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Artificial pacemaker

Artificial pacemaker

Overview


A pacemaker is a medical device
Medical device
A medical device is a product which is used for medical purposes in patients, in diagnosis, therapy or surgery . Whereas medicinal products achieve their principal action by pharmacological, metabolic or immunological means. Medical devices act by other means like physical, mechanical, thermal,...

 that uses electrical impulses, delivered by electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

s contacting the heart muscles, to regulate the beating of the heart
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 primary purpose of a pacemaker is to maintain an adequate heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....

, either because of the heart's native pacemaker
Sinoatrial node
The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...

 is not fast enough, or there is a block in the heart's electrical conduction system
Electrical conduction system of the heart
The normal intrinsic electrical conduction of the heart allows electrical propagation to be transmitted from the Sinoatrial Node through both atria and forward to the Atrioventricular Node. Normal/baseline physiology allows further propagation from the AV node to the ventricle or Purkinje Fibers...

. Modern pacemakers are externally programmable and allow the cardiologist to select the optimum pacing modes for individual patients.
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Encyclopedia


A pacemaker is a medical device
Medical device
A medical device is a product which is used for medical purposes in patients, in diagnosis, therapy or surgery . Whereas medicinal products achieve their principal action by pharmacological, metabolic or immunological means. Medical devices act by other means like physical, mechanical, thermal,...

 that uses electrical impulses, delivered by electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

s contacting the heart muscles, to regulate the beating of the heart
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 primary purpose of a pacemaker is to maintain an adequate heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....

, either because of the heart's native pacemaker
Sinoatrial node
The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...

 is not fast enough, or there is a block in the heart's electrical conduction system
Electrical conduction system of the heart
The normal intrinsic electrical conduction of the heart allows electrical propagation to be transmitted from the Sinoatrial Node through both atria and forward to the Atrioventricular Node. Normal/baseline physiology allows further propagation from the AV node to the ventricle or Purkinje Fibers...

. Modern pacemakers are externally programmable and allow the cardiologist to select the optimum pacing modes for individual patients. Some combine a pacemaker and defibrillator
Implantable cardioverter-defibrillator
An implantable cardioverter-defibrillator is a small battery-powered electrical impulse generator which is implanted in patients who are at risk of sudden cardiac death due to ventricular fibrillation and ventricular tachycardia. The device is programmed to detect cardiac arrhythmia and correct it...

 in a single implantable device. Others have multiple electrodes stimulating differing positions within the heart to improve synchronisation
Synchronization
Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....

 of the lower chambers
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...

 of the heart.

History



In 1899, J A McWilliam reported in the British Medical Journal of his experiments in which application of an electrical impulse to the human heart in asystole
Asystole
In medicine, asystole is a state of no cardiac electrical activity, hence no contractions of the myocardium and no cardiac output or blood flow...

 caused a 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...

 contraction and that a heart rhythm of 60-70 beats per minute could be evoked by impulses applied at spacings equal to 60-70/minute.

In 1926, Dr Mark C Lidwell of the Royal Prince Alfred Hospital
Royal Prince Alfred Hospital
The Royal Prince Alfred Hospital is a major public teaching hospital in Sydney, Australia, located on Missenden Road in Camperdown...

 of Sydney, supported by physicist Edgar H Booth of the University of Sydney
University of Sydney
The University of Sydney is a public university located in Sydney, New South Wales. The main campus spreads across the suburbs of Camperdown and Darlington on the southwestern outskirts of the Sydney CBD. Founded in 1850, it is the oldest university in Australia and Oceania...

, devised a portable apparatus which "plugged into a lighting point" and in which "One pole was applied to a skin pad soaked in strong salt solution" while the other pole "consisted of a needle insulated except at its point, and was plunged into the appropriate cardiac chamber". "The pacemaker rate was variable from about 80 to 120 pulses per minute, and likewise the voltage variable from 1.5 to 120 volts" In 1928, the apparatus was used to revive a stillborn
Stillbirth
A stillbirth occurs when a fetus has died in the uterus. The Australian definition specifies that fetal death is termed a stillbirth after 20 weeks gestation or the fetus weighs more than . Once the fetus has died the mother still has contractions and remains undelivered. The term is often used in...

 infant at Crown Street Women's Hospital, Sydney
Crown Street Women's Hospital, Sydney
Crown Street Women's Hospital was once the largest maternity hospital in Sydney, New South Wales, Australia. It was located at 351 Crown Street , Surry Hills....

 whose heart continued "to beat on its own accord", "at the end of 10 minutes" of stimulation.

In 1932, American physiologist Albert Hyman
Albert Hyman
Albert S. Hyman , a New York cardiologist, together with his brother Charles, constructed in 1930-1932 an electro-mechanical device which was one of the earliest artificial pacemakers...

