Pacemakers

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Definition

A pacemaker is a surgically-implanted electronic device that regulates a slow or erratic heartbeat.

Description

Approximately 500,000 Americans have an implantable permanent pacemaker device. A pacemaker implantation is performed under local anesthesia in a hospital by a surgeon assisted by a cardiologist. An insulated wire called a lead is inserted into an incision above the collarbone and guided through a large vein into the chambers of the heart. Depending on the configuration of the pacemaker and the clinical needs of the patient, as many as three leads may be used in a pacing system. Current pacemakers have a double, or bipolar, electrode attached to the end of each lead. The electrodes deliver an electrical charge to the heart to regulate heartbeat. They are positioned on the areas of the heart that require stimulation. The leads are then attached to the pacemaker device, which is implanted under the skin of the patient's chest.

Patients undergoing surgical pacemaker implantation usually stay in the hospital overnight. Once the procedure is complete, the patient's vital signs are monitored and a chest x ray is taken to ensure that the pacemaker and leads are properly positioned.

Modern pacemakers have sophisticated programming capabilities and are extremely compact. The smallest weigh less than 13 grams (under half an ounce) and are the size of two stacked silver dollars. The actual pacing device contains a pulse generator, circuitry programmed to monitor heart rate and deliver stimulation, and a lithiumiodide battery. Battery life typically ranges from seven to 15 years, depending on the number of leads the pacemaker is configured with and how much energy the pacemaker uses. When a new battery is required, the unit can be exchanged in a simple outpatient procedure.

A temporary pacing system is sometimes recommended for patients who are experiencing irregular heartbeats as a result of a recent heart attack or other acute medical condition. The implantation procedure for the pacemaker leads is similar to that for a permanent pacing system, but the actual pacemaker unit housing the pulse generator remains outside the patient's body. Temporary

pacing systems may be replaced with a permanent device at a later date.

— Paula Anne Ford-Martin

Dictionary: pace·mak·er  (pās'mā'kər)

1. Sports. One who sets the pace in a race. Also called pacer, pacesetter.
2. A leader in a field: the fashion house that is the pacemaker. Also called pacesetter.
3. 1. A part of the body, such as the mass of muscle fibers of the sinoatrial node, that sets the pace or rhythm of physiological activity.
   2. Any of several usually miniaturized and surgically implanted electronic devices used to stimulate or regulate contractions of the heart muscle.
4. Biochemistry. A substance that regulates a series of related reactions.

The pacemaker is an electronic biomedical device that can regulate the human heartbeat when its natural regulating mechanisms break down. It is a small box surgically implanted in the chest cavity and has electrodes that are in direct contact with the heart. First developed in the 1950s, the pacemaker has undergone various design changes and has found new applications since its invention. Today, pacemakers are widely used, implanted in tens of thousands of patients annually.

Background

The heart is composed of four chambers, which make up two pumps. The right pump receives the blood returning from the body and pumps it to the lungs. The left pump gets blood from the lungs and pumps it out to the rest of the body. Each pump is made up of two chambers, an atrium and a ventricle. The atrium collects the incoming blood. When it contracts, it transfers the blood to the ventricle. When the ventricle contracts, the blood is pumped away from the heart.

In a normal functioning heart, the pumping action is synchronized by the pacemaker region of the heart, or sinoatrial node, which is located in the right atrium. This is a natural pacemaker that has the ability to create electrical energy. The electrical impulse is created by the diffusion of calcium ions, sodium ions, and potassium ions across the membrane of cells in the pacemaker region. The impulse created by the motion of these ions is first transferred to the atria, causing them to contract and push blood into the ventricles. After about 150 milliseconds, the impulse moves to the ventricles, causing them to contract and pump blood away from the heart. As the impulse moves away from each chamber of the heart, that section relaxes.

Unfortunately, the natural pacemaker can malfunction, leading to abnormal heartbeats. These arrhythmias can be very serious, causing blackouts, heart attacks, and even death. Electronic pacemakers are designed to supplement the heart's own natural controls and to regulate the beating heart when these break down. It is able to do this because it is equipped with sensors that constantly monitor the patient's heart, and a battery that sends electricity, when needed, through lead wires to the heart itself to stimulate the heart to beat.

