....

 or pericardium
The pericardium is a double-walled sac that contains the heart and the roots of the great vessels.-Layers:...

. The device was attached via subcutaneous and transvenous leads to the device contained in a subcutaneous abdominal wall pocket. The device itself acts as an electrode. Most ICDs nowadays are implanted transvenously with the devices placed in the left pectoral region similar to pacemakers. Intravascular spring or coil electrodes are used to defibrillate. The devices have become smaller and less invasive as the technology advances. Current ICDs weigh only 70 grams and are about 12.9 mm thick.

A recent study by Birnie et al. at the University of Ottawa Heart Institute has demonstrated that ICDs are underused in both the United States and Canada. An accompanying editorial by Dr. Chris Simpson of Queen's University explores some of the economic, geographic, social and political reasons for this.

See also

  • CPR
    Cardiopulmonary resuscitation
    Cardiopulmonary resuscitation is an emergency procedure which is performed in an effort to manually preserve intact brain function until further measures are taken to restore spontaneous blood circulation and breathing in a person in cardiac arrest. It is indicated in those who are unresponsive...

  • Advanced cardiac life support
    Advanced cardiac life support
    Advanced cardiac life support or Advanced Cardiovascular Life Support refers to a set of clinical interventions for the urgent treatment of cardiac arrest and other life threatening medical emergencies, as well as the knowledge and skills to deploy those interventions.Extensive medical knowledge...

  • Cardioversion
    Cardioversion is a medical procedure by which an abnormally fast heart rate or cardiac arrhythmia is converted to a normal rhythm, using electricity or drugs. Synchronized electrical cardioversion uses a therapeutic dose of electric current to the heart, at a specific moment in the cardiac cycle...

  • Defibrillation
    Defibrillation is a common treatment for life-threatening cardiac arrhythmias, ventricular fibrillation and pulseless ventricular tachycardia. Defibrillation consists of delivering a therapeutic dose of electrical energy to the affected heart with a device called a defibrillator...

  • Artificial pacemaker
    Artificial pacemaker
    A pacemaker is a medical device that uses electrical impulses, delivered by electrodes contacting the heart muscles, to regulate the beating of the heart...

  • Boston Scientific
    Boston Scientific
    The Boston Scientific Corporation , is a worldwide developer, manufacturer and marketer of medical devices whose products are used in a range of interventional medical specialties, including interventional cardiology, peripheral interventions, neuromodulation, neurovascular intervention,...

  • Cameron Health
    Cameron Health
    Cameron Health is a medical device developer based in San Clemente, California, USA. Cameron Health has its European office, Cameron Health BV, in Arnhem, The Netherlands. The privately-held company's focus is on a new generation of minimally invasive implantable cardioverter-defibrillator which...

  • Medtronic
    Medtronic, Inc. , based in suburban Minneapolis, Minnesota, is the world's largest medical technology company and is a Fortune 500 company.- History :...

  • St Jude Medical
  • Sorin Group
    Sorin Group
    The Sorin Group is a medical products group based in Italy, with significant operations in France, the United States, and Japan, specializing in cardiac devices...

  • Biotronik
    Biotronik is a privately-held multinational biomedical technology company headquartered in Berlin, Germany. Biotronik developed the first German cardiac pacemaker in 1963 and pioneered in the creation of remotely-monitored implanted cardiac devices...

  • Wearable Cardioverter Defibrillator
    Wearable cardioverter defibrillator
    The wearable cardioverter defibrillator is worn by patients at risk for sudden cardiac arrest , allowing their physician time to assess their long-term arrhythmic risk and make appropriate plans....

  • Samuel Sears
    Samuel Sears
    Samuel F. Sears, Jr., Ph.D. is a professor of health psychology at East Carolina University in Greenville, NC.- Early life and clinical training :...

External links