, working independently, described an electro-mechanical instrument of his own, powered by a spring-wound hand-cranked motor. Hyman himself referred to his invention as an "artificial pacemaker", the term continuing in use to this day.

An apparent hiatus in publication of research conducted between the early 1930s and World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 may be attributed to the public perception of interfering with nature by 'reviving the dead'. For example, "Hyman did not publish data on the use of his pacemaker in humans because of adverse publicity, both among his fellow physicians, and due to newspaper reporting at the time. Lidwell may have been aware of this and did not proceed with his experiments in humans".

An external pacemaker was designed and built by the Canadian electrical engineer John Hopps
John Alexander Hopps
John Alexander "Jack" Hopps, Canadian, was one of the pioneers of the artificial pacemaker and is known as the "father of biomedical engineering in Canada"....

 in 1950 based upon observations by cardio-thoracic surgeon Wilfred Gordon Bigelow at Toronto General Hospital
Toronto General Hospital
The Toronto General Hospital , is a part of the University Health Network, and a major teaching hospital in downtown Toronto, Ontario. It is located in the Discovery District, directly north of the Hospital for Sick Children, across Gerrard Street West, and east of Princess Margaret Hospital and...

 . A substantial external device using vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

 technology to provide transcutaneous pacing
Transcutaneous pacing
Transcutaneous pacing is a temporary means of pacing a patient's heart during a medical emergency. It is accomplished by delivering pulses of electric current through the patient's chest, which stimulates the heart to contract....

, it was somewhat crude and painful to the patient in use and, being powered from an AC wall socket, carried a potential hazard of electrocution
Electric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....

 of the patient by inducing 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...

.

A number of innovators, including Paul Zoll
Paul Zoll
Paul Maurice Zoll was a cardiologist and one of the pioneers in the development of the cardiac pacemaker and cardiac defibrillator.-External links:*...

, made smaller but still bulky transcutaneous pacing
Transcutaneous pacing
Transcutaneous pacing is a temporary means of pacing a patient's heart during a medical emergency. It is accomplished by delivering pulses of electric current through the patient's chest, which stimulates the heart to contract....

 devices in the following years using a large rechargeable battery as the power supply.

In 1957, Dr. William L. Weirich published the results of research performed at the University of Minnesota
University of Minnesota
The University of Minnesota, Twin Cities is a public research university located in Minneapolis and St. Paul, Minnesota, United States. It is the oldest and largest part of the University of Minnesota system and has the fourth-largest main campus student body in the United States, with 52,557...

. These studies demonstrated the restoration of heart rate, cardiac output and mean aortic pressures in animal subjects with complete heart block
Heart block
A heart block can be a blockage at any level of the electrical conduction system of the heart .* Blocks that occur within the sinoatrial node are described as SA nodal blocks....

 through the use of a myocardial electrode. This effective control of postsurgical heart block proved to be a significant contribution to decreasing mortality
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....

 of open heart surgery
Open Heart Surgery
Open Heart Surgery was released on August 8, 2000 by rock band Virginwool. The band signed to Breaking/Atlantic Records after initially beginning signed to Universal Records. The album was produced and mixed by Brad Wood....

 in this time period.

In 1958 Colombian electrical engineer Jorge Reynolds Pombo constructed an external pacemaker, similar to those of Hopps and Zoll, weighing 45 kg and powered by a 12 volt auto battery, but connected to electrodes attached to the heart. This apparatus was successfully used to sustain a 70 year old priest, Gerardo Florez.

The development of the silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

 and its first commercial availability in 1956 was the pivotal event which led to rapid development of practical cardiac pacemaking.

In 1958, engineer Earl Bakken
Earl Bakken
Earl E. Bakken is an American engineer, businessman and philanthropist of Dutch and Norwegian American ancestry...

 of Minneapolis, Minnesota, produced the first wearable external pacemaker for a patient of Dr. C. Walton Lillehei
C. Walton Lillehei
Clarence Walton Lillehei , was an American surgeon who pioneered open-heart surgery, as well as numerous techniques, equipment and prostheses for cardiothoracic surgery.-Background:...

. This transistorised pacemaker, housed in a small plastic box, had controls to permit adjustment of pacing heart rate and output voltage and was connected to electrode leads which passed through the skin of the patient to terminate in electrodes attached to the surface of the myocardium of the heart.

The first clinical implantation into a human of a fully implantable pacemaker was in 1958 at the Karolinska Institute in Solna, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

, using a pacemaker designed by Rune Elmqvist
Rune Elmqvist
Rune Elmqvist developed the first implantable pacemaker in 1958, working under the direction of Åke Senning, senior physician and cardiac surgeon at the Karolinska University Hospital in Solna, Sweden....

 and surgeon Åke Senning
Åke Senning
Åke Senning was a pioneering Swedish cardiac surgeon, who implanted the first human implantable cardiac pacemaker in 1958, invented the Senning operation, and contributed to many other advances....