In addition to outer units, artificial pacemakers can be permanently implanted in a patient's chest. This is done by first guiding the lead through a vein and into a chamber of the heart, where the lead is secured. Fluoroscopic imaging helps facilitate this process. The pacemaker itself is next placed in a pocket, which is formed by surgery just above the upper abdominal quadrant. The lead wire is then connected to the pacemaker, and the pocket is sewn shut. This is a vast improvement over early methods, which required opening the chest cavity and attaching the leads directly to the outer surface of the heart.

History

The idea of using an electronic device to provide consistent regulation of the beating heart was not initially obvious to the early developers of the pacemaker. The first pacemaker, developed by Paul Zoll in 1952, was a portable version of a cardiac resuscitator. It had two lead wires that could be attached to a belt worn by the patient. It was plugged into the nearest wall socket and delivered an electric shock that stimulated the heart of a patient having an attack. This stimulation would usually be enough to cause the heart to resume its normal function. While moderately effective, this early pacemaker was primarily used in emergency situations.

Through 1957 and 1960 significant improvements were made to Zoll's original invention. In an attempt to reduce the amount of voltage needed to restart the heart and increase the length of time electronic pacing could be accomplished, C. Walton Lillehei made a pacemaker that had leads attached directly to the outer wall of the heart. Later, in 1958, a battery was added as the power source, making the pacemaker truly portable, which allowed patients to be mobile. This also enabled patients to use the pacemaker continuously instead of only for emergencies. Lillehei's pacemaker was external. William Chardack and Wilson Greatbatch invented the first implantable pacemaker. It was implanted in a living patient in 1960.

The modern technique for putting a pacemaker into a patient's heart was developed by Seymour Furman. Instead of cutting open the chest cavity, he used a method of inserting the leads into a vein and threading them up into the ventricles. With the leads inside the heart, even lower voltages were needed to regulate the heartbeat. This increased the length of time a pacemaker could be inside a person. Although his method was not widely used initially, by the late 1960s most cardiac specialists had switched to Furman's endocardial pacemakers. Since then improvements have been made in their design, including smaller pacemaker devices, longer lasting batteries, and computer controls.

Raw Materials

The materials used to construct pacemakers must be pharnacologically inert, nontoxic, sterilizable, and able to function in the environmental conditions of the body. The various parts of the pacemaker, including the casing, microelectronics, and the leads, are all made with biocompatible materials. Typically, the casing is made of titanium or a titanium alloy. The lead is also made of a metal alloy, but it is insulated by a polymer such as polyurethane. Only the metal tip of the lead is exposed. The circuitry is usually made of modified silicon semiconductors.

Design

Many types of pacemakers are available. The North American Society of Pacing and Electrophysiology (NASPE) has classified them by which heart chamber is paced, which chamber is sensed, how the pacemaker responds to a sensed beat, and whether it is programmable. Despite this vast array of models, all pacemakers are essentially composed of a battery, lead wires, and circuitry.

The primary function of a pacemaker battery is to store enough energy to stimulate the heart with a jolt of electricity. Additionally, it also provides power to the sensors and timing devices. Since these batteries are implanted into the body, they are designed to meet specific characteristics. First, they must be able to generate about five volts of power, a level that is slightly higher than the amount required to stimulate the heart. Second, they must retain their power over many years. A minimum time frame is four years. Third, they must have a predictable life cycle, allowing the doctor to know when a replacement is required. Finally, they must be able to function when hermetically (airtight) sealed. Batteries have two metals that form the anode and cathode. These are the battery components through which charge is transferred. Some examples include lithium/iodide, cadmium/nickel oxide, and nuclear batteries.

Pacemaker leads are thin, insulated wires that are designed to carry electricity between the battery and the heart. Depending on the type of pacemaker, it will contain either a single lead, for single chamber pacemakers, or two leads, for dual chamber pacemakers. With the constant beating of the heart, these wires are chronically flexed and must be resistant to fracture. There are many styles of leads available, with primary design differences found at the exposed end. Many of the leads have a screw-in tip, which helps anchor them to the inner wall of the heart.

The circuitry is the control center of the pacemaker. Located here are heart monitoring sensors, voltage regulators, timing circuits, and externally programmable controls. The circuitry is composed primarily of resistors, capacitors, diodes, and semiconductors. Modern pacemaker circuitry is a vast improvement over earlier models. With the application of semiconductors, circuit boards have become much smaller. They also require less energy, produce less heat, and are highly reliable.

