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In an environment where we are being increasingly surrounded by developing technology, pacemaker patients are questioning the possible effects of the increasing associated environmental and electromagnetic "noise" on their implants.
It should be stated quite clearly that, despite the increased prevalence of interference, clinically significant problems remain uncommon and that the continual improvement in pacemaker protection circuitry design evident in the industry, should keep the incidence low.
The following is a brief review of currently identified sources of interference and their likely effects on the modern pacemaker system.
Note: It should be understood that the responses to interference described in this review apply to pacemaker systems in general and do not specifically apply to, nor are they documented behavior of, Cardiac Control Systems' products.
The application of design standards employed by most pacemaker manufacturers (Cardiac Control Systems conforms to EN 45502) includes investigating the effects of interference on a pacemaker design prior to product release to the marketplace. While the application of such standards provides some assurance, it remains that Ionizing Radiation, Ultrasonic, and Electromagnetic Interference (EMI) from a wide range of sources have the undoubted potential to disrupt the normal behavior of an implanted pacemaker.
A pacemaker system's response to interference depends on a number of variables including, but not limited to, the nature and strength of the interfering signal, the proximity of the patient to the source, and the pacemaker's design as this relates to the signal, including the degree of shielding as well as its sensing and polarity characteristics.
Most pacemaker circuitry uses filters to attenuate electromagnetic interference (EMI) outside the normal intracardiac range and, whereas this design is effective when the interference characteristics are quite different from detected signals associated with cardiac activity, some EMI can produce signals that are similar enough to normal intracardiac activity to cause problems.
The range of responses from the pacemaker system to EMI and other forms of interference is wide and largely depends on the interference signal characteristics. Possible pacemaker responses to interference include:
These responses are almost always temporary and only occur while the patient remains in range of the source of interference. In extreme cases, where the interference is of a sufficiently high magnitude, it is possible for the pacemaker circuitry to be damaged, leading to a continued abnormal pacing behavior. There are several different categories of common environmental interference, these include:
This is possibly the most common environmental source. No direct contact with the patient is required. It is commonly seen around:
The likelihood of interference from electrically coupled sources of interference increases with the strength of the source and with the proximity of the pacemaker to the source. Moving away from the source of interference will usually return the pacemaker to normal behavior.
Occurs when a patient comes in close contact (no direct contact with the patient is required) with an intense magnetic field such as:
The likelihood of interference from magnetically coupled sources of interference increases with the strength of the source and with the proximity of the pacemaker to the source. Moving away from the source of interference will usually return the pacemaker to normal behavior.
This type of interference requires that the pacemaker patient be in direct contact with an electrical current, for example:
The likelihood of interference from galvanically coupled sources of interference increases with the strength of the source and with the degree of contact with the current. Disengaging contact from the source of interference will usually return the pacemaker to normal behavior.
These sources of interference are normally only encountered in the hospital/clinic environment where the staff is informed of requisite precautions appropriate for a pacemaker patient.
This source of interference and possible damage (see the listing of common interference sources at the end of this review) to pacemaker circuitry is only encountered in the hospital/clinic environment where the staff will take the requisite precautions with a pacemaker patient.
Cardiac Control Systems and other manufacturers have a number of specific cautions regarding environmental and therapeutic hazards to pacemaker systems. CCS cautions are as follows:
Electromagnetic Interference (EMI)
EMI presents a potential hazard to proper pacemaker operation. All pacemakers that incorporate a sensing function are susceptible to EMI with frequency contents that mimic cardiac signals. Common sources of electromagnetic signals include MRI, electrocautery, defibrillation equipment, welding equipment, and electric motors. Sensed EMI can cause pacing inhibition, triggering, or reversion to the pulse generator's noise response. The Maestro II series pacing system has been designed with a special mechanism for protection against the hazards of EMI, but complete immunity from all environmental hazards cannot be provided.
Electromagnetic interference of sufficient magnitude to be detected by Maestro II series pulse generators, results in noise response mode behavior. Elimination of the interference will result in resumption of normal pacing at the programmed values.
Defibrillation
Defibrillation procedures can produce a large current flow between the stimulating electrode(s) and the pulse generator case in unipolar pacing systems. Damage to the pulse generator may occur, typically resulting in loss of output capability. In addition, thermal damage to the heart may occur at the electrode/tissue interface(s). To minimize the risks with pectorally implanted unipolar pacing systems use the following recommendations:
Diathermy
Recommendations:
Electrocautery
Surgical application of electrocautery can inhibit or trigger the pacemaker in demand modes, damage the pacing system, or possibly cause the unit to go into its Automatic Safety Reversion mode. Electrocautery can also cause thermal damage to the heart through the lead electrode.