, connected to electrodes attached to the myocardium of the heart by thoracotomy
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...

. The device failed after three hours. A second device was then implanted which lasted for two days. The world's first implantable pacemaker patient, Arne Larsson, went on to receive 26 different pacemakers during his lifetime. He died in 2001, at the age of 86, outliving the inventor as well as the surgeon.

In 1959, temporary transvenous pacing
Transvenous pacing
Transvenous cardiac pacing, also called endocardial pacing, is a potentially life saving intervention used primarily to correct profound bradycardia. It can be used to treat symptomatic bradycardias that do not respond to transcutaneous pacing or to drug therapy...

 was first demonstrated by Furman et al. in which the catheter
Catheter
In medicine, a catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization...

 electrode was inserted via the patient's basilic vein
Basilic vein
In human anatomy, the basilic vein is a large superficial vein of the upper limb that helps drain parts of hand and forearm. It originates on the medial side of the dorsal venous network of the hand, and it travels up the base of the forearm and arm...

.

In February 1960, an improved version of the Swedish Elmqvist design was implanted in Montevideo
Montevideo
Montevideo is the largest city, the capital, and the chief port of Uruguay. The settlement was established in 1726 by Bruno Mauricio de Zabala, as a strategic move amidst a Spanish-Portuguese dispute over the platine region, and as a counter to the Portuguese colony at Colonia del Sacramento...

, Uruguay
Uruguay
Uruguay ,officially the Oriental Republic of Uruguay,sometimes the Eastern Republic of Uruguay; ) is a country in the southeastern part of South America. It is home to some 3.5 million people, of whom 1.8 million live in the capital Montevideo and its metropolitan area...

 in the Casmu Hospital by Doctors Fiandra and Rubio. That device lasted until the patient died of other ailments, 9 months later. The early Swedish-designed devices used rechargeable batteries, which were charged by an induction coil from the outside.

Implantable pacemakers constructed by engineer Wilson Greatbatch
Wilson Greatbatch
Wilson Greatbatch was an American engineer and inventor whois most widely known as the inventor of the implantable cardiac pacemaker...

 entered use in humans from April 1960 following extensive animal testing
Animal testing
Animal testing, also known as animal experimentation, animal research, and in vivo testing, is the use of non-human animals in experiments. Worldwide it is estimated that the number of vertebrate animals—from zebrafish to non-human primates—ranges from the tens of millions to more than 100 million...

. The Greatbatch innovation varied from the earlier Swedish devices in using primary cells (mercury battery
Mercury battery
A mercury battery is a non-rechargeable electrochemical battery, a primary cell. Due to the content of mercury, and the resulting environmental concerns, the sale of mercury batteries is banned in many countries. Both ANSI and IEC have withdrawn standards for mercury batteries...

) as the energy source. The first patient lived for a further 18 months.

The first use of transvenous pacing
Transvenous pacing
Transvenous cardiac pacing, also called endocardial pacing, is a potentially life saving intervention used primarily to correct profound bradycardia. It can be used to treat symptomatic bradycardias that do not respond to transcutaneous pacing or to drug therapy...

 in conjunction with an implanted pacemaker was by Parsonnet in the USA, Lagergren in Sweden and Jean-Jaques Welti in France in 1962-63.
The transvenous, or pervenous, procedure involved incision of a vein into which was inserted the catheter
Catheter
In medicine, a catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization...

 electrode lead under fluoroscopic guidance, until it was lodged within the trabeculae of the right ventricle. This method was to become the method of choice by the mid-1960s.

The preceding implantable devices all suffered from the unreliability and short lifetime of the available primary cell technology which was mainly that of the mercury battery
Mercury battery
A mercury battery is a non-rechargeable electrochemical battery, a primary cell. Due to the content of mercury, and the resulting environmental concerns, the sale of mercury batteries is banned in many countries. Both ANSI and IEC have withdrawn standards for mercury batteries...

.
In the late 1960s, several companies, including ARCO in the USA, developed isotope powered pacemakers, but this development was overtaken by the development in 1971 of the lithium-iodide cell by Wilson Greatbatch
Wilson Greatbatch
Wilson Greatbatch was an American engineer and inventor whois most widely known as the inventor of the implantable cardiac pacemaker...

. Lithium-iodide or lithium anode cells became the standard for future pacemaker designs.

