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A pacemaker (or "artificial pacemaker", so as not to be confused with the heart's natural pacemaker) is a medical device designed to regulate the beating of the heart. The purpose of an artificial pacemaker is to stimulate the heart when either the heart's native pacemaker is not fast enough or if there are blocks in the heart's electrical conduction system preventing the propagation of electrical impulses from the native pacemaker to the lower chambers of the heart, known as the ventricles. Generally, pacemakers do not treat fast rhythms of the heart.
History of the implantable pacemaker
The first external pacemaker was designed and built by the Canadian electrical engineer John Hopps in 1950. A substantial external device, it was somewhat crude and painful to the patient in use. A number of inventors, including Paul Zoll, made smaller but still bulky external devices in the following years. The pacemakers built in the late 1950s were bulky, relied on external electrodes, and had to be plugged into a wall outlet. External electric shocks were frequently too traumatic for young heart block patients, and the AC-operated pacemaker could fail during a power blackout.
Dr. C. Walton Lillehei, a pioneer in open heart surgery at the University of Minnesota Medical School and his colleagues set out to develop a better system, and Earl Bakken became closely involved in their work. When a power failure occurred in the Twin Cities and resulted in the death of one of Dr. Lillehei's young patients, the surgeon turned to Earl and for a battery back-up for the AC pacemakers.
Over the next few weeks, Earl developed a new kind of pacemaker that was not much larger than a paperback book. He borrowed parts from other electrical devices that he had in the shop. For the new device's circuitry, he relied on a design for a transistorized metronome he had seen in a trade publication. When finished, he had produced a pacemaker that was powered by mercury batteries, provided a 9-volt DC pulse, and could easily and comfortably be "worn" by young patients.
The original Bakken pacemaker was tested in the University of Minnesota's laboratory. The following day, it was applied to a pediatric heart block patient. The effect was instantaneous. The pacemaker immediately restored the child's heartbeat to near normal. Within days, the child's heart resumed a normal rhythm on its own, and the pacemaker was removed.
The development of the wearable, external, battery-powered pacemaker amounted to a leap forward in the treatment of heart block and other cardiac problems. It also signaled the beginning of a new era in the therapeutic application of electrical technology for patients around the world.
The first implantation into a human was made in 1958 by a Swedish team using a pacemaker designed by Rune Elmqvist and Åke Senning. The device failed after three hours. A second device was then implanted which lasted for two days. The worlds first implantable pacemaker patient, Arne Larsson, survived the first tests and died in 2001 after having received 22 different pacemakers during his lifetime. In February 1960, an improved model relying on better materials was implanted in Montevideo, Uruguay. 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.
Devices constructed by the American Wilson Greatbatch entered use in humans from April 1960 following extensive animal testing. The first patient lived for a further 18 months. The early devices suffered from battery problems - every patient required an additional operation every 24 months to replace the batteries.
Pacemakers require wires (called leads) to both send the pacing pulses to the heart and sense the intrinsic rhythm of the heart. The first pacemakers required these leads to be placed surgically on the outer surface of the heart. In the mid 1960s, the first transvenous leads were placed. This allowed the placement of pacemakers without opening the thoracic cavity and therefore without the use of general anaesthesia.
The first American-made nuclear-powered pacemaker was developed and implanted at Newark Beth Israel Medical Center in Newark, New Jersey.
Indications for pacing
In most cases, the indication for permanent pacemaker placement is a slow heart rate (bradycardia) or a defect in the electrical conduction system of the heart (heart block) with associated symptoms. Typical symptoms of a slow heart rate include lightheadedness, poor exercise tolerance, and loss of consciousness. Individuals who have a slow heart rate but who are asymptomatic do not require a pacemaker. For instance, athletes typically have rest heart rates in the 40s without any deleterious effects.
If the slow heart rate is due to complete heart block, a pacemaker is indicated, since the heart rate can dramatically decrease without notice. Pacemakers can also be placed in patients at high risk for complete heart block.