The Manufacturing
Process

Pacemakers are sophisticated electronic devices. Therefore, some manufacturers rely on outside suppliers to provide many of the component parts. The construction of a pacemaker is not a linear process but an integrated one. Component parts such as the battery, leads, and the circuitry are constructed individually, then pieced together to form the final product.

Making the battery

• The primary type of battery used in pacemakers is a lithium/iodine cell. One method used by manufacturers to make these batteries involves first mixing together the iodine and a polymer such as poly2-vinylpyridine (PVP). They are heated together, forming a molten charge-transfer complex. This liquid is then poured into a half moon-shaped, preformed cell which contains the other components of the battery, including the lithium anode (positive charge) and a cathode collector screen. The iodine/polymer blend solidifies as it cools to form the cathode. After the cathode is formed, the battery is hermetically sealed to prevent moisture from entering.

Making the leads

• The leads are typically composed of a metal alloy. The wire is made by an extrusion process in which the metal is heated until it is molten, then pushed through an appropriately sized opening. It is cut, then bundled with many other wires and treated with a polymeric insulator such as polyurethane. One end of the lead wires is fashioned with a shaped tip, and the other is fitted with a pacemaker connector.

Making the motherboard

• The motherboard contains all the electrical circuitry of the pacemaker, including the semiconductor chips, resistors, capacitors, and other devices. Using a complex method known as hybridization, these components are combined to form a single complex circuit. Construction begins with a small board (less than 0.32 sq in [2 sq cm]) which has the electronic configuration mapped out. The appropriate components are put in place on the board. They are then affixed using a minimum number of soldering welds.

Final assembly and packaging

• When all of the component pieces are available, final assembly takes place. The circuitry is connected to the battery, and both are inserted into the metal casing. The casing used for a pacemaker is typically formed using titanium or a titanium alloy. It is constructed in multiple pieces that are sealed together after the other pacemaker components are introduced. A fitting is also affixed to the casing, providing a connecting point for the leads.
• The finished devices are then put into final packaging along with accessories. After being exhaustively tested, they are then sent out to distributors and finally to doctors.

Quality Control

The quality of each pacemaker is ensured by making visual and electrical inspections throughout the entire production process. These tests will detect most flaws. Since the batteries must be absolutely reliable, they are specially manufactured and exhaustively tested, thereby increasing the associated costs tremendously. The functionality of each finished pacemaker is also tested before it is sent out for sale. Many of these tests are done under varying environmental conditions, such as excessive humidity and stress.

Manufacturers set their own quality standards for the pacemakers that they produce. However, standards and performance recommendations are required by various medical organizations and governmental agencies. In the United States, pacemakers are classified as Class III biomedical devices, which means they require pre-market approval from the United States Food and Drug Administration (FDA).

The Future

With the increasing numbers of senior citizens in the United States, it is anticipated that a greater percentage of the population will require pacemakers. As research efforts continue, future devices promise to be longer lasting, more reliable, and more versatile. Advances in battery technology, such as using radioactive isotopes for power, will undoubtedly improve the longevity of implanted pacemakers. Developments in microelectronics should provide even smaller devices which are less prone to environmental interferences. A late-breaking development in the field is the application of cardiac pacemaking technology to the brain. In this system, scientists connect the lead wires to a specific site on the brain and stimulate it as needed to regulate heartbeat. This device has been shown to be particularly effective in calming the tremors associated with Parkinson's disease.

Where to Learn More

Books

Banbury, Catherine. Surviving Technological Innovation in the Pacemaker Industry, 1959-1990. Garland Pub., 1997.

Ellenbogen, Kenneth, ed. Clinical Cardiac Pacing. Saunders, 1995.

Fox, Stuart. Human Physiology. WCB Publishers, 1990.

Moses, H., J. Schneider, B. Miller, and G. Taylor. A Practical Guide to Cardiac Pacing. Little, Brown and Co., 1991.

Periodicals

Jeffrey, Kirk. "Many Paths to the Pacemaker." Invention & Technology, Spring 1997, pp. 28-39.

[Article by: Perry Romanowski]

In the healthy heart the cells of the sino-atrial (SA) node constitute the natural pacemaker, generating regular electrical signals which spread through the heart and cause it to beat. An artificial pacemaker is required if for any reason, usually heart block, this natural system is compromised, resulting in an irregularly or consistently slow heart rate (bradycardia).

An artificial pacemaker contains a battery and circuitry which produces electrical pulses of short duration capable of stimulating the heart. The device was invented by Wilson Greatbatch of the USA and patented in 1960 after surgeons in New York had made the first clinically successful implant in a 77-year-old man. The pulses are delivered via an electrode which makes direct contact with the heart muscle. Pacemakers can be made to stimulate the heart at a fixed rate irrespective of the intrinsic heart rate, or a demand pacemaker may be used which is capable of sensing the native rhythm and pacing the heart only when the sensed rate falls below a certain value. Recent advances in design have produced pacemakers that are capable of re-synchronizing atrial and ventricular activity, thus functioning as a defibrillator.

A temporary pacemaker can be fitted by placing the pacing electrode within the right ventricle. The electrode is introduced through a needle inserted into a large vein in an arm or the neck. The electrode is advanced, under X-ray monitoring, within the vein following its course back to the heart. Once the electrode is in contact with the inner surface of the heart it is connected to the pacemaker, which remains outside the body. A temporary pacemaker may be required in the short term for certain individuals after a heart attack, during cardiac surgery or general anaesthesia. A permanent pacemaker is fitted in people requiring long-term pacing. The electrode in a permanent pacemaker is also introduced into a vein, but the vein in this case is surgically exposed. The permanent pacemaker is sufficiently small to be placed in a small pouch formed within the muscle under the skin; it is con-nected to the pacing electrode. Less commonly, pacemakers may be implanted that can detect the onset of abnormal tachycardias (fast heart rate). The pacemaker can stimulate the heart in competition with the abnormal beat in an attempt to return it to a normal rhythm. More recently, power supplies capable of delivering high energies for defibrillation have been introduced. The pacemaker may last five to fifteen years, depending on the lifetime of the battery and the frequency of stimulation. More modern versions can retain a microchip memory of their activity for periods of up to a year; this information can then be routinely ‘downloaded’ for analysis so that the physician has access to a detailed electrical history of the patient's heart. Pacemaker batteries can usually be recharged via an induction coil outside the skin so no further surgery is required. Modern pacemakers thus have increasingly sophisticated microprocessor-controlled ‘brains’. Like all such equipment, there is a risk of electrical interference by very powerful electrical devices; these risks are often signposted.

— David J. Miller, Niall G. MacFarlane

See also defibrillator; heart; heart block.

An electrical device used to maintain a normal sinus rhythm in heart muscle contraction. Pacemakers can be permanent indwelling appliances. The use of electronic devices on patients with pacemakers is now considered permissible because of modern shields. Also called cardiac pacemaker.

For more information on pacemaker, visit Britannica.com.

1. A small region of cardiac tissue in the right atrium of the heart (see sinoatrial node), which controls the rate of contraction of the heart as a whole,

2. A device that controls the heart rate of a patient who has heart block.

A group of specialized muscle fibers in the heart that send out impulses to regulate the heartbeat. If the heart's built-in pacemaker does not function properly, an artificial pacemaker may be necessary — a small electrical device that also regulates the heartbeat by sending out impulses. An artificial pacemaker may be placed inside the body surgically or may be worn outside.

1. an object or substance that controls the rate at which a certain phenomenon occurs; often used alone to indicate an artificial cardiac pacemaker; however, there are other natural and artificial pacemakers.
2. In biochemistry, a pacemaker is a substance whose rate of reaction sets the pace for a series of interrelated reactions.

• asynchronous p. — (1) an implanted cardiac pacemaker in which the induced ventricular rhythm is independent of the atrium; it is usually set at a fixed rate of ventricular stimulation.
• p. cells — (1) cells within the heart capable of spontaneous discharge.
• gastric p. — (1) a saddle-shaped area of the greater curvature of the stomach at the junction of its proximal and middle thirds, which regulates the frequency of gastric contractions.
• phrenic p. — (1) a device designed to facilitate respiration by converting radiofrequency signals into electrical impulses that stimulate the phrenic nerve, resulting in contraction and flattening of the diaphragm and improved inspiration of air.
• p. therapy — implantation of a pacemaker device in animals usually for the treatment of symptomatic bradyarrhythmias.
• p. syndrome — falling arterial pressure, low cardiac output and congestive heart failure, usually due to a suboptimal pacing mode.
• uterine p. — either of the two regulating centers that control uterine contractions.
• wandering p. — a condition in which the site of origin of the impulses controlling the heart rate shifts from the head of the sinoatrial node to a lower part of the node or to another part of the atrium.