A further impediment to reliability of the early devices was the diffusion of water vapour from the body fluids through the epoxy
Epoxy
Epoxy, also known as polyepoxide, is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives....

 resin encapsulation affecting the electronic circuitry. This phenomenon was overcome by encasing the pacemaker generator in an hermetically sealed metal case, initially by Telectronics
Telectronics
Telectronics Pty Ltd was an Australian company best known for its role in developing the pacemaker. In 1988 the business was acquired by Pacific Dunlop...

 of Australia in 1969 followed by Cardiac Pacemakers Inc of Minneapolis in 1972. This technology, using titanium as the encasing metal, became the standard by the mid-1970s.

Others who contributed significantly to the technological development of the pacemaker in the pioneering years were Bob Anderson of Medtronic
Medtronic
Medtronic, Inc. , based in suburban Minneapolis, Minnesota, is the world's largest medical technology company and is a Fortune 500 company.- History :...

 Minneapolis, J.G (Geoffrey) Davies of St George's Hospital
St George's Hospital
Founded in 1733, St George’s Hospital is one of the UK's largest teaching hospitals. It shares its main hospital site in Tooting, England with the St George's, University of London which trains NHS staff and carries out advanced medical research....

 London, Barouh Berkovits
Barouh Berkovits
Barouh Berkovits is one of the pioneers of Bio-engineering, particularly the cardiac defibrillator and artificial cardiac pacemaker.-External links:*...

 and Sheldon Thaler of American Optical, Geoffrey Wickham
Geoffrey Wickham
Geoffrey Gordon Wickham AO MIIE was one of the pioneers of cardiac pacemaking, born at Camperdown, Victoria, Australia to dairy farmer parents on 28 October 1933.In 1963 he co-founded the medical instruments company Telectronics Pty Ltd in Sydney, and served as the company's Technical Director from...

 of Telectronics
Telectronics
Telectronics Pty Ltd was an Australian company best known for its role in developing the pacemaker. In 1988 the business was acquired by Pacific Dunlop...

 Australia, Walter Keller
Walter Keller
Walter Keller is a mathematician, physicist, researcher, designer, and inventor. He designed and holds the patent on the first implantable atrial synchronous heart pacemaker; he designed a demand circuit critical to the controls of the artificial heart; and he pioneered the first remotely...

 of Cordis
Cordis (medical)
Cordis is a medical device company owned by Johnson & Johnson. The company was founded in Miami in 1959 and is currently headquartered in Bridgewater Township, New Jersey.Cordis' products include stents, distal protection devices, catheters, and guidewires....

 Corp. of Miami, Hans Thornander
Hans Thornander
Hans Thornander was one of the pioneers of the cardiac pacemaker....

 who joined previously mentioned Rune Elmquist of Elema-Schonander in Sweden, Janwillem van den Berg
Janwillem van den Berg
Janwillem van den Berg was a Dutch speech scientist and medical physicist who played a major role in establishing the myoelastic-aerodynamic theory of voice production...

 of Holland and Anthony Adducci
Anthony Adducci
Anthony J. Adducci was a pioneer of the medical device industry in Minnesota. He is best known for co-founding Guidant Corp. precursor Cardiac Pacemakers, inc., now part of Boston Scientific, the company that manufactured the world's first lithium battery powered artificial pacemaker.-Early...

 of Cardiac Pacemakers Inc.Guidant
Guidant
Guidant Corporation, part of Boston Scientific and Abbott Labs, designs and manufactures artificial pacemakers, implantable defibrillators, stents, and other cardiovascular medical products. Their company headquarters is located in Indianapolis, Indiana. Their main competitors are Medtronic, St...

.

Methods of pacing



Percussive pacing


Percussive pacing, also known as transthoracic mechanical pacing, is the use of the closed fist, usually on the left lower edge of the sternum over the right ventricle in the vena cava, striking from a distance of 20 – 30 cm to induce a ventricular beat (the British Journal of Anesthesia suggests this must be done to raise the ventricular pressure to 10 - 15mmHg to induce electrical activity). This is an old procedure used only as a life saving means until an electrical pacemaker is brought to the patient.

Transcutaneous pacing


Transcutaneous pacing (TCP), also called external pacing, is recommended for the initial stabilization of hemodynamically significant bradycardia
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...

s of all types. The procedure is performed by placing two pacing pads on the patient's chest, either in the anterior/lateral position or the anterior/posterior position. The rescuer selects the pacing rate, and gradually increases the pacing current (measured in mA) until electrical capture (characterized by a wide QRS complex with a tall, broad T wave on the ECG
Electrocardiogram
Electrocardiography is a transthoracic interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body...

