856 Unintentional Deactivation of ICDs Mayo Clin Proc, August 2002, Vol 77 Figure 1. Case 3. Printout from Guidant programmer (Guidant Corp, St Paul,

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1 Mayo Clin Proc, August 2002, Vol 77 Unintentional Deactivation of ICDs 855 Case Report Unintentional Deactivation of Implantable Cardioverter-Defibrillators in Health Care Settings MARY JANE RASMUSSEN, RN; PAUL A. FRIEDMAN, MD; STEPHEN C. HAMMILL, MD; AND ROBERT F. REA, MD Patients with implanted pacemakers and defibrillators are routinely cautioned regarding exposure to environmental magnetic fields because such exposure may interfere with device function. Previous reports have confirmed interference with bingo wands, stereo speakers, and various workplace sources. In the 4 patients in this report, we document inadvertent alteration of the tachyarrhythmia detection function of implantable cardioverter-defibrillators (ICDs) that occurred in health care settings because of deliberately applied magnetic fields. Three of these patients had pectorally implanted ICDs that may have been confused with pacemakers, and 2 patients had undergone office surgical procedures at which time a magnet had been applied over the device. These events stemmed from (1) potential confusion by health care workers about the nature of the implanted device and (2) unique features in a specific manufacturer s defibrillator. We recommend the following steps to avoid such problems: (1) when device programming hardware and trained personnel are readily available, the patient s device should be interrogated and reprogrammed before and after any procedure involving electrocautery; (2) patients with ICDs should be monitored during device inactivation because they are unprotected from potentially life-threatening arrhythmias during this period; and (3) if the clinical situation does not allow device interrogation and reprogramming, the patient should be monitored electrocardiographically during magnet application and the device interrogated as soon as possible after magnet removal. Mayo Clin Proc. 2002;77: ECG = electrocardiogram; ICD = implantable cardioverterdefibrillator From the Guidant Corporation, St Paul, Minn (M.J.R.); and the Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic, Rochester, Minn (P.A.F., S.C.H., R.F.R.). Address reprint requests and correspondence to Robert F. Rea, MD, Division of Cardiovascular Diseases, Mayo Clinic, 200 First St SW, Rochester, MN ( rfrea@mayo.edu). Patients who receive implantable pacemakers and implantable cardioverter-defibrillators (ICDs) are routinely cautioned to avoid exposure to magnetic fields because such exposure can temporarily affect device function or, less commonly, reprogram the device. Environmental sources of such electromagnetic interference include portable electric tools, certain engine parts (alternators), and magnets in games and science sets. In many hospital and outpatient settings, deliberate magnet application over a pacemaker pulse generator is performed routinely to assess battery status or pacemaker function. During recording of the electrocardiogram (ECG), standard practice is to obtain an ECG with and without magnet for this purpose. In addition, in clinical settings in which electrocautery might be used (major or minor surgery), continuous application of a magnet over the pacemaker inhibits sensing of cardiac or noncardiac electrical events causing the pacemaker to revert to fixedrate pacing. This protects the patient from inappropriate inhibition of pacer output and inappropriate tracking of sensed electrical signal events during electrocautery procedures. We describe 4 patients who were referred for evaluation of ICD function in whom magnet application over ICD pulse generators in health care settings altered device function and, in 1 instance, inhibited potentially lifesaving automatic defibrillation. This outcome likely resulted from confusion about the behavior of pacemakers and ICDs with magnet application. Key differences between the magnet response of ICDs and pacemakers are emphasized. METHODS Three of the cases in this report were obtained from a device clinic that monitors approximately 500 patients with ICDs; 1 patient was referred from an institution elsewhere specifically for ICD evaluation. The cases were identified over approximately a 2-year period. In 2 of the patients, detailed medical records from the Mayo Clinic in Rochester, Minn, were available for review; in the other 2 patients, magnet application occurred in clinical settings at institutions elsewhere. In all patients device interrogation indicated that the tachyarrhythmia detection had been altered by a magnet. Mayo Clin Proc. 2002;77: Mayo Foundation for Medical Education and Research

