An artificial pacemaker provides an electrical impulse (or “discharge”) that can stimulate the heart, thus restoring or maintaining a regular heartbeat. Although various types of artificial pacemaker devices are available, they generally include the following components:
A thin metal box or case called a pulse generator (figure 1), which contains the power source producing the electrical impulses of the pacemaker. In addition, the pulse generator contains a small computer processor that can be programmed to set the rate of the pacemaker, the pattern of pacing, the energy output, and various other parameters. The pulse generator for most modern permanent pacemakers weighs one to two ounces.
Flexible insulated wires or leads carry electrical impulses from the generator to the heart muscle and relay information concerning the heart’s natural activities back to the pacemaker. There may be several such wires, or leads, placed within the heart, most commonly in the right atrium and right ventricle.
The pacing lead most commonly incorporates one or two electrical “poles.” An electrical impulse is transmitted to the heart muscle when needed, and the lead is also able to sense the heart’s intrinsic electrical activity.
Types of pacemakers — A variety of types of pacemakers and modes of pacing have been developed to restore or sustain a regular heartbeat in different ways. All contemporary pacemakers sense the intrinsic activity and stimulate the heart only when the intrinsic heart rate falls below the programmed pacing rate. Essentially all contemporary pacemakers also incorporate rate responsive capability. This depends on a “sensor” incorporated into the pacemaker that can sense activity or respiratory rate and can alter the heart rate based on the perceived physiologic need.
Pacemakers may also be single, dual, or triple chambered:
Single-chamber pacemakers have one lead to carry impulses to and from either the right atrium or right ventricle.
A dual-chamber pacemaker characteristically has two leads, one to the right atrium and one to the right ventricle, which can allow a heart rhythm that more naturally resembles the normal activities of the heart and reflects intrinsic depolarization.
Temporary pacemakers — Temporary pacemakers are intended for short-term use during hospitalization. They are used because the arrhythmia is expected to be temporary and eventually resolve, or because the person requires temporary treatment until a permanent pacemaker can be placed.
Permanent pacemakers — Permanent pacemakers are pacemakers that are intended for long-term use.
As a general rule, permanent pacing is recommended for certain conditions that are chronic or recurrent and not due to a transient cause. Permanent pacing may be considered necessary or appropriate for certain people with symptomatic bradyarrhythmia or, less commonly, to help prevent or terminate tachyarrhythmia.
Implantation — The pacemaker is most commonly implanted into soft tissue beneath the skin in an area below the clavicle, which is known as prepectoral implantation; this is located under the skin and fat tissue but above the pectoral muscle. The pacemaker leads are typically inserted into a major vein (transvenously) and advanced until the leads are secured within the proper region(s) of heart muscle. The other ends of the leads are attached to the pulse generator (figure 2).
Less commonly, the pulse generator is placed under the skin of the upper abdomen.
Generally the pacemaker is implanted in a sterile laboratory or operating room by a specialist (cardiologist, surgeon, or cardiac electrophysiologist) with experience in this procedure. Local anesthesia and often conscious sedation are used to make the procedure as pain-free as possible. General anesthesia is rarely required. The position of the pacemaker leads is usually checked using X-ray imaging (called fluoroscopy). The length of the procedure depends upon the type of device being placed.
Recovery from the procedure is rapid, but there may be some restrictions on arm movement and activities for the first two to four weeks. Lead dislodgement is more common in the first few weeks after implantation. The hospital stay is usually brief, and the procedure can be performed as an outpatient.
Once implanted, pacemakers can be programmed to change the baseline heart rate, the upper heart rate at which the pacemaker will pace, and heart rate changes that should occur with exercise.
Follow-up care — People who have a permanent pacemaker will require periodic surveillance of the implanted device. The status of the pacemaker will be regularly checked or “interrogated” (often done by a programmer – a small briefcase kind device – with a telemetry wand placed over the skin where the pacemaker is implanted. Figure 3) to provide information regarding the type of heart rhythm, the functioning of the pacemaker leads, the frequency of utilization of the pacemaker, the battery life, and the presence of any abnormal heart rhythms. Nowadays, it can also be done remotely using a telephone or a secure web-based system from the patients’ home. Figure 4.
All contemporary devices are programmable with information and settings that can be altered and stored. Information is obtained by transmitting data from the pulse generator to a programmer, usually done during a follow-up office visit. However, with newer pulse generators it may be possible to obtain information about the pacemaker’s performance by downloading data from the patient’s device to the internet and then to the caregiver’s office. In older devices, pacemaker status can be checked routinely via the telephone using a trans-telephonic device.
The pulse generators are usually powered by lithium batteries that function for an average of five to eight years before they need to be replaced. When the batteries start to wear out, they do so in a very slow and predictable fashion, allowing sufficient time to be detected and pulse-generator replacement planned. Replacing the pulse generator usually requires a simple procedure in which a skin incision is made over the old incision, the old generator is removed, and a new generator is implanted and joined with the existing leads, assuming the existing leads are functioning normally.