) is achieved, with a corresponding pulse. Pacing artifact on the ECG
Electrocardiogram
Electrocardiography is a transthoracic interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body...

 and severe muscle twitching may make this determination difficult. External pacing should not be relied upon for an extended period of time. It is an emergency procedure that acts as a bridge until transvenous pacing or other therapies can be applied.

Epicardial pacing (temporary)




Temporary epicardial pacing is used during open heart surgery should the surgical procedure create atrio ventricular block. The electrodes are placed in contact with the outer wall of the ventricle (epicardium) to maintain satisfactory cardiac output until a temporary transvenous electrode has been inserted.

Transvenous pacing (temporary)



Transvenous pacing, when used for temporary pacing, is an alternative to transcutaneous pacing. A pacemaker wire is placed into a vein, under sterile conditions, and then passed into either the right atrium or right ventricle. The pacing wire is then connected to an external pacemaker outside the body. Transvenous pacing is often used as a bridge to permanent pacemaker placement. It can be kept in place until a permanent pacemaker is implanted or until there is no longer a need for a pacemaker and then it is removed.

Permanent pacing



Permanent pacing with an implantable pacemaker involves transvenous placement of one or more pacing electrodes within a chamber, or chambers, of the heart. The procedure is performed by incision of a suitable vein into which the electrode lead is inserted and passed along the vein, through the valve of the heart, until positioned in the chamber. The procedure is facilitated by fluoroscopy
Fluoroscopy
Fluoroscopy is an imaging technique commonly used by physicians to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope. In its simplest form, a fluoroscope consists of an X-ray source and fluorescent screen between which a patient is placed...

 which enables the physician or cardiologist to view the passage of the electrode lead. After satisfactory lodgement of the electrode is confirmed, the opposite end of the electrode lead is connected to the pacemaker generator.

There are three basic types of permanent pacemakers, classified according to the number of chambers
Heart chamber
aHeart chamber is a general term used to refer to any chambers of the mammalian heart. The heart consists of four chambers: the right and left atrium and the right and left ventricle. The top chambers are connected to the bottom chambers by valves and are separated by the coronary sulcus...

 involved and their basic operating mechanism:
  • Single-chamber pacemaker. In this type, only one pacing lead is placed into a chamber of the heart, either the atrium or 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...

    .
  • Dual-chamber pacemaker. Here, wires are placed in two chambers of the heart. One lead paces the atrium and one paces the ventricle. This type more closely resembles the natural pacing of the heart by assisting the heart in coordinating the function between the atria and ventricles.
  • Rate-responsive pacemaker. This pacemaker has sensors that detect changes in the patient's physical activity and automatically adjust the pacing rate to fulfill the body's metabolic needs.


The pacemaker generator is a hermetically sealed device containing a power source, usually a lithium battery
Lithium battery
Lithium batteries are disposable batteries that have lithium metal or lithium compounds as an anode. Depending on the design and chemical compounds used, lithium cells can produce voltages from 1.5 V to about 3.7 V, over twice the voltage of an ordinary zinc–carbon battery or alkaline battery...

, a sensing amplifier which processes the electrical manifestation of naturally occurring heart beats as sensed by the heart electrodes, the computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 logic for the pacemaker and the output circuitry which delivers the pacing impulse to the electrodes.

Most commonly, the generator is placed below the subcutaneous fat of the chest wall, above the muscles and bones of the chest. However, the placement may vary on a case by case basis.

The outer casing of pacemakers is so designed that it will rarely be rejected by the body's immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

. It is usually made of titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

, which is inert in the body.

Basic function


Modern pacemakers usually have multiple functions. The most basic form monitors the heart's native electrical rhythm. When the pacemaker fails to sense a heartbeat within a normal beat-to-beat time period, it will stimulate the ventricle of the heart with a short low voltage pulse. This sensing and stimulating activity continues on a beat by beat basis.

The more complex forms include the ability to sense and/or stimulate both the atrial and ventricular chambers.
The revised NASPE/BPEG generic code for antibradycardia pacing
I II III IV V
Chamber(s) paced Chamber(s) sensed Response to sensing Rate modulation Multisite pacing
O = None O = None O = None O = None O = None
A = Atrium A = Atrium T = Triggered R = Rate modulation A = Atrium
V = Ventricle V = Ventricle I = Inhibited V = Ventricle
D = Dual (A+V) D = Dual (A+V) D = Dual (T+I) D = Dual (A+V)


From this the basic ventricular "on demand" pacing mode is VVI or with automatic rate adjustment for exercise VVIR - this mode is suitable when no synchronization with the atrial beat is required, as in atrial fibrillation. The equivalent atrial pacing mode is AAI or AAIR which is the mode of choice when atrioventricular conduction is intact but the natural pacemaker the sinoatrial node
Sinoatrial node
The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...

 is unreliable - sinus node disease (SND) or sick sinus syndrome
Sick sinus syndrome
Sick sinus syndrome, also called sinus node dysfunction, is a group of abnormal heart rhythms presumably caused by a malfunction of the sinus node, the heart's primary pacemaker...

. Where the problem is atrioventricular block
Atrioventricular block
An atrioventricular block involves the impairment of the conduction between the atria and ventricles of the heart.The causes of pathological AV block are varied and include ischaemia, infarction, fibrosis or drugs. Certain AV blocks can also be found as normal variants, such as in athletes or...

 (AVB) the pacemaker is required to detect (sense) the atrial beat and after a normal delay (0.1-0.2 seconds) trigger a ventricular beat, unless it has already happened - this is VDD mode and can be achieved with a single pacing lead with electrodes in the right atrium (to sense) and ventricle (to sense and pace). These modes AAIR and VDD are unusual in the US but widely used in Latin America and Europe. The DDDR mode is most commonly used as it covers all the options though the pacemakers require separate atrial and ventricular leads and are more complex, requiring careful programming of their functions for optimal results.

Biventricular pacing (BVP)





A biventricular pacemaker, also known as CRT (cardiac resynchronization therapy) is a type of pacemaker that can pace both the septal and lateral walls of the left ventricle. By pacing both sides of the left ventricle, the pacemaker can resynchronize a heart whose opposing walls do not contract in synchrony, which occurs in approximately 25-50 % of heart failure patients.
CRT devices have at least two leads, one in the right ventricle to stimulate the septum, and another inserted through the coronary sinus
Coronary sinus
The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the myocardium of the heart. It is present in all mammals, including humans...

 to pace the lateral wall of the left ventricle. Often, for patients in normal sinus rhythm, there is also a lead in the right atrium to facilitate synchrony with the atrial contraction. Thus, timing between the atrial and ventricular contractions, as well as between the septal and lateral walls of the left ventricle can be adjusted to achieve optimal cardiac function.
CRT devices have been shown to reduce mortality and improve quality of life in patients with heart failure symptoms; a LV ejection fraction less than or equal to 35% and QRS duration on EKG of 120 msec or greater. CRT can be combined with an implantable cardioverter-defibrillator (ICD).

Advancements in function



A major step forward in pacemaker function has been to attempt to mimic nature by utilizing various inputs to produce a rate-responsive pacemaker using parameters such as the QT interval
QT interval
In cardiology, the QT interval is a measure of the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle. In general, the QT interval represents electrical depolarization and repolarization of the left and right ventricles...

, pO2 - pCO2 (dissolved oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 or carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 levels) in the arterial-venous system, physical activity as determined by an accelerometer
Accelerometer
An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...

, body temperature, ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

 levels, adrenaline, etc.
Instead of producing a static, predetermined heart rate, or intermittent control, such a pacemaker, a 'Dynamic Pacemaker', could compensate for both actual respiratory loading and potentially anticipated respiratory loading. The first dynamic pacemaker was invented by Dr. Anthony Rickards of the National Health Hospital, London, UK, in 1982.

Dynamic pacemaking technology could also be applied to future artificial hearts. Advances in transitional tissue welding would support this and other artificial organ/joint/tissue replacement efforts.
Stem cells may or may not be of interest to transitional tissue welding.

Many advancements have been made to improve the control of the pacemaker once implanted. Many of these have been made possible by the transition to microprocessor controlled pacemakers. Pacemakers that control not only the ventricles but the atria as well have become common. Pacemakers that control both the atria and ventricles are called dual-chamber pacemakers. Although these dual-chamber models are usually more expensive, timing the contractions of the atria to precede that of the ventricles improves the pumping efficiency of the heart and can be useful in congestive heart failure.

Rate responsive pacing allows the device to sense the physical activity of the patient and respond appropriately by increasing or decreasing the base pacing rate via rate response algorithms.

The DAVID trials have shown that unnecessary pacing of the right ventricle can exacerbate heart failure and increases the incidence of atrial fibrillation. The newer dual chamber devices can keep the amount of right ventricle pacing to a minimum and thus prevent worsening of the heart disease.

Insertion


A pacemaker is typically inserted into the patient through a simple surgery using either local anesthetic
Local anesthetic
A local anesthetic is a drug that causes reversible local anesthesia, generally for the aim of having local analgesic effect, that is, inducing absence of pain sensation, although other local senses are often affected as well...

 or a general anesthetic. The patient may be given a drug for relaxation before the surgery as well. An antibiotic is typically administered to prevent infection. In most cases the pacemaker is inserted in the left shoulder area where an incision is made below the collar bone creating a small pocket where the pacemaker is actually housed in the patient's body. The lead or leads (the number of leads varies depending on the type of pacemaker) are fed into the heart through a large vein using a fluoroscope to monitor the progress of lead insertion. The Right Ventricular lead would be positioned away from the apex (tip) of the right ventricle and up on the inter ventricular septum, below the outflow tract, to prevent deterioration of the strength of the heart. The actual surgery may take about 30 to 90 minutes.

