Interference in implanted cardiac devices, part II

Radiofrequency and microwave tumor ablation in patients with implanted cardiac devices: is it safe?

PURPOSE

To identify malfunction of implanted cardiac devices during or after thermal ablation of tumors in lung, kidney, liver or bone, using radiofrequency (RF) or microwave (MW) energy.

MATERIALS AND METHODS

After providing written consent, 19 patients (15 men and 4 women; mean age 78 years) with pacemakers or pacemaker/defibrillators underwent 22 CT image-guided percutaneous RF or MW ablation of a variety of tumors. Before and after each procedure, cardiac devices were interrogated and reprogrammed by a trained cardiac electrophysiology fellow. Possible pacer malfunctions included abnormalities on electrocardiographic (EKG) monitoring and alterations in device settings. Our institutional review board approved this Health Insurance Portability and Accountability Act-compliant study. Informed consent for participation in this retrospective study was deemed unnecessary by our review board.

RESULTS

During 20 of 22 sessions, no abnormalities were identified in continuous, EKG tracings or pacemaker functions. However, in two sessions significant changes, occurred in pacemaker parameters: inhibition of pacing during RF application in one, session and resetting of mode by RF energy in another session. These changes did not, result in hemodynamic instability of either patient. MW ablation was not associated with, any malfunction. In all 22 sessions, pacemakers were undamaged and successfully reset to original parameters.

CONCLUSION

RF or MW ablation of tumors in liver, kidney, bone and lung can be performed safely in patients with permanent intra-cardiac devices, but careful planning between radiology and cardiology is essential to avoid adverse outcomes.

Exposure of non-target tissues in medical diathermy

With different prevalence in different regions, radio frequency (RF) electromagnetic fields (EMF) are widely used for therapeutic tissue heating. Although short-wave diathermy (27.12 MHz) is the most popular treatment modality, quantitative data on patient's exposure have been lacking. By numerical simulation with the numerical anatomical model NORMAN, intracorporal distributions of specific absorption rates (SAR) were investigated for different treatment scenarios and applicators. Quantitative data are provided for exposures of target treatment areas as well as for vulnerable regions such as the eye lenses, central nervous system, and testes. Different applicators and distances were investigated. Capacitive and inductive applicators exhibit quite a different heating efficiency. It could be shown that for the same output power therapeutic heat deposition can vary by almost one order of magnitude. By mimicking therapist's practice to use patient's heat perception as an indicator for output power setting, numerical data were elaborated demonstrating that muscle tissue exposures may be several times higher for inductive than for capacitive applicators. Presented quantitative data serve as a guide for power adjustment preventing relevant overexposures without compromising therapy; they also provide a basis for estimating target tissue heat load and developing therapeutic guidelines.

Computed Tomography Scan and ICD Interaction

Although it has been considered a safe procedure, computed tomography scanning uses high doses of radiation and can cause malfunctioning in those patients with ICD when the radiation is directly incident on the device. We present a case of ventricular oversensing during a thoracic computed tomography.

Defibrillator reset by radiotherapy

The number of patients with implantable cardioverter-defibrillator (ICD) is rapidly increasing due to their expanding indications. Amongst the various types of electromagnetic interferences, little is reported about the effects of radiotherapy. We report a case of electrical reset of a single chamber ICD by scattered irradiation from radiotherapy.

[Effect of diagnostic X-rays on implantable cardiac pacemakers and implantable cardioverter defibrillators, and its management]

The effects of diagnostic X-rays on implantable cardiac pacemakers and implantable cardioverter defibrillators (ICDs) were investigated. A total of 33 pacemakers from six manufacturers and nine ICDs from four manufacturers were irradiated using several X-ray units (plain X-ray diagnostic unit, under-table system fluoroscopy unit, over-table system fluoroscopy unit, biplane cardiac digital angiography unit, DSA unit and cone-beam CT unit). No systematic reset phenomena were observed in any pacemakers and ICDs under the X-ray irradiation. Nevertheless, over-sensing associated with the lack of a few pulses was observed in three of 33 pacemakers under radiation exposure. It has been proven that diagnostic X-rays might affect pacemaker function. Since the duration of the over-sensing under the radiation was very short and included transient episodes, this sensing failure, therefore, induced by radiation exposure would not affect the health of pacemaker recipients. ICDs were not affected by radiation exposure at a clinical dose. It is recommended that caution be exercised in direct irradiation to the pacemaker. Using a copper sheet of 2.0 mm thickness or more prevented over-sensing of pacemakers in the present study, especially when serial X-ray exposures were used with an over-table fluoroscopy system or cone-beam CT unit.