Recommendations:
Lithotripsy
The presence of a cardiac pacemaker is considered a contraindication to extracorporeal electrohydraulic shock wave Lithotripsy, due to the possibility of electrical interference from the spark gap used to produce the shock waves, or damage to the pulse generator from the shock waves. Studies indicate that Lithotripsy shock effects on cardiac pacemakers (with the exception of those incorporating piezoelectric activity sensors) can generally be safely tolerated provided these rules are followed:
Recommendations:
Magnetic Resonance Imaging (MRI)
MRI should not be used with pacemaker patients. The intense magnetic fields generated by MRI can affect pacemaker performance and may damage pulse generator circuitry.
Radiotherapy
Diagnostic radiation levels may be safely used. However, therapeutic levels of ionizing radiation in cumulative doses as low as 1,000 rads have been shown to adversely affect the operation of some cardiac pulse generators. Pulse generators incorporating complementary metal-oxide semiconductor (CMOS) circuitry are particularly susceptible and may exhibit unpredictable failure modes.
If high-dose radiotherapy is required for a pacemaker patient:
Recommendations:
Home Appliances
Microwave ovens and other electrical home appliances present no specific problems to the patient or pacing system if such appliances are operating normally. However, some electrical or gasoline-powered equipment can cause inhibition or triggering of the pacemaker in demand modes. This equipment includes the following:
In general, such devices may be safely used by pacemaker patients provided protective hoods or shrouds are left in place during operation. The patient should not, however, work on the ignition systems of gasoline-powered devices while they are in operation.
Industrial and Special Environments
Certain industrial and special environments contain intense electromagnetic fields that can affect proper pacemaker operation. The device should not be programmed to an inhibited pacing mode in pacemaker patients expected to come into contact with fields such as those emitted by the following:
Cellular Telephones (Text in this section from the HIMA (Health Industry Manufacturers Association) Pacemaker Task Force Labeling recommendations.)
Recent studies have indicated there may be a potential interaction between cellular phones and pacemaker operation. Potential effects may be due to either the radio frequency signal or the magnet within the phone and could include inhibition or asynchronous pacing when the phone is in close proximity (within 15 cm or 6 inches) to the pulse generator. It is important to note that any effect resulting from an interaction between cellular phones and implanted pacemakers is temporary. Simply moving the phone away from the implanted device will return the device to its previous state of operation. Because of the great variety of cellular phones and the wide variance in patient physiology, an absolute recommendation to cover all patients cannot be made. The following information provides general guidelines to patients having an implanted pacemaker who desire to operate a cellular phone.
Recommendations:
There are many sources of interference that have the potential to interrupt the appropriate behavior of, or even cause damage to, an implanted pacemaker system. The successful design of modern pacemakers will ensure that most patients experience few or no problems, nevertheless, in cases of particularly strong interference coupled with close proximity of the patient to the source, pacemakers will respond in a variety of ways.
We suggest that pacemaker patients, particularly those who wish to continue working in potentially interference-rich environments, be counseled by their cardiologist on the effects of environmental interference and the likely response of their pacemaker system to the interference, as well as to the most effective ways of avoiding interference in their specific environment.
A listing of common interference sources and typical pacemaker responses follows.
We make no claims that the following list is complete, only that it represents common interference sources and typical pacemaker responses by systems from all manufacturers.
Ablation (DC):
The high electrical energy from DC (Direct Current) ablation can permanently damage circuitry and may lead to a no output response, sensing anomalies, erratic pacing, or rate increase on impedance-based rate responsive pacers.
Ablation (RF):
Loss of capture or exit block is frequently seen during RF (Radio Frequency) ablations. Arrhythmia induction, undersensing, inhibition, rate increase and noise reversion pacing are also possible. Circuit damage is less likely than with DC ablation.
Acupuncture (specifically electro-acupuncture):
Low frequency electro-acupuncture may cause inhibition. High frequency therapy may cause noise reversion. Traditional acupuncture, without electrical stimulation, is not a known source of EMI.
Airport detector:
Single beat inhibition is rare but occasionally seen. Anti-theft devices: Inhibition has been reported. See also Electronic article surveillance (EAS).
Arc welders:
Single beat inhibition is commonly seen. High magnetic fields from the cables may cause magnet response, resulting in asynchronous pacing.
Cardioversion:
Cardioversion, when performed at high energies similar to defibrillation or when performed directly over the pacemaker, may damage circuitry. This may result in no output, erratic pacing, or rate increases. Energy conducted through the lead may cause arrhythmias and myocardial burning.
Cautery:
Cautery used near the pacing system may result in inhibition, asynchronous pacing and/or circuit damage. Energy conducted through the lead may cause arrhythmias and myocardial burning. Impedance-based rate responsive pacemakers may exhibit erratic pacing or rate increases.
CB radio:
Some devices may exhibit single beat inhibition when the microphone key is pressed.
Cellular Phone:
Total inhibition or noise reversion pacing is possible with cell phones placed in close proximity to the pacemaker. Rate increases have been reported in DDD mode due to atrial tracking response.
Defibrillation:
Defibrillation performed at high energies, or defibrillation performed directly over the pacemaker, may damage circuitry. This may result in no output, erratic pacing, or rate increases. Energy conducted through the lead may cause arrhythmias and myocardial burning.
Dental scaler:
Older ferromagnetic ultrasonic scalers may cause single beat inhibition. The more modern piezoelectric scalers have no effect. Activity rate responsive devices may exhibit increased pacing rates.
Diathermy:
When used near the pacing system, diathermy may result in inhibition, asynchronous pacing, and/or circuit damage. Energy conducted through the lead may cause arrhythmias and myocardial burning.
Drill, electric:
Single beat inhibition is rare but may occur.
Electric blanket: Single beat inhibition is rare but may occur.
Electric shaver:
Single beat inhibition is rare but may occur. Placement directly over the pacemaker may result in magnet mode response.
Electric switch:
Single beat inhibition may be seen.
Electro-Convulsive Shock Therapy (ECT/EST):
Inhibition and/or noise reversion is possible. Activity sensor rate responsive pacemakers may track the seizure activity.
Electronic article surveillance (EAR):
Inhibition reported. An increased incidence of cross-talk has been observed on unipolar DDD pacers. See also Anti-theft devices.
Electrotome (dental device):
Single beat inhibition is rare but may occur.
Ham radio:
Single beat inhibition may be seen devices during microphone keying. There is some evidence that powerful transmitters themselves may result in inhibition.
Heating pad:
Single beat inhibition is rare, but may occur.
Lithotripsy:
No effect on VVI and VOO pacemakers' pulse rate. DDD pacemakers may track to maximum rate or totally inhibit ventricular output. Activity sensor rate responsive pacemakers may also track to maximum rate or be permanently damaged (piezo crystal may shatter near focal point).
Metal detector:
Single beat inhibition is rare but may occur.
Microwave ovens:
In 1976, the FDA stated that microwave ovens no longer posed substantial risk of pacemaker interference because the ovens are now built with leakage protection. Furthermore, pulse generators are now manufactured to prevent interference from microwaves.
Magnetic Resonance Imaging (MRI):
MRI is contraindicated.
Frequent effects from MRI are: asynchronous pacing, rapid pacing (300 PPM), reed switch/telemetry coil magnetization, rate increases in DDD, single beat inhibitions, component damage, lead dislodgment, and pacemaker movement within the pocket that has the potential to injure the patient.
PET scanner:
Possible CMOS damage. See Radiation.
Power lines, high voltage:
400 Kilovolt high voltage power lines may cause asynchronous pacing, especially if patient is near a large metal object (i.e. car).
Pulp tester:
Single beat inhibition is rare, but may occur.
Radar:
Single beat inhibition is rare, but may occur.
Radiation, diagnostic (Dx):
No effect, even with cumulative doses.
Radiation, therapeutic (Rx):
CMOS circuitry has failed on some pacemakers with doses as low as 1000 rads. Effect is cumulative in dose and affects both bipolar and unipolar pacemakers. Failure modes include circuit damage, run-away pacer, erratic pacing, sensing anomalies, and no output.
Radio transmitter, AM:
If signal modulation occurs, inhibition may be seen, relative to power, frequency, modulation, and proximity.
Radio transmitter, FM:
If signal modulation occurs, inhibition may be seen, relative to power, frequency modulation, and proximity. Noise reversion pacing is possible.
Respiratory monitors:
Impedance-based respiratory monitors may cause upper rate pacing in impedance based pacemakers, especially with monitors emitting a current signal parallel to the pacer system.
TENS (transcutaneous electrical nerve stimulators):
Normally used at high frequencies (>30 Hz), and low frequencies (<10 Hz) may cause inhibition on unipolar pacemakers. Burst mode is likely to produce total inhibition.
TV transmitter: (not TV set!)
Although rare, inhibition has been documented.
Ultrasound, diagnostic (Dx):
No effect.
Ultrasound, therapeutic (Rx):
Single beat inhibition is rare but may occur. Therapy should not be given directly over the pacemaker. Activity sensor rate responsive pacemakers may exhibit piezo crystal shatter.
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