Following surgery the patient should exercise reasonable care about the wound as it heals. There is a followup session during which the pacemaker is checked using a "programmer" that can communicate with the device and allows a health care professional to evaluate the system's integrity and determine the settings such as pacing voltage output. The patient should have the strength of their heart analyzed frequently with echocardiography, every 1 or 2 years, to make sure the that placement of the right ventricular lead has not lead to weakening of the left ventricle.

The patient may want to consider some basic preparation before the surgery. The most basic preparation is that people who have body hair on the chest may want to remove the hair by clipping just prior to surgery or using a depilatory agent (preoperative shaving has been on the decline as it can cause skin breakage and increase infection risk of any surgical procedure) as the surgery will involve bandages and monitoring equipment to be afixed to the body.

Since a pacemaker uses batteries, the device itself will need replacement as the batteries lose power. Device replacement is usually a simpler procedure than the original insertion as it does not normally require leads to be implanted. The typical replacement requires a surgery in which an incision is made to remove the existing device, the leads are removed from the existing device, the leads are attached to the new device, and the new device is inserted into the patient's body replacing the previous device.

Pacemaker patient identification card


International pacemaker patient identification cards carry information such as patient data (among others, symptom primary, ECG, aetiology), pacemaker center (doctor, hospital), IPG
IPG
IPG may refer to:*Interactive program guide, another name for an electronic program guide, a graphical user interface for cable TV boxes, satellite TV boxes, VCRs, DVRs and televisions which displays programming information...

(rate, mode
Mode
Mode may mean:* Transport mode, a means of transportation* Block cipher modes of operation, in cryptography* A technocomplex of stone tools...

, date of implantation, manufacturer
Manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...

, type) and lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

.

Periodic pacemaker checkups



Once the pacemaker is implanted, it is periodically checked to ensure the device is operational and performing appropriately. Depending on the frequency set by the following physician, the device can be checked as often as is necessary. Routine pacemaker checks are typically done in-office every six (6) months, though will vary depending upon patient/device status and remote monitoring availability.

At the time of in-office follow-up, the device will be interrogated to perform diagnostic testing. These tests include:
  • Sensing: the ability of the device to "see" intrinsic cardiac activity (Atrial and ventricular depolarization).
  • Impedance: A test to measure lead integrity. Large and/or sudden increases in impedance can be indicative of a lead fracture while large and/or sudden decreases in impedance can signify a breach in lead insulation.
  • Threshold: this test confirms the minimum amount of energy (Both volts and pulse width) required to reliably depolarize (capture) the chamber being tested. Determining the threshold allows the Allied Professional, Representative, or Physician to program an output that recognizes an appropriate safety margin while optimizing device longevity.


As modern pacemakers are "on-demand", meaning that they only pace when necessary, device longevity is affected by how much it is utilized. Other factors affecting device longevity include programmed output and algorithms (features) causing a higher level of current drain from the battery.

An additional aspect of the in-office check is to examine any events that were stored since the last follow-up. These are typically stored based on specific criteria set by the physician and specific to the patient. Some devices have the availability to display intracardiac electrograms of the onset of the event as well as the event itself. This is especially helpful in diagnosing the cause or origin of the event and making any necessary programming changes.

Lifestyle considerations


A patient's lifestyle is usually not modified to any great degree after insertion of a pacemaker. There are a few activities that are unwise such as full contact sports and activities that involve intense magnetic fields.

The pacemaker patient may find that some types of everyday actions need to be modified. For instance, the shoulder harness of a vehicle seatbelt may be uncomfortable if the harness should fall across the pacemaker insertion site.

Any kind of an activity that involves intense magnetic fields should be avoided. This includes activities such as arc welding
Arc welding
Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct or alternating current, and consumable or non-consumable electrodes...

 possibly, with certain types of equipment, or maintaining heavy equipment that may generate intense magnetic fields (such as an MRI (Magnetic Resonance Imaging Machine)).

However, in February 2011 the FDA approved a new pacemaker device called the Revo MRI SureScan which is the first to be proven safe for MRI use. There are several limitations to its use including certain patients qualifications, body parts, and scan settings.

A 2008 U.S. study has found that the magnets in some portable music players, when placed within an inch of pacemakers, may cause interference.

Some medical procedures may require the use of antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...

s to be administered before the procedure. The patient should inform all medical personnel that they have a pacemaker. Some standard medical procedures such as 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...