Risk of interference from transcutaneous electrical nerve stimulation on the sensing function of implantable defibrillators

BACKGROUND

The use of transcutaneous electrical nerve stimulation (TENS) for pain relief is increasing. At the same time the implantable cardioverter defibrillator (ICD) is a routine treatment for malignant tachyarrhythmias. Today patients often need devices for more than one condition, and consideration must be given to the interaction between them. We studied the risk of interference between TENS and the ICD function.

METHODS AND RESULTS

Thirty patients who had received an ICD underwent a test protocol including TENS at the mammilla and hip levels, at two energy levels, and at the highest comfortable stimulation level. The effects of TENS on the electrocardiogram lead II, intracardiac electrograms, and the ICD marker channels were analyzed. Disturbance from TENS on the sensing function was seen at all stimulation attempts. Interference between the systems was observed in 16 patients. In eight patients (27%) the interpretation was VT/VF and in 14 patients (47%) as ventricular premature extra beats. Other kinds of interactions were seen in five patients (16%). Each patient could have more than one kind of interference.

CONCLUSIONS

Noise reversion and undersensing might prevent the ICD from delivering shock when it should and the interpretation as VT/VF could result in inappropriate shocks. Because of the potentially serious consequences of interference we do not recommend the use of TENS in patients with ICD.

The patient with a cardiac pacemaker or implanted defibrillator and management during anaesthesia

PURPOSE OF REVIEW

Worldwide, nearly 3 million patients have cardiac pacemakers and more than 300,000 have implantable cardioverter-defibrillators. Many factors cause confusion regarding perioperative care of these patients, since conventional wisdom, case reports, textbooks, and literature reviews have either not kept pace with technologic developments or contain incorrect statements. Additionally, recalls or alert notices have prompted programming changes that might not be understood or recognized.

RECENT FINDINGS

The complexity of the devices, as well as features designed to improve both the quality of life and the survival of the patient, can masquerade as pacing malfunction. Additionally, algorithms designed to detect heart rate, ST segment behavior, and arrhythmias in electrocardiographic monitors may lead to inappropriate behavior on the part of the perioperative team.

SUMMARY

Appropriate education of perioperative practitioners, as well as preoperative interrogation of a pacemaker or implantable cardioverter-defibrillator, may prevent perioperative delays, cancellations, and deaths. Additionally, evidence suggests that postoperative re-interrogation of any cardiac generator is warranted if an operative event includes the use of monopolar electrosurgery ('Bovie') or significant fluid or blood component administration.

Effects of CT Irradiation on Implantable Cardiac Rhythm Management Devices1

PURPOSE

To prospectively measure the response of a variety of models of implantable cardiac rhythm management devices (ICRMDs) to the radiation delivered by computed tomography (CT), for both maximum and typical dose levels.

MATERIALS AND METHODS

Twenty-one ICRMDs (13 pacemakers, eight cardioverter-defibrillators) manufactured by Medtronic (Minneapolis, Minn) were exposed to ionizing radiation from CT systems in both spiral and dynamic acquisition modes at maximum and typical dose levels. Devices were monitored during exposure to check for any operational abnormalities and were interrogated after exposure to check for any residual abnormalities. Total radiation dose and peak dose rate were measured, and the volume CT dose index was recorded.

RESULTS

Oversensing was observed in 20 of 21 devices at maximum doses and in 17 of 20 devices at typical doses. Oversensing most often manifested as inhibition, although it occasionally manifested as tracking or safety pacing. Two devices inhibited for more than 4 seconds in spiral mode at clinical dose levels. Oversensing was transient and ceased as soon as the device stopped moving through the x-ray beam or the beam was turned off. The partial electrical reset (PER) safety feature was activated in two models, InSync 8040 and Thera DR. With the exception of PER, programming was not altered. Effects occurred only if the x-ray beam passed directly over the ICRMD.

CONCLUSION

CT irradiation at typical clinical doses results in oversensing of ICRMDs in the majority of devices tested, although the identified effects were predominantly transient.