A pacemaker, scale in centimeters

A pacemaker (or artificial pacemaker, so as not to be confused with the heart's natural pacemaker) is a medical device which uses electrical impulses, delivered by electrodes contacting the heart muscles, to regulate the beating of the heart. The primary purpose of a pacemaker is to maintain an adequate heart rate, either because the heart's native pacemaker is not fast enough, or there is a block in the heart's electrical conduction system. Modern pacemakers are externally programmable and allow the cardiologist to select the optimum pacing modes for individual patients. Some combine a pacemaker and implantable defibrillator in a single implantable device. Others have multiple electrodes stimulating differing positions within the heart to improve synchronisation of the lower chambers of the heart.

History of the artificial pacemaker

In 1889 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 caused a ventricular 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.^[1]

In 1928 Dr Mark C Lidwell of the Royal Prince Alfred Hospital of Sydney, supported by physicist Edgar H Booth of the University of Sydney, 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" The apparatus was used to revive a stillborn infant at Crown Street Women's Hospital, Sydney whose heart continued "to beat on its own accord", "at the end of 10 minutes" of stimulation.^[2][3]

In 1932 American physiologist Albert Hyman, 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.^[4][5]

An apparent hiatus in publication of research conducted between the early 1930s and World War II 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".^[3]

An external pacemaker was designed and built by the Canadian electrical engineer John Hopps in 1950 based upon observations by cardio-thoracic surgeon Wilfred Gordon Bigelow at Toronto General Hospital . A substantial external device using vacuum tube technology to provide transcutaneous pacing, 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 of the patient by inducing ventricular fibrillation.

A number of innovators, including Paul Zoll, made smaller but still bulky transcutaneous pacing devices in the following years using a large rechargeable battery as the power supply.^[6]

In 1957 Dr. William L. Weirich published the results of research performed at the University of Minnesota. These studies demonstrated the restoration of heart rate, cardiac output and mean aortic pressures in animal subjects with complete heart block through the use of a myocardial electrode. This effective control of postsurgical heart block proved to be a significant contribution to decreasing mortality of open heart surgery in this time period.^[7]

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

In 1957 engineer Earl Bakken of Minneapolis, Minnesota, produced the first wearable external pacemaker for a patient of Dr. C. Walton Lillehei. 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 University Hospital in Solna, Sweden, using a pacemaker designed by Rune Elmqvist and surgeon Åke Senning, connected to electrodes attached to the myocardium of the heart by thoracotomy . 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, survived the first tests and died in 2001 after having received 22 different pacemakers during his lifetime.

In 1959 temporary transvenous pacing was first demonstrated by Furman et al in which the catheter electrode was inserted via the patient's basilic vein.^[8]

In February,1960, an improved version of the Swedish Elmqvist design was implanted in Montevideo, Uruguay 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 entered use in humans from April 1960 following extensive animal testing. The Greatbatch innovation varied from the earlier Swedish devices in using primary cells (mercury battery) as the energy source. The first patient lived for a further 18 months.

The first use of transvenous pacing in conjunction with an implanted pacemaker was by Parsonnet in the USA ^[9][10], Lageren in Sweden^[11][12] and Jean-Jaques Welti in France^[13] in 1962-63. The transvenous, or pervenous, procedure involved incision of a vein into which was inserted the catheter 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. In the late 1960s several companies, including ARCO in the USA, developed isotope powered pacemakers, but this development was overtaken by the development in 1970 of the lithium-iodide cell by Wilson Greatbatch. 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 resin encapsulation affecting the electronic circuitry. This phenomenon was overcome by encasing the pacemaker generator in an hermetically sealed metal case, initially by Telectronics 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 Minneapolis, J.G (Geoffrey) Davies of St George's Hospital London, Barouh Berkovits and Sheldon Thaler of American Optical, Geoffrey Wickham of Telectronics Australia, Walter Keller of Cordis Corp. of Miami, Hans Thornander who joined previously mentioned Rune Elmquist of Elema-Schonander in Sweden, Janwillem van den Berg of Holland and Anthony Adducci of Cardiac Pacemakers Inc.(Guidant)

Applications

Artificial pacemakers can be used in order to help with and/or treat these conditions:

• Sinus node dysfunction - when the sinoatrial node does not fire properly to contract the heart
• Bifascicular block, trifascicular block, or third degree AV block.
• Stokes-Adams attack involving disruption of conduction between the sinoatrial node and the atrioventricular node.

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, 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 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.^[14]

Transcutaneous pacing

Main article: Transcutaneous pacing

Transcutaneous pacing (TCP), also called external pacing, is recommended for the initial stabilization of hemodynamically significant bradycardias 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) is achieved, with a corresponding pulse. Pacing artifact on the ECG 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.

Transvenous pacing (temporary)

Main article: Transvenous pacing

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

An artificial pacemaker with electrode for transvenous insertion (from St. Jude Medical). The body of the device is about 4 centimeters long, the electrode measures between 50 and 60 centimeters.

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 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.

The pacemaker generator is an hermetically sealed device containing a power source, usually a lithium battery, a sensing amplifier which processes the electrical manifestation of naturally occuring heart beats as sensed by the heart electrodes, the computer 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. It is usually made of titanium, which is inert in the body.

Basic pacemaker function

Modern pacemakers usually have multiple functions. The most basic form monitors the heart's native electrical rhythm. When the pacemaker doesn't 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^[15]

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)

Biventricular Pacing (BVP)

A biventricular pacemaker, also known as CRT (cardiac resynchronization therapy) is a type of pacemaker that can pace both ventricles (right and left) of the heart. By pacing both sides of the heart, the pacemaker can resynchronize a heart that does not beat in synchrony, which is common in heart failure patients. CRT devices have three leads, one in the atrium, one in the right ventricle, and a final one is inserted through the coronary sinus to pace the left ventricle. CRT devices are shown to reduce mortality and improve quality of life in groups of heart failure patients.^[16][17][18]. CRT can be combined with an implantable cardioverter-defibrillator (ICD) ^[19].

Advancements in pacemaker function

When first invented, pacemakers controlled only the rate at which the heart's two largest chambers, the ventricles, beat.

Many advancements have been made to enhance the control of the pacemaker once implanted. Many of these enhancements 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^[20] have shown that unnecessary pacing of the right ventricle can lead to heart failure. The newer bi-ventricular devices can keep the amount of right ventricle pacing to a minimum and thus prevent worsening of the heart disease.

Other devices with pacemaker function

Main article: Implantable cardioverter-defibrillator

Sometimes devices resembling pacemakers, called ICDs (implantable cardioverter-defibrillators) 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, or defibrillation.

NASPE / BPEG Defibrillator (NBD) code - 1993^[21]

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^[21]

