Electromagnetic interference in critical care

Mobile communication and wireless data transmission are playing an increasing role in health care. Reports describing medical device malfunction related to cellular phones have raised awareness about the problem of electromagnetic interference. Although initial institutional responses were to ban cellular devices in hospitals, these restrictions are relaxing as the knowledge base in this area expands. Medical device malfunction is extremely rare if the distance from the transmitting device is greater than 1 m. This article reviews the current understanding of electromagnetic interference as it applies to the technology-rich critical care environment.     

Totally Implantable Wireless Ultrasonic Doppler Blood Flowmeters: Toward Accurate Miniaturized Chronic Monitors

Totally implantable wireless ultrasonic blood flowmeters provide direct-access chronic vessel monitoring in hard-to-reach places without using wired bedside monitors or imaging equipment. Although wireless implantable Doppler devices are accurate for most applications, device size and implant lifetime remain vastly underdeveloped. We review past and current approaches to miniaturization and implant lifetime extension for wireless implantable Doppler devices and propose approaches to reduce device size and maximize implant lifetime for the next generation of devices. Additionally, we review current and past approaches to accurate blood flow measurements. This review points toward relying on increased levels of monolithic customization and integration to reduce size. Meanwhile, recommendations to maximize implant lifetime should include alternative sources of power, such as transcutaneous wireless power, that stand to extend lifetime indefinitely. Coupling together the results will pave the way for ultra-miniaturized totally implantable wireless blood flow monitors for truly chronic implantation.     

Electromagnetic Interference of an Implantable Loop Recorder by Commonly Encountered Electronic Devices

De COCK, C.C., et al. : Electromagnetic Interference of an Implantable Loop Recorder by Commonly Encountered Electronic Devices. Electromagnetic interference of pacemaker systems has been well established and can lead to an inappropriate function of these devices. Recently, an implantable loop recorder (ILR) (REVEAL, Medtronic Inc.) has been introduced to evaluate the possible arrhythmic etiology of patients with recurrent syncope. We evaluated the interference of this device in two patients with implantable ILR and in three nonimplanted ILRs with four electromagnetic sources: cellular phones (GSMs), electronic article surveillance systems (EASs), metal detector gates (MDGs), and magnetic resonance imaging (MRI). The GSM did not affect appropriate function of the ILR whereas radiofrequency (RF) EAS could interfere with normal function in implanted and nonimplanted systems. The MDG had no influence on ILR function. The magnetic field induced by the MRI resulted in an irreversible error in one nonimplanted ILR. Therefore, although interference between electromagnetic sources and ILRs appears to be rare in our study, physicians should be aware of possible malfunctioning of these devices.     

Radiofrequency treatment of hepatic neoplasms in patients with permanent pacemakers

Clinicians who provide care for patients with implantable devices for rhythm management, ie, pacemakers and internal cardioverter defibrillators, must be aware of sources of interference that could affect device function. Intracardiac radiofrequency is a recognized source of potential interference. However, radiofrequency to extracardiac sites that are relatively close to the implanted device has not been investigated thoroughly. We present 2 patients with permanent pacemakers undergoing intrahepatic radiofrequency for the treatment of metastatic disease. No interference was documented in either patient. Additional in vitro and in vivo studies are needed to determine definite clinical guidelines for such patients.     

Potential for Personal Digital Assistant interference with implantable cardiac devices

OBJECTIVE: To determine whether the wireless local area network (WLAN) technology, specifically the Personal Digital Assistant (PDA), interferes with implantable cardiac pacemakers and defibrillators. MATERIAL AND METHODS: Various pacemakers and defibrillators were tested in vitro at the Mayo Clinic in Rochester, Minn, between March 6 and July 30, 2003. These cardiac devices were exposed to an HP Compaq IPAQ PDA fitted with a Cisco Aironet WLAN card. Initial testing was designed to show whether the Aironet card radiated energy in a consistent pattern from the antenna of the PDA to ensure that subsequent cardiac device testing would not be affected by the orientation of the PDA to the cardiac device. Testing involved placing individual cardiac devices in a simulator and uniformly exposing each device at its most sensitive programmable value to the WLAN card set to maximum power. RESULTS: During testing with the Cisco WLAN Aironet card, all devices programmed to the unipolar or bipolar configuration single- or dual-chamber mode had normal pacing and sensing functions and exhibited no effects of electromagnetic interference except for 1 implantable cardioverter-defibrillator (ICD). This aberration was determined to relate to the design of the investigators' testing apparatus and not to the output of the PDA. The ICD device appropriately identified and labeled the electromagnetic aberration as "noise." CONCLUSIONS: We documented no electromagnetic interference caused by the WLAN technology by using in vitro testing of pacemakers and ICDs; however, testing ideally should be completed in vivo to confirm the lack of any clinically important interactions.     

Implantable rhythm devices and electromagnetic interference: myth or reality?

Current medical guidelines have prompted implementation of increasing numbers of implantable rhythm devices, be they pacemakers, internal cardioverter-defibrillators or loop recorders. These devices rely on complex microcircuitry and use electromagnetic waves for communication. They are, therefore, susceptible to interference from surrounding electromagnetic radiation and magnetic energy. Hermetic shielding in metallic cases, filters, interference rejection circuits and bipolar sensing have contributed to their relative resistance to electromagnetic interference (EMI) in household and workplace environments. Device interactions have occurred in hospitals where EMI sources are ubiquitous, including radiation, electrocautery and MRI exposures. However, with rapidly evolving technology, devices and potential sources of EMI continue to change. This review provides a contemporary overview of the current state of knowledge regarding risks attributable to EMI; highlights current limitations of implantable rhythm devices; and attempts to distinguish myths from realities.     

Implantable rhythm devices and electromagnetic interference: myth or reality?

Current medical guidelines have prompted implementation of increasing numbers of implantable rhythm devices, be they pacemakers, internal cardioverter–defibrillators or loop recorders. These devices rely on complex microcircuitry and use electromagnetic waves for communication. They are, therefore, susceptible to interference from surrounding electromagnetic radiation and magnetic energy. Hermetic shielding in metallic cases, filters, interference rejection circuits and bipolar sensing have contributed to their relative resistance to electromagnetic interference (EMI) in household and workplace environments. Device interactions have occurred in hospitals where EMI sources are ubiquitous, including radiation, electrocautery and MRI exposures. However, with rapidly evolving technology, devices and potential sources of EMI continue to change. This review provides a contemporary overview of the current state of knowledge regarding risks attributable to EMI; highlights current limitations of implantable rhythm devices; and attempts to distinguish myths from realities.     

Mobile communication devices causing interference in invasive and noninvasive ventilators

PURPOSE: The aim of this study was to assess if common mobile communication systems would cause significant interference on mechanical ventilation devices and at what distances would such interference occur. MATERIALS AND METHODS: We tested all the invasive and noninvasive ventilatory devices used within our region. This consisted of 2 adult mechanical ventilators, 1 portable ventilator, 2 pediatric ventilators, and 2 noninvasive positive pressure ventilatory devices. We operated the mobile devices from the 2 cellular communication systems (digital) and 1 2-way radio system used in our province at varying distances from the ventilators and looked at any interference they created. We tested the 2-way radio system, which had a fixed operation power output of 3.0 watts, the Global Systems for Mobile Communication cellular system, which had a maximum power output of 2.0 watts and the Time Division Multiple Access cellular system, which had a maximum power output of 0.2 watts on our ventilators. The ventilators were ventilating a plastic lung at fixed settings. The mobile communication devices were tested at varying distances starting at zero meter from the ventilator and in all operation modes. RESULTS: The 2-way radio caused the most interference on some of the ventilators, but the maximum distance of interference was 1.0 m. The Global Systems for Mobile Communication system caused significant interference only at 0 m and minor interference at 0.5 m on only 1 ventilator. The Time Division Multiple Access system caused no interference at all. Significant interference consisted of a dramatic rise and fluctuation of the respiratory rate, pressure, and positive end-expiratory pressure of the ventilators with no normalization when the mobile device was removed. CONCLUSIONS: From our experiment on our ventilators with the communication systems used in our province, we conclude that mobile communication devices such as cellular phones and 2-way radios are safe and cause no interference unless operated at very close distances of less than 1 meter.     

Wireless technology in the ICU: boon or ban?