Rarely, in people prone to ventricular fibrillation, a slow rhythm in the heart can lead to a ventricular fibrillation. In these people, preventing the slow rhythm can prevent ventricular fibrillation.
Methods of pacing
External pacemakers can be used for initial stabilization of a patient, but implantation of a permanent internal pacemaker is usually required for most conditions. External cardiac pacing is typically performed by placing two pacing pads on the chest wall. Usually one pad is placed on the upper portion of the sternum, while the other is placed along the left axilla, near the bottom of the rib cage. When an electrical impulse goes from one pad to the other, it will travel through the tissues between them and stimulate the muscles between them, including the cardiac muscle and the muscles of the chest wall. Electrically stimulating any muscle, including the heart muscle, will make it contract. The stimulation of the muscles of the chest wall will frequently make those muscles twitch at the same rate as the pacemaker is set.
Pacing the heart via external pacing pads should not be relied upon for an extended period of time. If the person is conscious, he or she may feel discomfort due to the frequent stimulation of the muscles of the chest wall. Also, stimulation of the chest wall muscles does not necessarily mean that the heart is being stimulated as well.
Temporary internal pacing
An alternative to external pacing is the temporary internal pacing wire. This is a wire that is placed under sterile conditions via a central line. The distal tip of the wire is placed into either the right atrium or right ventricle. The proximal tip of the wire is attached to the pacemaker generator, outside of the body. Temporary internal pacing is often used as a bridge to permanent pacemaker placement. Under certain conditions, a person may require temporary pacing but would not require permanent pacing. In this case, a temporary pacing wire may be the optimal treatment option.
Permanent pacemaker placement
Placement of a permanent pacemaker involves placement of one or more pacing wires within the chambers of the heart. One end of each wire is attached to the muscle of the heart. The other end is screwed into the pacemaker generator. The pacemaker generator is a hermetically sealed device containing a power source and the computer logic for the pacemaker.
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.
Basic pacemaker function
Modern pacemakers all have two functions. They listen to the heart's native electrical rhythm, and if the device doesn't sense any electrical activity within a certain time period, the device will stimulate the heart with a set amount of energy, measured in joules.
Pacemaker naming code
The NASPE/BPEG generic (NPG) code is a pacemaker naming convention originally developed in 1974 that uses a 3-5 letter code to describe the main features of an artificial pacemaker. Each of the 5 positions signifies a particular aspects of pacemaker functionality. Using this scheme, a designation of VATOO would describe, for example, a pacemaker that sensed the atria and paced the ventricles in a triggered mode with no rate response or multisite pacing.
||Response to Sensing
||O = none, A = atrium, V = ventricle and D = dual (A + V)
||O = none, A = atrium, V = ventricle and D = dual (A + V)
||O = none, T = triggered, I = inhibited and D = dual (T + I)
||O = none, R = rate modulation
||O = none, A = atrium, V = ventricle and D = dual (A + V)
|Manufacturer's designation only
||S = single (A or V)
||S = single (A or V)
Table I. The Revised NASPE/BPEG Generic Code for Antibradycardia Pacing
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 which control not only the ventricles but the atria as well have become common. 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 the sense the physical activity of the patient and respond appropriately by increasing or decreasing the base pacing rate via rate response algorithms.
Another advancement in pacemaker technology is left ventricular pacing. A pacemaker wire is placed on the outer surface of the left ventricle, with the goal of more physiological pacing than what is available in standard pacemakers. This extra wire is implanted to improve symptoms in patients with severe heart failure.
Devices with pacemaker function
Sometimes devices resembling pacemakers, called ICDs (implantable cardioverter-defibrillators) are implanted. These devices have the ability to treat dangerously fast rhythm disturbances of the heart, either via pacing or defibrillation. Many of these can also treat slow heart rhythms the same way as pacemakers.
Individuals who have a pacemaker or ICD implanted are told to avoid strong electromagnetic fields. This includes arc welding machines, MRI machines, lithotripsy, and induction stoves. All these devices can cause pacemaker inhibition due to artificial noise sensed by the pacemaker. High magnetic fields can also (in some cases) directly effect the pacemaker wires, causing dislodgement from the myocardium. Many pacemaker are also controlled by an external magnet, and this sensor might get triggered by an external magnet.
Normally functioning electrical power tools and home appliances are generally considered safe. For more information see the manufacturers' webpages.
What Is a Pacemaker?
A pacemaker system is a two-part electrical system that includes a pulse generator (pacemaker) and one or two leads, or wires, which deliver impulses to the heart. The leads also carry signals back from the heart. By "reading" these signals, the pulse generator is able to monitor the heart?s activity and respond appropriately. A pacemaker helps to pace the heart when the natural rate is too slow (bradycardia) to pump enough blood to the body.
Why Would I Need a Pacemaker?
Your heart is normally regulated by the heart?s natural pacemaker. This natural pacemaker is called the SA (sino-atrial) node. The SA node automatically increases your heart rate in response to your body?s needs -- for example, during exercise, when a faster heart rate is required. Sometimes, the SA node stops working properly. It may improperly speed up or slow down the rate at which it sends out electrical signals. If the signal rate is too slow, the chambers of the heart do not contract often enough to supply the proper amount of blood to your body.
What Is Heart Block?
Problems may also occur with the electrical pathway between the upper heart and the lower heart. The natural pacemaker signals sent out by the SA node may be delayed in the AV (atrioventricular node) or may fail all together. This condition is called "heart block." Heart block often means that the ventricles pump too slowly even though the SA node may be sending out faster signals in an effort to increase the heart rate.
What Is a Pacemaker System?
Your pacemaker alters your heart rate to help meet your body?s needs. It does this by providing pacing signals that are much like the heart?s normal signals. Depending on your particular situation, your pacemaker may:
* Replace the function of the heart?s natural pacemaker or SA node.
* Help maintain a normal timing sequence between the upper and lower heart.
* Make sure critical lower chambers of the heart always contract at an adequate rate.
What Makes Up a Pacemaker?
A pacemaker is roughly the size of a silver dollar and about as thick as 2 silver dollars together. The pacemaker system is powered by a small battery sealed inside the pulse generator. The battery cannot be recharged. For this reason, the pulse generator must be replaced when the battery?s energy is used up. The pacemaker also includes several electronic circuits. These circuits control the pacemaker?s functions, including the way it monitors your heart?s activity. Replacement of the device usually occurs in 4-8 years.
There are two basic kinds of pacemakers: single-chamber and dual-chamber. A single-chamber pacemaker has one lead to carry signals to and from one chamber of your heart --either the right atrium or the right ventricle. A dual-chamber pacemaker has two leads, with the tip of one lead positioned in the right atrium and the tip of the other lead located in the right ventricle.
How Is a Pacemaker Implanted?
The lead(s) are positioned in the right ventricle and also in the right atrium (when needed). A pocket is formed under the skin of the upper chest. The pacemaker is then connected to its leads. Most pacemaker surgery is done under local anesthesia. Additional medicine may be given in an IV to help the patient relax. The procedure typically takes 1 to 1 ? hours.
What Are the Complications?
All surgical procedures contain risks. These should be discussed with a physician.
What Happens After a Pacemaker Is Implanted?
Once the pacemaker is implanted, it is important that the patient be followed by a pacemaker clinic or a commercial group that specializes in pacemaker follow-up. The physician implanting the pacemaker should help the patient arrange appropriate follow-up. Pacemaker follow-up is usually done on a defined schedule. The schedule may vary depending on who is in charge of following or checking the pacemaker. Some physicians will prefer that the patient be seen in the office on a regular basis to have the pacemaker checked. Others will arrange a pacemaker check to be done by telephone, called transtelephonic monitoring, with periodic visits in the office or clinic. In many offices, the pacemaker check will be performed by a nurse or technician that is specially trained in management of pacemakers.