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

• Cardiology
• Electrical conduction system of the heart
• Transcutaneous pacing

References

1. ^ "Electrical Stimulation of the Heart in Man - 1889", Heart Rhythm Society, Accessed May 11, 2007
2. ^ Lidwell M C, "Cardiac Disease in Relation to Anaesthesia" in Transactions of the Third Session, Australasian Medical Congress, Sydney, Australia, Sept. 2-7 1929, p 160.
3. ^ ^{a b} Mond H, Sloman J, Edwards R (1982). "The first pacemaker". Pacing and clinical electrophysiology : PACE 5 (2): 278-82. PMID 6176970. 
4. ^ Aquilina O, "A brief history of cardiac pacing", Images Paediatr Cardiol 27 (2006), pp.17-81.
5. ^ Furman S, Szarka G, Layvand D, "Reconstruction of Hyman's second pacemaker", Pacing Clin Electrophysiol.2005 May;28(5):446-453
6. ^ http://www.hno.harvard.edu/gazette/2001/04.19/12-zoll.html
7. ^ Weirich W, Gott V, Lillehei C: The treatment of complete heart block by the combined use of a myocardial electrode and an artificial pacemaker. Surg. Forum 1957;8;360-363
8. ^ "Furman S, Schwedel JB" An intracardiac pacemaker for Stokes-Adams Seizures N Eng J Med 1959; 261:943-948"
9. ^ "Permanent Transvenous Pacing in 1962", Parsonnet V, PACE,1:285, 1978
10. ^ "Preliminary Investigation of the Development of a Permanent Implantable Pacemaker Using an Intracardiac Dipolar Electrode", Parsonnet V, Zucker I R, Asa M M, Clin. Res., 10:391, 1962
11. ^ "How It Happened: My Recollection of Early Pacing", Lageren H, PACE: Pacing and Clinical Electrophysiology 1.1, Jan. 1978, pp 140-143
12. ^ "Intracardiac Stimulation for Complete Heart Block", Lageren H, Acta. Chir. Sca., 125:562, 1963
13. ^ Jean Jaques Welti:Biography, Heart Rhythm Foundation
14. ^ (Cite_Journal)Percussion pacing in a three year-old girl with complete heart block during cardiac catheterization. C Eich, A Bleckmann and T. Paul, retrieved from http://bja.oxfordjournals.org/cgi/content/full/95/4/465
15. ^ Bernstein A, Daubert J, Fletcher R, Hayes D, Lüderitz B, Reynolds D, Schoenfeld M, Sutton R (2002). "The revised NASPE/BPEG generic code for antibradycardia, adaptive-rate, and multisite pacing. North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group". Pacing Clin Electrophysiol 25 (2): 260-4. PMID 11916002. 
16. ^ Cleland JGF, Daubert J-C, Erdmann E, et al; the Cardiac Resynchronization — Heart Failure (CARE-HF) Study Investigators. The effect of cardiac resynchronization on morbidity and mortality in heart failure. N Engl J Med. 2005 March 7 Fulltext. PMID 15753115.
17. ^ Bardy GH, Lee KL, Mark DB, et al for the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) Investigators. Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure. N Engl J Med 2005; 352:225–237
18. ^ Cleland J, Daubert J, Erdmann E, Freemantle N, Gras D, Kappenberger L, Tavazzi L (2005). "The effect of cardiac resynchronization on morbidity and mortality in heart failure". N Engl J Med 352 (15): 1539-49. PMID 15753115. 
19. ^ Bristow M, Saxon L, Boehmer J, Krueger S, Kass D, De Marco T, Carson P, DiCarlo L, DeMets D, White B, DeVries D, Feldman A (2004). "Cardiac-resynchronization therapy with or without an implantable defibrillator in advanced chronic heart failure". N Engl J Med 350 (21): 2140-50. PMID 15152059. 
20. ^ Wilkoff BL, Cook JR, Epstein AE, et al.: Dual-chamber pacing or ventricular backup pacing in patients with an implantable defibrillator: the Dual-chamber and VVI Implantable Defibrillator (DAVID) Trial. JAMA 2002, 288: 3115–3123. [1]
21. ^ ^{a b} Bernstein A, Camm A, Fisher J, Fletcher R, Mead R, Nathan A, Parsonnet V, Rickards A, Smyth N, Sutton R (1993). "North American Society of Pacing and Electrophysiology policy statement. The NASPE/BPEG defibrillator code". Pacing Clin Electrophysiol 16 (9): 1776-80. PMID 7692407. 

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Dansk (Danish)
n. - pacemaker, pacer

Nederlands (Dutch)
pacemaker, iemand die tempo van wedstrijd bepaalt, koploper

Français (French)
n. - (Méd) stimulateur cardiaque, (Sport) lièvre, meneur de train

Deutsch (German)
n. - Schrittmacher

Ελληνική (Greek)
n. - πρωτοπόρος που δίνει το ρυθμό της κούρσας, (ιατρ.) (καρδιακός) βηματοδότης

Italiano (Italian)
stimolatore cardiaco

Português (Portuguese)
n. - marca-passo (m)

Русский (Russian)
стимулятор работы сердца

Español (Spanish)
n. - marcapasos

Svenska (Swedish)
n. - farthållare (sport), pacemaker, hare, pacemaker (med.), hjärtstimulator, batterihjärta

中文（简体） (Chinese (Simplified))
领跑者, 标兵, 带头人

中文（繁體） (Chinese (Traditional))
n. - 領跑者, 標兵, 帶頭人

한국어 (Korean)
n. - 보조 조정자, 선도자, 맥박조정기

日本語 (Japanese)
n. - ペースメーカー, 脈拍調整器, 先導者

العربيه (Arabic)
‏(الاسم) منظم للخطوات, محدد الخطوة أو سرعه الانطلاق, فارس, , عداء, يحدد سرعه الانطلاق‏

עברית (Hebrew)
n. - ‮קוצב לב, קובע קצב‬

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