AskDefine | Define pacemaker

Dictionary Definition

pacemaker

Noun

1 a leading instance in its field; "the new policy will be a pacesetter in community relations" [syn: pacesetter]
2 a specialized bit of heart tissue that controls the heartbeat [syn: cardiac pacemaker, sinoatrial node, SA node]
3 an implanted electronic device that takes over the function of the natural cardiac pacemaker [syn: artificial pacemaker]
4 a horse used to set the pace in racing [syn: pacer, pacesetter]

User Contributed Dictionary

English

Etymology

pace + maker

Noun

  1. One who sets the pace in a race, to guide the others.
  2. A set of nerves which stimulate the heart to beat.
  3. In the context of "hence": A medical implement that is used to stimulate a heart to beat by simulating the action of the natural pacemaker.

Translations

One who sets the pace in a race.
medical implement

Extensive Definition

''For other uses see Pacemaker (disambiguation)
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.
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.
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.
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".
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.
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, went on to receive 26 different pacemakers during his lifetime. He died in 2001, at the age of 86.
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.
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 , Lageren 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 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.
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 occurring 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.

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.. CRT can be combined with an implantable cardioverter-defibrillator (ICD) .

Advancements in pacemaker function

One unrealized advancement in pacemaker function could mimic nature by utilizing various bodily input parameters such as CO2 - O2 at in arterial-vein system, body temperature, ATP levels, Adrenaline, etc. Instead of producing a static, predetermined heart rate, or intermittent control, a Dynamic Pacemaker could compensate for both actual respiratory loading and potentially anticipated respiratory loading. A Dynamic Pacemaker would require sensory technology for which heart-rate regulation parameters must first be acutely identified. 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.
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 have shown that unnecessary pacing of the right ventricle can lead to heart failure and an increased 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.

Pacemaker Patient Considerations

Pacemaker Insertion

A pacemaker is typically inserted into the patient through a simple surgery using a local anesthetic. The patient is usually given a drug for relaxation. An incision is made in the left shoulder area below the collar bone 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. A temporary drain may be installed and removed the following day. The actual surgery may take about an hour.
The patient should exercise reasonable care about the wound as it heals.
Following surgery there is a followup session during which the pacemaker is checked using a portable device that can communicate with the pacemaker and allows a technician to determine the settings such as pacing threshold.

Pacemaker Patient Identification Card

International Pacemaker Patient Identification Cards patient data (between others, sympton primary, ECG, aetiology), pacemaker center (doctor, hospital), IPG (rate, mode, date of implantation, MFG, type) and lead .

Living With a Pacemaker

Periodic Pacemaker Checkups

Once the pacemaker is inserted and functional, it is periodically checked to ensure the device is operational and is performing well. Typically, a long distance check is performed via telephone every three months and a more thorough check is made once a year. At the time of the more thorough checkup, a device is used that will communicate with the pacemaker in order to read operational statistics kept by the device as well as to read its current status such as estimated battery life.
Battery life of the pacemaker will vary depending on how often the device is actually pacing the heart. Typically battery life is estimated at eight years though it may vary in a range of five to ten years. One of the purposes of the periodic pacemaker check is to monitor battery reserves and to estimate battery life remaining.

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 or maintaining heavy equipment that may generate intense magnetic fields.
Some medical procedures may require the use of antibiotics to be administered before the procedure. The patient should inform all medical personnel that the patient does have a pacemaker. Some standard medical procedures such as the use of Magnetic resonance imaging or MRI may be ruled out by the patient having a pacemaker.

Other devices with pacemaker function

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.

References

pacemaker in Danish: Kunstig pacemaker
pacemaker in German: Herzschrittmacher
pacemaker in Spanish: Marcapasos
pacemaker in French: Stimulateur cardiaque
pacemaker in Italian: Pacemaker
pacemaker in Hebrew: קוצב לב
pacemaker in Dutch: Pacemaker
pacemaker in Japanese: 心臓ペースメーカー
pacemaker in Norwegian: Pacemaker
pacemaker in Norwegian Nynorsk: Pacemaker
pacemaker in Polish: Stała elektrostymulacja serca
pacemaker in Portuguese: Marcapasso
pacemaker in Russian: Электрокардиостимулятор
pacemaker in Slovak: Kardiostimulátor
pacemaker in Finnish: Sydämentahdistin
pacemaker in Swedish: Pacemaker
pacemaker in Turkish: Kalp pili
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