Wireless communication and data transmission are playing an increasing role in the critical care environment. Early anecdotal reports of electromagnetic interference (EMI) with intensive care unit (ICU) equipment resulted in many institutions banning these devices. An increasing literature database has more clearly defined the risks of EMI. Restrictions to the use of mobile devices are being lifted, and it has been suggested that the benefits of improved communication may outweigh the small risks. However, increased use of cellular phones and ever changing communication technologies require ongoing vigilance by healthcare device manufacturers, hospitals and device users, to prevent potentially hazardous events due to EMI.     

Cellular telephone interference with medical equipment

OBJECTIVE: To assess the potential electromagnetic interference (EMI) effects that new or current-generation cellular telephones have on medical devices. MATERIAL AND METHODS: For this study, performed at the Mayo Clinic in Rochester, Minn, between March 9, 2004, and April 24, 2004, we tested 16 different medical devices with 6 cellular telephones to assess the potential for EMI. Two of the medical devices were tested with both new and old interface modules. The 6 cellular telephones chosen represent the different cellular technology protocols in use: Code Division Multiple Access (2 models), Global System for Mobile communications, Integrated Digital Enhanced Network, Time Division Multiple Access, and analog. The cellular telephones were tested when operating at or near their maximum power output. The medical devices, connected to clinical simulators during testing, were monitored by observing the device displays and alarms. RESULTS: Of 510 tests performed, the incidence of clinically important interference was 1.2%; EMI was Induced in 108 tests (21.2%). Interference occurred in 7 (44%) of the 16 devices tested. CONCLUSIONS: Cellular telephones can interfere with medical equipment. Technology changes in both cellular telephones and medical equipment may continue to mitigate or may worsen clinically relevant interference. Compared with cellular telephones tested in previous studies, those currently in use must be closer to medical devices before any interference is noticed. However, periodic testing of cellular telephones to determine their effects on medical equipment will be required.     

AANA Journal Course: update for nurse anesthetists. Arrhythmia management devices and electromagnetic interference

The technological complexity of implantable arrhythmia management devices, specifically pacemakers and defibrillators, has increased dramatically since their introduction only a few decades ago. Patients with such devices are encountered much more frequently in hospitals and surgery centers, yet anesthesia provider knowledge of safe and proper management is often incomplete. Anesthesia textbooks and references may provide only short paragraphs on arrhythmia management devices that do not address important perioperative management strategies for this ever-growing patient population. It is no longer satisfactory to simply place a magnet over an implanted device during surgery and assume that this action protects the patient from harm due to electromagnetic interference from inappropriate device function. This AANA Journal course serves as a concise review of basic device function, the sources and effects of electromagnetic interference in the operative setting, and patient management recommendations from current literature.     

The Effects of Nuclear Magnetic Resonance Imagers on External and Implantable Pulse Generators

This study evaluates the effect of nuclear magnetic resonance (NMR) scanning on pacemaker function. It must be emphasized that each manufacturer's pulse generators and each pacing modality may behave differently and, therefore, require individual evaluation. According to our results, patients with pacemakers should have their pacing activity monitored continuously during scanning with the NMR 1500 gauss imaging system. External pulse generators should be set to the asynchronous mode and placed outside the NMR image volume but within the radiofrequency (RF) shield. Implanted pacemakers should be verified for type and mode of operation. All implantable pulse generators evaluated reverted from the demand to the asynchronous mode within the magnetic field of the scanner. There was no observable damage to the discrete pacemaker components that were tested. In vivo testing of implantable single-chamber pulse generators did not significantly alter the pacemaker's operating parameters. Changes in stimulation rate analogous to the RF field pulse rate were seen. In single-chamber devices the resultant rate was a multiple of the RF frequency, changing to a value less than the normal asynchronous magnetic rate. With more sophisticated dual-chamber devices the results varied. With VDD pacing during RF scanning, the cardiac stimulation rate increased to a value analogous to the RF field modulation period. More extensive in vivo testing using different models of pulse generators of various manufacturers is needed to identify specific device susceptibility to the RF, time variance and steady-state magnet fields. From these data a comprehensive statement about NMR scanning of patients with implanted pacemakers can be made.     

Infrared transmission of electronic information via LAN in the operating room

Recent advances in technology have brought many kinds of monitoring devicesinto the operating room (OR). The information gathered by monitors can bechanneled to the operating ward information system via a local area network(LAN). Connecting patients to monitors and monitors to the LAN, however,requires a large number of cables. This wiring is generally inconvenient andparticularly troublesome if the layout of the OR is rearranged. From thispoint of view, wireless transmission seems ideally suited to clinicalsettings. Currently, two modes of wireless connectivity are available:radio-frequency (RF) waves or infrared (IR) waves. Some reports suggest thatRF transmission is likely to cause electromagnetic interference (EMI) inmedical devices such as cardiac pacemakers or infusion pumps. The risk ofmalfunctioning life-sustaining devices and the catastrophic consequences thiswould have on seriously ill patients rules out the use of RF. Here, we reportan IR system using IR modems for LAN connectivity in the OR. In this study,we focused on the possible detrimental effects of EMI during wirelessconnectivity. In our trial, we found no evidence of EMI of IR modems with anyof the medical devices we tested. Furthermore, IR modems showed similarperformance to a wired system even in an electrically noisy environment. Weconclude that IR wireless connectivity can be safely and effectively used inORs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Avoidance of electromagnetic interference to implantable cardiovertor-defibrillator during atrioventricular node ablation for atrial fibrillation using transvenous cryoablation

Transient or permanent malfunction of implantable device may result from electromagnetic interference during delivery of radiofrequency energy for treatment of cardiac arrhythmias. Therefore, there is a clinical need for an alternative energy source for cardiac arrhythmia ablation in patients with implantable device. This report presents a case of the absence of electromagnetic interference to an implantable cardioverter defibrillator during atrioventricular nodal ablation for atrial fibrillation to avoid inappropriate shock.     

Overcoming Electromagnetic Interference by LVADs on ICD Function by Shielding the ICD Programmer Wand and Extension Cable

Patients with end-stage cardiomyopathy and congestive heart failure are increasingly undergoing implantation with left ventricular assist devices (LVADs). In addition, implantable cardioverter-defibrillator (ICD) therapy has been proven to be an important part of the treatment for cardiomyopathy/congestive heart failure. Previous reports have noted a potential and dramatic electromagnetic interference from LVADs on ICDs that cause impaired telemetry communication between the ICD and ICD programmer. Such interference has necessitated explantation and generator replacement in order to resume communication between the ICD and programmer. We report two patients with advanced congestive heart failure and ICD programming impairment caused by a HeartMate II LVAD (Thoratec Corporation, Pleasanton, CA, USA) that was overcome by placing aluminum shielding around the ICD programmer wand and steel shielding around the extension cable during ICD interrogation.     

Finite element analysis and fatigue of stents

Understanding the behaviour of implantable medical devices is of obvious importance. The potential for failure of a medical device can often be associated with issues related to cyclic loading of the device, and material fatigue. Detailed finite element simulations to evaluate the fatigue of stents allow the engineer to assess potential failures. The engineer can then use the analysis results to modify the design and prevent failure, without making and testing numerous physical devices. Complete understanding of the mechanical behaviour of a stent provided by finite element analysis has the benefits of facilitating effective design, helping to reduce time to market and minimising the potential for unwanted failures.     

Cardiac CT: Imaging of and Through Cardiac Devices

For patients with cardiac devices, cardiac computed tomography (CT) remains the mainstay for imaging due to its superior resolution as compared with echocardiography and nuclear studies and no contraindication to metal as with cardiac magnetic resonance imaging. This review focuses on the evaluation and pitfalls of coronary arterial imaging in patients with devices, such as pacemakers, implantable defibrillators, cardiac resynchronization therapy (CRT), as well as complications such as lead perforation and safety concerns of CT interference. We discuss both pre- and post-procedural CRT assessment for coronary venous imaging and pre-procedural myocardial scar assessment to localize regions of scar and peri-infarct zone to facilitate ventricular tachycardia ablation in patients with devices. We describe potential new research on dyssynchrony and integration with myocardial scar and site of latest activation for patients with or being considered for CRT. We detail the utility of CT for the assessment of proper function and complications in patients with left ventricular assist device implantation.     

Left Ventricular Mechanical Assist Devices and Cardiac Device Interactions: An Observational Case Series

Background: Nonpulsatile left ventricular assist devices (LVADs) are increasingly used for treatment of refractory heart failure. A majority of such patients have implanted cardiac devices, namely implantable cardioverter-defibrillators (ICDs) or cardiac resynchronization therapy-pacemaker (CRT-P) or cardiac resynchronization therapy-defibrillator (CRT-D) devices. However, potential interactions between LVADs and cardiac devices in this category of patients remain unknown.
Methods: We reviewed case records and device logs of 15 patients with ICDs or CRT-P or CRT-D devices who subsequently had implantation of a VentrAssist LVAD (Ventracor Ltd., Chatswood, Australia) as destination therapy or bridge to heart transplantation. Pacemaker and ICD lead parameters before and after LVAD implant were compared. In addition, ventricular tachyarrhythmia event logs and potential electromagnetic interference reports were evaluated.
Results: Right ventricular (RV) sensing decreased in the first 6 months post-LVAD. Mean R-wave amplitude preimplant was 10.9 ± 5.25 mV compared with 7.2 ± 3.4 mV during follow-up (P = 0.02). RV impedance also decreased from 642 ± 240 ohms at baseline to 580 ± 212 ohms at follow-up (P = 0.007). There was a significant increase in RV stimulation threshold following implantation of the LVAD from 0.8 ± 0.6 V at baseline to 1.4 ± 1.0 V in the first 6 months postimplant (P = 0.01). A marked increase in ventricular tachyarrhythmia burden was observed in three patients. One patient displayed electromagnetic interference between the LVAD and defibrillator, resulting in inappropriate defibrillation therapy.
Conclusions: LVADs have a definite impact on cardiac devices in respect with alteration of lead parameters, ventricular tachyarrhythmias, and electromagnetic interference.     

Cellular phone interference with external cardiopulmonary monitoring devices

OBJECTIVES: To determine the potential effect (electromagnetic interference) of cellular telephones on external cardiopulmonary monitoring devices. METHODS: For this study, we tested 17 different medical devices with 5 portable telephones (4 digital, 1 analog) to assess the potential for electromagnetic interference. The telephones were tested in a normal operating mode to simulate a typical hospital environment with patients or their families using their cellular phones. The medical devices were connected to the appropriate simulators for proper operation while the tests were under way. The screens and alarms of the medical devices were monitored while the telephones were maneuvered in the y and z planes near the devices. Clinically important interference was defined as interference that may hinder interpretation of the data or cause the equipment to malfunction. RESULTS: Any type of interference occurred in 7 (41%) of the 17 devices tested during 54.7% of the 526 tests. The incidence of clinically important interference was 7.4%. CONCLUSIONS: Cellular telephones may interfere with the operation of external cardiopulmonary monitoring devices. However, most of the test results showed that the interference would rarely be clinically important.     

Effect of bioimpedance body composition analysis on function of implanted cardiac devices

Background: It is routinely recommended that patients with pacemakers, implantable cardioverter defibrillators (ICD), and cardiac resynchronization therapy‐defibrillators (CRT‐D) avoid bioelectrical impedance analysis (BIA)—a commonly used method to estimate body composition—because of the concern for the potential for BIA interference with pacemaker or ICD function. However, the prevalence of such interference is not known. Objective: Assess for incidence of interference between BIA and ICD or CRT‐D devices. Methods and Results: Twenty patients with heart failure and cardiac implanted electronic devices (50% ICD, 50% CRT‐D) underwent BIA during real‐time device interrogation to detect interference. Study patients were 90% male, with mean age 54 ±14 years, and mean LVEF 23 ± 11%. Devices from all four leading cardiac device manufacturers were included. Device therapies were temporarily disabled to prevent inappropriate shocks. During body composition testing using BIA, no evidence of interference with ICD function was seen in any patient, including no telemetry disruption, no oversensing on any lead, and no patient symptoms. Conclusions: Despite the manufacturers’ recommendation to avoid BIA in patients with ICDs, this study showed no evidence of any interference in 20 patients. Bioimpedance analysis might be safe in such patients, but further confirmatory studies are required. (PACE 2012; 35:681–684)