Pacemakers are checked with a special device called a programmer. A portion of the programmer is simply held over the pacemaker and is able to communicate with the pacemaker. It can obtain information about the function of the pacemaker. It can also change certain functions of the pacemaker to whatever the doctor, nurse, or technician feels is most appropriate. A special magnet may also be used during the pacemaker evaluation, and if transtelephonic monitoring is part of the follow-up, a magnet will probably be given to the patient to use during the telephone evaluations.
Frequently Asked Questions
1. How is the battery replaced in the pacemaker?
The battery is sealed inside the pacemaker case, or can, which also contains the electronic circuitry. When the battery?s energy is depleted, a new pacemaker must be implanted. The surgery needed to remove the old pacemaker and implant the new one may require only a local anesthetic and is generally a very brief operation. In most cases, your original pacemaker lead(s) will not need to be replaced.
2. Is there a chance that my pacemaker will fail?
Yes, there is a remote possibility that any electronic device can fail, but technical advances in recent years have made it possible to make pacemakers very reliable.
3. What happens if my pacemaker does fail?
If your pacemaker should fail to function properly, you may experience the same symptoms that you had before you received the pacemaker. If you ever have these symptoms, contact you doctor as soon as possible.
4. Can I use my cellular phone?
Yes. In certain cases, a cellular phone could affect your pacemaker?s operation if it is closer than six inches. This interaction is temporary, and moving the phone away from the pacemaker will return it to proper function. To reduce the chance of interaction, maintain a distance of at least six inches between the cellular phone and your pacemaker; hold the cellular phone on the opposite side of your body from your pacemaker; do not carry a cellular phone in a breast pocket or on a belt if that places the phone within 6 inches of your pacemaker.
5. Will microwave ovens interfere with my pacemaker?
Microwave ovens will not interfere with pacemakers that are manufactured today or in recent years. Patients with pacemakers may use microwaves without concern.
6. Is there other electronic equipment that will interfere with my pacemaker?
Certain types of welding equipment could interfere with a pacemaker and should be discussed with your physician prior to using. There are other industrial sources of potential interference. If you work in an environment where heavy equipment is used, it is worthwhile discussing it with your physician to be certain there is no concern.
Certain types of hospital equipment may cause interference. MRI or magnetic resonance imaging equipment is capable of interference and is generally not performed in patients with pacemakers. MRI has been done in special circumstances in patients with pacemakers. If an MRI was felt to be critical, this would require discussion between you and the doctor ordering the MRI.
External links and References
- Medtronic http://www.medtronic.com
- Biotronik http://www.biotronik.com/content/list.php?page=en_sitemap
- Pacesetter/Telectronics/St.Jude http://www.sjm.com/devices/deviceindex.aspx
- CPI/Guidant http://www.guidant.com/products/pacing.shtml
- ELA Medical http://www.elamedical.com/brady.htm
- Vitatron http://www.vitatron.com
- Medico http://www.medicoweb.com/
- NeuroCor http://www.neurocor.es/
- Sorin http://www.sorinpacing.com/hp10_eng.htm
- More Pacing Links http://internist.at/pacemakere.htm
- Heart Rhythm Society http://hrsonline.org
- Berstein, A. D., Daubert, J., Fletcher, R. D., Hayes, D. L., Luderitz, B., Reynolds, R. D., Schoenfeld and M. H., Sutton, R.: The Revised NASPE/BPEG Generic Code for Antibradycardia, Adaptive-Rate, and Multisite Pacing. Journal of Pacing and Clinical Electrophysiology, Volume 25, No. 2 (2002).  http://www.naspe.org/pdf_files/RevisedNASPE_BPEGGeneric.pdf
Last updated: 02-12-2005 08:26:59
Last updated: 05-03-2005 02:30:17