Temperature and SAR measurement errors in the evaluation of metallic linear structures heating during MRI using fluoroptic probes

The purpose of this work is to evaluate the error associated with temperature and SAR measurements using fluoroptic temperature probes on pacemaker (PM) leads during magnetic resonance imaging (MRI). We performed temperature measurements on pacemaker leads, excited with a 25, 64, and 128 MHz current. The PM lead tip heating was measured with a fluoroptic thermometer (Luxtron, Model 3100, USA). Different contact configurations between the pigmented portion of the temperature probe and the PM lead tip were investigated to find the contact position minimizing the temperature and SAR underestimation. A computer model was used to estimate the error made by fluoroptic probes in temperature and SAR measurement. The transversal contact of the pigmented portion of the temperature probe and the PM lead tip minimizes the underestimation for temperature and SAR. This contact position also has the lowest temperature and SAR error. For other contact positions, the maximum temperature error can be as high as -45%, whereas the maximum SAR error can be as high as -54%. MRI heating evaluations with temperature probes should use a contact position minimizing the maximum error, need to be accompanied by a thorough uncertainty budget and the temperature and SAR errors should be specified.

Sonic and ultrasonic scalers in periodontal treatment: a review

Periodontal therapy aims at arresting periodontal infection and maintaining a healthy periodontium. The periodic mechanical removal of subgingival microbial biofilms is essential for controlling inflammatory periodontal disease. Mechanical periodontal therapy consists of scaling, root planing and gingival curettage. The sonic and ultrasonic scalers are valuable tools in the prevention of periodontal disease. The vibration of scaler tips is the main effect to remove the deposits from the dental surface, such as bacterial plaque, calculus and endotoxin. However, constant flushing activity of the lavage used to cool the tips and cavitational activity result in disruption of the weak and unattached subgingival plaque. The aim of the study was to review the safety, efficacy, role and deleterious side-effects of sonic and ultrasonic scalers in mechanical periodontal therapy.

Potential interference of small neodymium magnets with cardiac pacemakers and implantable cardioverter-defibrillators

BACKGROUND

Magnetic fields may interfere with the function of cardiac pacemakers and implantable cardioverter-defibrillators (ICDs). Neodymium-iron-boron (NdFeB) magnets, which are small in size but produce strong magnetic fields, have become widely available in recent years. Therefore, NdFeB magnets may be associated with an emerging risk of device interference.

OBJECTIVE

We conducted a clinical study to evaluate the potential of small NdFeB magnets to interfere with cardiac pacemakers and ICDs.

METHODS

The effect of four NdFeB magnets (two spherical magnets 8 and 10 mm in diameter, a necklace made of 45 spherical magnets, and a magnetic name tag) was tested in forty-one ambulatory patients with a pacemaker and 29 patients with an ICD. The maximum distance at which the magnetic switch of a device was influenced was observed.

RESULTS

Magnetic interference was observed in all patients. The maximum distance resulting in device interference was 3 cm. No significant differences were found with respect to device manufacturer and device types.

CONCLUSION

Small NdFeB magnets may cause interference with cardiac pacemakers and ICDs. Patients should be cautioned about the interference risk associated with NdFeB magnets during daily life.

Electrosurgery in Patients With Pacemakers/Implanted Cardioverter Defibrillators

Despite improved protective mechanisms, pacemakers and implanted cardioverter defibrillators are subject to interference from various sources. An effective means of hemostasis, electrocautery generates electromagnetic interference and may be problematic in this patient population. Reported complication rates are low, but the consequences can be serious. Recommendations regarding the management of patients with implanted cardiac devices become increasingly significant both as the number of patients with devices increases and the number of out-of-hospital/minor surgery procedures performed increases. This article provides surgeons and anesthetists with practical recommendations for use of electrocautery in patients with pacemakers or implantable cardiac defibrillators.

Strategies for the safe magnetic resonance imaging of pacemaker-dependent patients

OBJECTIVE

To determine if strategies used to safely scan nonpacemaker-dependent patients could be applied to facilitate safe MRI of pacemaker-dependent patients.

INTERVENTIONS

Ten pacemaker-dependent patients underwent a total of 11 MRI scans of the head and neck. Screening, reprogramming VOO or DOO at 60 ppm, and monitoring strategies were used to facilitate MRI. A transmit-receive coil was used and MRI pulse sequences were modified to limit the whole-body specific absorption rate (SAR).