 (MRI) may be ruled out by the patient having a pacemaker.

In addition, according to the American Heart Association, some home devices have a remote potential to cause interference by occasionally inhibiting a single beat. Cellphones available in the United States (less than 3 watts) do not seem to damage pulse generators or affect how the pacemaker works.

Turning off the pacemaker


According to a consensus statement by the Heart Rhythm Society, it is legal and ethical to honor requests by patients, or by those with legal authority to make decisions for patients, to deactivate implanted cardiac devices. Lawyers say that the legal situation is similar to removing a feeding tube. A patient has a right to refuse or discontinue treatment, including a pacemaker that keeps him or her alive. Physicians have a right to refuse to turn it off, but they should refer the patient to a physician who will. Some patients believe that hopeless, debilitating conditions like strokes, in combination with dementia, can cause so much suffering to themselves and their families that they would prefer not to prolong their lives with supportive measures, such as cardiac devices.

Privacy and security


Security and privacy concerns have been raised with pacemakers that allow wireless communication. Unauthorized third parties may be able to read patient records contained in the pacemaker, or reprogram the devices, as has been demonstrated by a team of researchers. The demonstration worked at short range; they did not attempt to develop a long range antenna. The proof of concept exploit helps demonstrate the need for better security and patient alerting measures in remotely accessible medical implants.

Complications


A possible complication of dual-chamber artificial pacemakers is pacemaker-mediated tachycardia (PMT), a form of reentrant tachycardia. In PMT, the artificial pacemaker forms the anterograde (atrium to ventricle) limb of the circuit and the atrioventricular (AV) node forms the retrograde limb (ventricle to atrium) of the circuit. Treatment of PMT typically involves reprogramming the pacemaker.

Other devices with pacemaker function


Sometimes devices resembling pacemakers, called implantable cardioverter-defibrillator
Implantable cardioverter-defibrillator
An implantable cardioverter-defibrillator is a small battery-powered electrical impulse generator which is implanted in patients who are at risk of sudden cardiac death due to ventricular fibrillation and ventricular tachycardia. The device is programmed to detect cardiac arrhythmia and correct it...

s (ICDs) are implanted. These devices are often used in the treatment of patients at risk from sudden cardiac death. An ICD has the ability to treat many types of heart rhythm disturbances by means of pacing, cardioversion
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...

, or defibrillation
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...

. Some ICD 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.
NASPE / BPEG Defibrillator (NBD) code - 1993
I II III IV
Shock chamber Antitachycardia pacing chamber Tachycardia detection Antibradycardia pacing chamber
O = None O = None E = Electrogram O = None
A = Atrium A = Atrium H = Hemodynamic A = Atrium
V = Ventricle V = Ventricle V = Ventricle
D = Dual (A+V) D = Dual (A+V) D = Dual (A+V)

Short form of the NASPE/BPEG Defibrillator (NBD) code
ICD-S ICD with shock capability only
ICD-B ICD with bradycardia pacing as well as shock
ICD-T ICD with tachycardia (and bradycardia) pacing as well as shock


See also

  • Biological pacemaker
    Biological pacemaker
    The heart is endowed with specialized excitatory and conducting cells that are responsible for the generation and conduction of rhythmic impulses and contractions throughout the heart...

  • Cardiac pacemaker
    Cardiac pacemaker
    right|thumb|350px|Image showing the cardiac pacemaker which is the SA nodeThe contraction of heart muscle in all animals with hearts is initiated by chemical impulses. The rate at which these impulses fire controls the heart rate...

  • Cardiology
    Cardiology
    Cardiology is a medical specialty dealing with disorders of the heart . The field includes diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology...

  • Electrical conduction system of the heart
    Electrical conduction system of the heart
    The normal intrinsic electrical conduction of the heart allows electrical propagation to be transmitted from the Sinoatrial Node through both atria and forward to the Atrioventricular Node. Normal/baseline physiology allows further propagation from the AV node to the ventricle or Purkinje Fibers...

  • Transcutaneous pacing
    Transcutaneous pacing
    Transcutaneous pacing is a temporary means of pacing a patient's heart during a medical emergency. It is accomplished by delivering pulses of electric current through the patient's chest, which stimulates the heart to contract....

  • Pacemaker syndrome
    Pacemaker syndrome
    Pacemaker syndrome is a disease that represents the clinical consequences of suboptimal atrioventricular synchrony or AV dyssynchrony, regardless of the pacing mode, after the pacemaker plantation....

  • Infective endocarditis
    Infective endocarditis
    Infective endocarditis is a form of endocarditis, or inflammation, of the inner tissue of the heart, such as its valves, caused by infectious agents. The agents are usually bacterial, but other organisms can also be responsible....


External links