The pacemaker leads are usually used indefinitely, unless a specific problem occurs (eg, the lead loses contact with the heart, the lead breaks, or the lead is not functioning properly). In such circumstances, the lead may require replacement. Often, the old lead is left in place but disconnected from the pulse generator and capped, and a new lead is inserted.
AVOIDING ELECTROMAGNETIC INTERFERENCE — Although contemporary pacemakers are less susceptible to interference than older models, electromagnetic energy can interfere in some cases. Thus, experts advise that people with pacemakers be aware of the following:
Household appliances — Pacemaker manufacturers do not recommend any special precautions when using normally functioning common household appliances such as microwave ovens, televisions, radios, toasters, and electric blankets.
Cellular phones — Evidence suggests that cellular phones do not cause interference with permanent pacemakers. While some older generation pacemakers and implantable cardioverter-defibrillators (ICDs) did occasionally experience interference from cellular telephones, clinical experience suggests that there is no significant interference between pacemakers or ICDs and modern wireless communication devices or portable media players.
Anti-theft systems — Electromagnetic anti-theft security systems are often found in or near the workplace, at airports, in stores, at courthouses, or in other high-security areas. Although interference with a pacemaker is possible, it is unlikely that any clinically significant interference would occur with the transient exposure associated with walking through such a field.
Metal detectors at airports — Similar to antitheft systems, metal detectors at airports can potentially interfere with pacemakers, although this is unlikely. Such exposure has been shown to cause interference in some cases and may be related to the duration of exposure and/ordistance between the security system and the pacemaker. Metal detectors will likely be triggered by the presence of a pacemaker and therefore at places such as airports, it will be important for individuals with pacemakers to carry an identification card for their pacemaker, and airport personnel will likely prefer to do a manual search.
External electrical equipment — External electrical fields do not seem to cause a problem for most people with a pacemaker. However, in workplaces that contain welding equipment or strong motor-generator systems, because interference can inhibit pacing, it is recommended that a person with an implanted cardiac device remain at least two feet from external electrical equipment, verify that the equipment is properly grounded, and leave the immediate locale if lightheadedness or other symptoms develop.
Diagnostic or therapeutic procedures — Certain types of surgery and procedures may interfere with pacemakers. Most importantly, the use of electrocautery can inhibit pacemaker function. It is not uncommon therefore that a pulse generator may require specific reprogramming before the procedure and programming back to its baseline condition after the procedure. In some instances, a magnet is all that is required on the device to make sure that there is no problem with the device during the procedure. Such procedures include:
Magnetic resonance imaging (MRI), which uses a strong magnetic field that is pulsed on and off at a rapid rate. For most patients with a pacemaker, this procedure is a relative contraindication. Nowadays, MRI-Safe pacemakers are available.
Transcutaneous electrical nerve/muscle stimulators (TENS), a method of pain control.
Diathermy, which heats body tissues with high-frequency electromagnetic radiation or microwaves.
Extracorporeal shock wave lithotripsy, the use of sound waves to break up gallstones and kidney stones.
Therapeutic radiation for cancer or tumors, which can cause permanent pacemaker damage.
Any surgery in which electrocautery is being used. The risks are greatest when the electrocautery is being performed close to the pulse generator.
Thus, doctors, dentists, and other healthcare providers should be informed about a person’s pacemaker. If a procedure associated with pacemaker interference is contemplated, the possible benefits, risks, and alternatives should be considered and discussed, as appropriate. People with pacemakers should carry a medical identification card for emergencies.
Figure 1. Image of Two Pulse Generators (only one is implanted) and pacing lead. The rear model is single chamber and one in front is dual chamber pacemaker. Models shown in this image are MRI-Safe pacemakers (see section on electromagnetic interference in text)
Figure 2. Diagrammatic representation of an implanted pacemaker. The pulse generator is placed under the skin below the left collar bone. Leads are inserted into the subclavian vein and their tips are placed in the right atrium and right ventricle.
Figure 3. A pacemaker patient being “interrogated” -checking of pacemaker -with the programmer device on the table and telemetry wand placed over the patient’s chest.
Figure 4. The Merlin remote monitoring solution enabling checking of pacemaker from patients’ home.
Micra “leadless” pacemaker – Micra is the latest in pacemaker technology – it is a very small capsule sized device that can be implanted in the heart directly through the vein in the groin, requiring no surgical incision. Figure 5
ASTRA XT pacemaker – This pacemaker is fully MRI compatible and has a life of 15 yrs, almost double that of conventional pacemakers. Figure 6
Figure 5. The MICRA “lead less” pacemaker. It’s the world’s smallest pacemaker and is implanted percutaneously without any surgery.
Figure 6. The ASTRA XT pacemaker with a life of 15 yrs.
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