RESULTS

All scans proceeded uneventfully. No difficulties in post-MRI telemetry or interrogation were seen and no post-MRI programming changes were noted. No patient experienced arrhythmia or symptoms during or immediately after MRI. Battery status remained unchanged. No patient experienced post-MRI change in sensing thresholds. Three patients showed no change in the atrial or ventricular pacing thresholds when the pre-MRI values were compared to the immediate post-MRI values and the 3-month follow-up values. All other patients showed a rise or fall of 0.5 V in their chamber threshold values when the pre-MRI, post-MRI, and 3-month follow-up values were compared. More patients showed a fall in their pacing thresholds than a rise post-MRI.

CONCLUSION

While clearly a higher risk group, like nonpacemaker-dependent patients, MRI might be performed in pacemaker-dependent patients if appropriate pacemaker reprogramming, patient monitoring, and MRI scanning techniques are implemented.

Safe scanning, but frequent artifacts mimicking bradycardia and tachycardia during magnetic resonance imaging (MRI) in patients with an implantable loop recorder (ILR)

BACKGROUND

Patients with implantable devices are generally not permitted to undergo magnetic resonance imaging (MRI) because of potentially deleterious interactions. Little has been reported regarding the safety and effects of MRI scanning of patients with implantable loop recorders (ILRs). We evaluated the safety of scanning patients with ILRs and the output of the ILR after undergoing MRI.

METHODS

Ten patients underwent 11 MRI scanning events. All patients had Reveal Plus (Medtronic, Minneapolis, MN) ILRs. Seven cranial, two lumbar-spine, one shoulder, and one knee MRI were performed. All of the MRIs were performed with the understanding that the patient had an ILR. In each patient, the ILR was cleared moments before the scan and the integrity of the signal and time date stamp were verified. The devices were reinterrogated immediately after MRI in 10 patients and two days post MR scanning in one patient. Each patient was questioned post MRI regarding any symptoms experienced during the scan.

RESULTS

Both tachy and bradyarrhythmias appeared as artifacts as a result of ILR exposure to MRI. Post MRI, none of the ILRs showed diminished signal integrity, altered programmed parameters, diminished battery status, inability to communicate or be reprogrammed. No sensations of tugging or warmth at the implant site were noted.

CONCLUSION

MRI was performed in ILR patients without harm to the patient or permanent damage to the ILR. MRI scanning of the Reveal appears safe. Artifact mimicking an arrhythmia was common, however, and must be excluded in any ILR patient undergoing MRI to avoid mistakenly attributing a syncopal episode, or palpitations to the artifacts produced from MRI exposure.

Strategy for Safe Performance of Magnetic Resonance Imaging on a Patient with Implantable Cardioverter Defibrillator

Clinically indicated magnetic resonance imaging (MRI) of the brain was safely performed at 1.5 T on a patient with an implantable cardioverter defibrillator (ICD). The ICD was reprogrammed to detection only, and imaging hardware and protocols were modified to minimize radiofrequency power deposition to the ICD system. The integrity of the ICD system was verified immediately post-MRI and after 6 weeks, including an ICD test with induction of ventricular fibrillation. This case demonstrates that in exceptional circumstances, in carefully selected patients, and using special precautions, an MRI exam of the brain may be possible in patients with ICDs.

Interference of programmed electromagnetic stimulation with pacemakers and automatic implantable cardioverter defibrillators

A commercially available magnetic therapy system, designed for clinical application as well as for private use without medical supervision, was examined with respect to its potential for causing electromagnetic interference with implantable pacemakers (PMs) and automatic implantable cardioverter defibrillators (AICDs). A sample of 15 PMs and 5 AICDs were experimentally investigated. Each of the implants was realistically positioned in a homogeneous, electrically passive torso phantom and exposed to the magnetic fields of the system's applicators (whole body mat, cushion, and bar applicator). The detection thresholds of the implants were programmed to maximum sensitivity and both unipolar as well as bipolar electrode configurations were considered. The evaluation of possible interferences was derived from the internal event storages and pacing statistics recorded by the implants during exposure. Any "heart activity" recorded by the implants during exposure was interpreted as a potential interference, because the implant obviously misinterpreted the external interference signal as a physiological signal. Only cases without any recorded "heart activity" and with nominal pacing rates (as expected from the program parameter settings) of the implants were rated as "interference-free." Exposure to the whole body mat (peak magnetic induction up to 265 microT) did not show an influence on PMs and AICD in any case. The cushion applicator at the highest field intensity (peak magnetic induction up to 360 microT) led to atrial sensing defects in four PM models with unipolar electrode configuration. Under bipolar electrode configuration no disturbances occurred. The bar applicator led to sensing problems and consecutively reduced pacing rates in all tested PM models under unipolar electrode configuration and maximum field intensity (peak magnetic induction up to 980 microT). Bipolar electrode configuration resolved the problem. The investigated AICDs did not show malfunctions under any investigated condition. In conclusion, the examined PEMF therapy system did not interfere with the investigated implantable cardiac devices with bipolar electrode configuration. However, unipolar electrode configuration in pacemakers seems to be potentially hazardous during application of the examined PEMF therapy system.

MRI induced heating of pacemaker leads: effect of temperature probe positioning and pacemaker placement on lead tip heating and local SAR

The radio frequency field used in magnetic resonance imaging (MRI) procedures leads to temperature and local absorption rate (SAR) increase for patients with implanted pacemakers (PM). In this work a methodological approach for temperature and SAR measurements using fluoroptic probes is presented. Experimental measures show how the position of temperature probes affects the temperature and SAR value measured at the lead tip. The transversal contact between the active portion of the probe and the lead tip is the configuration associated with the highest values for temperature and SAR, whereas other configurations may lead to an underestimation close to 11% and 70% for temperature and SAR, respectively. In addition measurements were performed on a human-shaped phantom inside a real MRI system, in order to investigate the effect of the PM placement and of the lead geometry on heating and local SAR.

Influence of electromagnetic interference on implanted cardiac arrhythmia devices in and around a magnetically levitated linear motor car

This study was designed to determine the susceptibility of implanted cardiac arrhythmia devices to electromagnetic interference in and around a magnetically levitated linear motor car [High-Speed Surface Transport (HSST)]. During the study, cardiac devices were connected to a phantom model that had similar characteristics to the human body. Three pacemakers from three manufacturers and one implantable cardioverter-defibrillator (ICD) were evaluated in and around the magnetically levitated vehicle. The system is based on a normal conductive system levitated by the attractive force of magnets and propelled by a linear induction motor without wheels. The magnetic field strength at 40 cm from the vehicle in the nonlevitating state was 0.12 mT and that during levitation was 0.20 mT. The magnetic and electric field strengths on a seat close to the variable voltage/variable frequency inverter while the vehicle was moving and at rest were 0.13 mT, 2.95 V/m and 0.04 mT, 0.36 V/m, respectively. Data recorded on a seat close to the reactor while the vehicle was moving and at rest were 0.09 mT, 2.45 V/m and 0.05 mT, 1.46 V/m, respectively. Measured magnetic and electric field strengths both inside and outside the linear motor car were too low to result in device inactivation. No sensing, pacing, or arrhythmic interactions were noted with any pacemaker or ICD programmed in either bipolar and unipolar configurations. In conclusion, our data suggest that a permanent programming change or a device failure is unlikely to occur and that the linear motor car system is probably safe for patients with one of the four implanted cardiac arrhythmia devices used in this study under the conditions tested.

Cardiac magnetic resonance imaging in a patient with implantable cardioverter-defibrillator

The presence of pacemakers and implantable cardioverter-defibrillators (ICD) is considered historically a contraindication to magnetic resonance (MR) imaging. This image modality has unparalleled soft-tissue imaging capabilities, and many consider it as the image of choice for patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C). ICDs are now smaller, with less magnetic materials and improved electromagnetic interference protection. We tested modern ICDs for heat, force, function and image distortion and found that several of them may indeed be MRI safe. We report here a patient who was suspected of ARVD/C, underwent ICD implantation based on MR safety testing, and underwent intentionally scheduled follow-up cardiac MR imaging. This is the description of a patient with an ICD who had planned MRI scanning. The scan was safe and most of the MRI images were of high quality.