2 856 Unintentional Deactivation of ICDs Mayo Clin Proc, August 2002, Vol 77 Figure 1. Case 3. Printout from Guidant programmer (Guidant Corp, St Paul, Minn) indicating deactivation of implantable cardioverter-defibrillator by magnet. REPORT OF CASES Case 1 A 76-year-old man had an abdominally placed ICD (model 1746, Guidant Corp, St Paul, Minn) and was monitored at a facility elsewhere. He underwent ICD evaluation as part of a preoperative examination at Mayo Clinic, Rochester, Minn, in June 1998, with the intent to inhibit sensing temporarily during the planned surgery. Interrogation showed that the tachy mode had been changed with a magnet on February 27, At that time, the patient had undergone an outpatient surgical procedure at a facility elsewhere and recalled having a magnet applied over his ICD. Case 2 A 61-year-old man with an ICD (model 1743, Guidant Corp) placed pectorally underwent routine ICD follow-up at Mayo Clinic in Rochester in May Interrogation showed that the tachy mode had been changed with a magnet on November 19, Medical chart review showed that the patient had undergone excision of a skin lesion with application of electrocautery on that date. The patient recalled having had a magnet applied to his ICD at the time of the procedure. Routine interrogation in November 1997 showed that the device had been programmed to monitor + therapy with the change tachy mode with magnet feature enabled. Case 3 A 61-year-old man with an ICD (model 1743, Guidant Corp) placed pectorally died while sleeping. Postmortem interrogation of the ICD revealed that the tachycardia detection had been disabled with a magnet 3 months before his death, when he had been evaluated at an emergency department elsewhere (Figure 1). At device interrogation at the Mayo Clinic in Rochester 4 months before his death, tachycardia detection had been active and the change tachy mode with magnet feature enabled. The coincidence of the date of inactivation and the date of the patient s evaluation at the hospital elsewhere indicates that magnet application at that time had deactivated the device. Case 4 A 78-year-old man with an ICD (model 1740, Guidant Corp) placed pectorally was admitted for congestive heart failure. At the time of a bradycardic event in the intensive care unit at a referring hospital, an attempt was made to increase the pacing rate with application of a magnet over the device. After transfer to the Mayo Clinic in Rochester, device interrogation showed that the tachy mode had been changed with a magnet and that the tachyarrhythmia detection was inactive. DISCUSSION In these 4 patients, ICD function was altered inadvertently by exposure to magnetic fields in health care settings. All devices were made by a single manufacturer and incorporated a programmable feature that allows alteration of device function with application of a magnet over the device canister. In 1 patient, potentially life-saving defibrillator therapy was disabled. This report highlights the need for full interrogation and programming of devices before and after procedures involving electrocautery and the limited situations in which magnet application over ICDs is appropriate. Inadvertent ICD deactivation by magnetic fields has been reported previously with devices such as bingo wands, 1 stereo speakers, 2 and workplace environments. 3 As shown in the current series, deliberate exposure to magnetic fields may occur in health care settings when ICDs are confused with antibradycardia pacing systems with respect to their behavior with magnet application. This confusion may be due to similarities of size, shape, and implant location as well as the increasingly sophisticated pacemaker functions of ICDs. Magnet application over a pacemaker closes a reed switch that changes the pacemaker to an asynchronous

3 Mayo Clin Proc, August 2002, Vol 77 Unintentional Deactivation of ICDs 857 Figure 2. Programmer screen for implantable cardioverter-defibrillator (Guidant Corp, St Paul, Minn) showing options for magnet use. Note that Enable Magnet Use allows temporary inhibition of tachyarrhythmia sensing and must be distinguished from Change Tachy Mode with Magnet. EGM = electrogram; ERI = elective replacement index. mode (VOO, DOO, AOO). This provides information about residual battery life (so-called magnet rate) and allows electrocautery to be used without concern about altering pacing function. In many (but not all) pacemakers, magnet rates are typically greater than programmed lower rates. In many pacemakers application of a magnet can increase the pacing rate promptly, as in case 4. Magnet application over ICD pulse generators alters the pacing rate only in devices made by ELA Medical LLC (Plymouth, Minn). In these ICDs, application of a magnet causes pacing in the DDD mode at 96 beats/min. In all ICDs, magnet application temporarily inhibits all therapy delivery and detection of arrhythmias or electrical noise, which is necessary to avoid delivery of shocks during electrocautery. In devices made by Guidant Corp, the cardioverter-defibrillator functions of the device can be inactivated by a magnet applied for 30 seconds if the change tachy mode with magnet feature is programmed on (Figures 1 and 2). Reprogramming by trained personnel or reapplication of a magnet for 30 seconds is then necessary to reactivate the defibrillator functions of the device. Device inactivation by a magnet is indicated by emission of a continuous tone during application. Reactivation is indicated by emission of R- wave synchronous beeps from the device while the magnet is applied. Medtronic Inc (Bloomington, Minn) recently released a device for temporary inhibition of its defibrillators that incorporates telemetry and light-emitting diodes to indicate that device detection is inhibited. However, such a device would not recognize other manufacturers devices, although the generated magnetic field could alter device function as any magnetic field might. In a recent survey 4 of cutaneous surgeons regarding precautions and complications in the use of electrosurgery in patients with pacemakers and defibrillators, only 15% of respondents reported routine deactivation of ICDs before procedures. The most commonly employed precautions were the use of brief bursts of energy at low power and avoidance of application in proximity to implanted devices. Twenty-five complications were reported, including 4 ICD discharges. 4 Medical personnel in a wide variety of clinical arenas should be cognizant of the differences between ICDs and pacemaker systems and the different behavior of these devices with magnet application (Table 1). Patients themselves may equate defibrillators with pacemakers despite educational efforts. Hence, relying on history alone may be insufficient. When a patient cannot provide a clearly accurate medical history or an identification card for the device, chest radiography can easily distinguish between the 2 devices. Both systems may have leads in the atrium and ventricle, and both may be placed in the upper chest area. Pacemaker leads have very small electrodes near the distal end of the leads (Figure 3, left and right). However, ICD leads have large coil electrodes in the right