Far-Field R-Wave Reduction with a Novel Lead Design: Experimental and Human Results

INTRODUCTION

The purpose of this study was to examine a bipolar screw-in lead (NL), specially designed to reduce unwanted far-field R-wave (FFRW) signal detection in an acute human setting. The results were compared with animal experiments.

METHODS

The newly designed lead with a center-to-center distance between the anode and cathode electrodes of 3.23 mm, corresponding to an inter-electrode spacing of 1.1 mm was implanted in nine canines with a follow-up of 6 months. Sensing of P waves, FFRW signals, pacing threshold, and impedance was measured at regular intervals. As a result of the positive outcome with the animal study, an acute human experiment was performed. In patients scheduled for conventional dual chamber pacemaker implantation, the NL was compared to a Tendril Model 1388T bipolar screw-in lead (St. Jude Medical, CRMD, Sylmar, CA).

RESULTS

Utilizing a tip-to-ring distance of 1.1 mm, the optimum P wave to FFRW ratio was found in animal experiments. In the acute human tests in 15 patients, the mean P-wave voltage of the 1388T lead of 3.30 +/- 1.54 mV was slightly larger than that of the NL, at 2.55 +/- 1.11 mV, but did not differ significantly (P = 0.13). The FFRW voltage of the 1388T lead was 0.62 +/- 0.37 mV and was significantly greater from that of the NL, at 0.10 +/- 0.08 mV (P < 0.0001). Pacing thresholds and pacing impedances were comparable.

CONCLUSION

Animal testing results were reproducible in the acute human test setting. The lead reduced the paced FFRW signal amplitudes significantly, allowing for high atrial sensitivity settings but without sensing the FFRW. A robust P-wave signal could be retained.

Cardiac dyssynchrony analysis using circumferential versus longitudinal strain: implications for assessing cardiac resynchronization

BACKGROUND

QRS duration is commonly used to select heart failure patients for cardiac resynchronization therapy (CRT). However, not all patients respond to CRT, and recent data suggest that direct assessments of mechanical dyssynchrony may better predict chronic response. Echo-Doppler methods are being used increasingly, but these principally rely on longitudinal motion (epsilonll). It is unknown whether this analysis yields qualitative and/or quantitative results similar to those based on motion in the predominant muscle-fiber orientation (circumferential; epsiloncc).

METHODS AND RESULTS

Both epsilonll and epsiloncc strains were calculated throughout the left ventricle from 3D MR-tagged images for the full cardiac cycle in dogs with cardiac failure and a left bundle conduction delay. Dyssynchrony was assessed from both temporal and regional strain variance analysis. CRT implemented by either biventricular (BiV) or left ventricular-only (LV) pacing enhanced systolic function similarly and correlated with improved dyssynchrony based on epsiloncc-based metrics. In contrast, longitudinal-based analyses revealed significant resynchronization with BiV but not LV for the overall cycle and correlated poorly with global functional benefit. Furthermore, unlike circumferential analysis, epsilonll-based indexes indicated resynchronization in diastole but much less in systole and had a lower dynamic range and higher intrasubject variance.

CONCLUSIONS

Dyssynchrony assessed by longitudinal motion is less sensitive to dyssynchrony, follows different time courses than those from circumferential motion, and may manifest CRT benefit during specific cardiac phases depending on pacing mode. These results highlight potential limitations to epsilonll-based analyses and support further efforts to develop noninvasive synchrony measures based on circumferential deformation.

Safe Performance of Magnetic Resonance Imaging on a Patient with an ICD

This is a report on a patient with an implanted cardioverter defibrillator (ICD) who intentionally underwent magnetic resonance imaging (MRI) of a malignant brain tumor. To avoid inadequate detection of ventricular tachycardia (VT) or ventricular fibrillation (VF), the ICD was inactivated by programming the VT-detection and VT/VF-therapy status off. The patient came through the protocol safely and without any difficulty or discomfort. There was no arrhythmic event. MRI affected neither programmed data nor the function of the ICD system.

Electrosurgery after Cochlear Implantation: Eighth Nerve Electrophysiology

HYPOTHESIS

Monopolar electrosurgery below the neck in cochlear implant recipients can be performed without damage to the internal cochlear stimulator, electrode array, and the cochlear nerve.

STUDY DESIGN

Prospective pre- and postintervention electrically evoked compound action potential (ECAP) study of cochlear nerve function and behavioral sound perception assessment.

METHODS

Neural response telemetry (NRT) was used to measure ECAPs before and after the use of monopolar electrosurgery during coronary artery bypass surgery to assess prosthetic device function and electrophysiologic function of the cochlear nerve. In addition, electrode voltage impedances and behavioral sound perception was measured at the same time intervals.

RESULTS

ECAPs, behavioral sound perception, and electrode voltage impedances were within the normal range, within compliance, and similar preoperatively and on postoperative day 6.

CONCLUSION

The studies reported herein were a series of measurements designed to test neural integrity and prosthetic device function before and after the use of monopolar electrosurgery. With appropriate precautions, use of monopolar electrosurgery below the neck in cochlear implant recipients can be performed safely.

Electromagnetic interference in cardiac rhythm management devices

Clinicians caring for cardiac device patients with implanted pacemakers or cardioverter defibrillators (ICDs) are frequently asked questions by their patients concerning electromagnetic interference (EMI) sources and the devices. EMI may be radiated or conducted and may be present in many different forms including (but not limited to) radiofrequency waves, microwaves, ionizing radiation, acoustic radiation, static and pulsed magnetic fields, and electric currents. Manufacturers have done an exemplary job of interference protection with device features such as titanium casing, signal filtering, interference rejection circuits, feedthrough capacitors, noise reversion function, and programmable parameters. Nevertheless, EMI remains a real concern and a potential danger. Many factors influence EMI including those which the patient can regulate (eg, distance from and duration of exposure) and some the patient cannot control (eg, intensity of the EMI field, signal frequency). Potential device responses are many and range from simple temporary oversensing to permanent device damage Several of the more common EMI-generating devices and their likely effects on cardiac devices are considered in the medical, home, and daily living and work environments.

Modern pacemaker and implantable cardioverter/defibrillator systems can be magnetic resonance imaging safe: in vitro and in vivo assessment of safety and function at 1.5 T

BACKGROUND

MRI has unparalleled soft-tissue imaging capabilities. The presence of devices such as pacemakers and implantable cardioverter/defibrillators (ICDs), however, is historically considered a contraindication to MRI. These devices are now smaller, with less magnetic material and improved electromagnetic interference protection. Our aim was to determine whether these modern systems can be used in an MR environment.

METHODS AND RESULTS

We tested in vitro and in vivo lead heating, device function, force acting on the device, and image distortion at 1.5 T. Clinical MR protocols and in vivo measurements yielded temperature changes <0.5 degrees C. Older (manufactured before 2000) ICDs were damaged by the MR scans. Newer ICD systems and most pacemakers, however, were not. The maximal force acting on newer devices was <100 g. Modern (manufactured after 2000) ICD systems were implanted in dogs (n=18), and after 4 weeks, 3- to 4-hour MR scans were performed (n=15). No device dysfunction occurred. The images were of high quality with distortion dependent on the scan sequence and plane. Pacing threshold and intracardiac electrogram amplitude were unchanged over the 8 weeks, except in 1 animal that, after MRI, had a transient (<12 hours) capture failure. Pathological data of the scanned animals revealed very limited necrosis or fibrosis at the tip of the lead area, which was not different from controls (n=3) not subjected to MRI.

CONCLUSIONS

These data suggest that certain modern pacemaker and ICD systems may indeed be MRI safe. This may have major clinical implications for current imaging practices.

Assessment and management of patients with pacemakers and implantable cardioverter defibrillators

OBJECTIVE

To review the design and function of pacemakers and implantable cardioverter defibrillators with particular attention to those aspects that are of clinical relevance to perioperative and critical care physicians.

MAIN POINTS

Pacemakers and implantable cardioverter defibrillators are complex devices that interact with cardiac function in ways that can significantly influence hemodynamics. A basic appreciation of device technology is essential to understanding both the normal patterns of pacemaker and implantable cardioverter defibrillator usage and the ways in which iatrogenic influences may result in adverse outcomes. The most important concern for pacemaker patients who enter the hospital is exposure to electromagnetic interference. Exposure is mainly from surgical cautery, but other sources are also present. With awareness of these concerns and an understanding of how to prevent adverse interactions, it is possible to safely care for these patients in the critical care setting. Despite recommended precautions, undesirable outcomes may occur and the clinician must be prepared to intervene in an appropriate manner to prevent patient injury.