4 858 Unintentional Deactivation of ICDs Mayo Clin Proc, August 2002, Vol 77 Table 1. Effects of Magnet Application on Pacemakers and ICDs* Function Pacemaker Defibrillator Pacing Reverts to asynchronous pacing (increased rate in some Unaffected except in ELA Medical LLC (Plymouth, Minn) devices, which pace devices with decrement in output in first 3 beats DDD at 96 beats/min [threshold margin test]) Sensing Inhibited. Pacemaker will not be inhibited or triggered Tachyarrhythmia sensing and therapy inhibited; bradyarrhythmia sensing by environmental electrical signals unaffected. Pacemaker function of ICD may be inhibited or triggered by environmental electrical signals. In Guidant Corp (St Paul, Minn) devices, with change tachy mode with magnet enabled (Figure 2), 30 seconds of application turns tachyarrhythmia sensing off until device is reprogrammed (or magnet reapplied for 30 seconds) *ICD = implantable cardioverter-defibrillator. ventricle and, in some systems, in the right atrium and superior vena cava (Figure 4, left and right). Magnet application over all ICD pulse generators will inhibit sensing and antitachycardia therapy during the period of magnet application. However, it is important to interrogate the device after the procedure to confirm that sensing and antitachycardia therapies are active. Our early practice had been to activate the change tachy mode with magnet feature to allow remote referring facilities without ready access to ICD programmers to turn devices off in the event of frequent inappropriate shocks due to atrial fibrillation or patient or family request, eg, terminal illness in a patient with advance directives. As a result of the current observations and increased availability of programmers and industry support personnel, we do not enable the change tachy mode with magnet feature in any Guidant ICDs. (Of note, in the default programming of these devices, this feature is disabled.) When programmed in such a manner, device deactivation requires use of a programmer and trained personnel. Additionally, we have notified hospital departments where magnet application might occur to query patients closely about their devices and contact us for device management. Health care workers should be alert to the important differences between ICDs and pacemakers and consider the following guidelines. 1. When device programming hardware and trained personnel are readily available, the patient s device should be interrogated before and after any procedure involving electrocautery or magnet application. Figure 3. Posteroanterior (left) and lateral (right) chest radiographs showing pacemaker pulse generator and leads. Small arrowhead indicates atrial pacing lead. Large arrowhead indicates ventricular pacing lead.

5 Mayo Clin Proc, August 2002, Vol 77 Unintentional Deactivation of ICDs 859 Figure 4. Posteroanterior (left) and lateral (right) chest radiographs showing implantable cardioverter-defibrillator pulse generator and leads. Small arrowhead indicates atrial pacing lead. Large arrowheads indicate defibrillator lead coils in the right atrium and right ventricle. 2. Patients with ICDs should be monitored during device inactivation because they are unprotected from potentially life-threatening arrhythmias during this period. 3. If there is doubt about the nature of the device or the clinical situation does not allow device interrogation before magnet application, the patient should be monitored with use of an ECG during magnet application and the device interrogated after magnet removal. REFERENCES 1. Ferrick KJ, Johnston D, Kim SG, et al. Inadvertent AICD inactivation while playing bingo. Am Heart J. 1991;121(1, pt 1): Bonnet CA, Elson JJ, Fogoros RN. Accidental deactivation of the automatic implantable cardioverter defibrillator. Am Heart J. 1990; 120: Miller K. Case study: implications of the recommendation to the patient with an AICD to avoid magnetic fields. Am J Crit Care. 1993; 2: El-Gamal HM, Dufresne RG, Saddler K. Electrosurgery, pacemakers and ICDs: a survey of precautions and complications experienced by cutaneous surgeons. Dermatol Surg. 2001;27: