Use Caution When Applying Magnets to Pacemakers or Defibrillators for Surgery

Schulman, Peter M. MD*; Rozner, Marc A. PhD, MD

Anesthesia & Analgesia:
doi: 10.1213/ANE.0b013e31829003a1
Patient Safety: Case Report

The application of a magnet to a pacemaker (intended to cause asynchronous pacing) or implanted cardioverter defibrillator (intended to prevent shocks) during surgery without a clear understanding of actual magnet function(s) or precautions can have unexpected, untoward, or harmful consequences. In this report, we present 3 cases in which inadequate assessment of cardiac implanted electronic device (CIED) function, coupled with magnet application, contributed to or resulted in inappropriate antitachycardia pacing or shocks, CIED damage, or patient injury. Although these cases might be rare, they reinforce the need for a timely, detailed preoperative review of CIED function and programming as recommended by the American Society of Anesthesiologists and the Heart Rhythm Society.

In Brief

Published ahead of print June 11, 2013.

Author Information

From the *Department of Anesthesiology & Perioperative Medicine, Oregon Health and Science University, Portland, Oregon; and Department of Anesthesiology and Perioperative Medicine, Department of Cardiology, University of Texas MD Anderson Cancer Center, Houston, Texas.

Accepted for publication February 11, 2013

Published ahead of print June 11, 2013.

Funding: No funding source.

Conflict of Interest: See Disclosures at the end of the article.

This report will be presented, in part, at the American Society of Anesthesiologists, Washington, DC 2012.

Reprints will not be available from the authors.

Address correspondence to Marc A. Rozner, PhD, MD, Department of Anesthesiology and Perioperative Medicine, University of Texas MD Anderson Cancer Center, 1400 Holcombe Blvd., Mail Code 0409. Houston, TX 77030. Address e-mail to

Article Outline

In describing recommendations for the perioperative management of a patient with a cardiac implantable electronic device (CIED), several published documents suggest that a magnet can safely be applied to a cardiac pacemaker (PM) to invoke asynchronous pacing or to an implantable cardioverter defibrillator (ICD) to disable antitachycardia therapies.1–3 However, placing a magnet over a PM or ICD can have unexpected or untoward effects, and several authors have cautioned against substituting magnet application for individualized treatment. Rasmussen et al.4 reported 4 cases wherein magnet application permanently deactivated antitachycardia therapy in Guidant (BOS-GDT, Boston Scientific, Natick, MA) ICDs, but subsequent programmer software revision now mostly prevents this problem. Allen5 raised the issue that magnet application can have very different effects due to programming, even when applied to different patients with apparently identical devices. Porres et al.6 postoperatively identified an ICD that had gone to battery end-of-life during surgery and attributed it to magnet placement. Although Stone and Apinis7 describe magnet use as “safe and reliable,” subsequently Stone et al.8 warned that “blind” magnet application might fail to address all necessary perioperative issues.

Herein, we present 3 cases from 3 different institutions in which inadequate preoperative assessment of CIED function, coupled with erroneous assumptions about the effects of magnet application, appear to have contributed to or caused inappropriate ICD therapy, CIED damage, or patient injury. Although both the American Society of Anesthesiologists (ASA) and Heart Rhythm Society (HRS) advise either obtaining a timely preoperative interrogation or obtaining knowledge of device functionality and magnet effects, these recommendations were not followed. These cases should serve to caution clinicians involved in the care of CIED patients about the importance of routine and timely preoperative CIED assessment, and the potential hazards of indiscriminate magnet use without knowledge or verification of their true effects.

Because these cases are single events, retrospectively reviewed, without aggregated data, and devoid of “protected health information,” specific written IRB approval is not required.

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Case Description
Case 1

A 33-year-old, 69-kg man with third-degree heart block and recurrent pericardial effusion presented for elective pericardial window without preoperative evaluation of his dual-chamber PM. He was an ambulatory outpatient with mild dyspnea, but significant orthopnea, having undergone previous pericardiocenteses. The cardiologist’s note several days earlier recommended operative pericardial window and percutaneous coronary artery stent intervention for “80% left anterior descending lesion” if symptoms (New York Heart Association 2) did not improve. The anesthesiologist’s note indicated the absence of a preoperative PM evaluation. The PM brand, model, settings, and implant date (BOS-GDT, Insignia, dual mode, dual chamber, dual sensing, 2 years earlier) along with his chemotherapy exposure (mustard, vincristine, procarbazine, doxorubicin, bleomycin, vinblastine, and dacarbazine for lymphoma approximately 20 years earlier) were not present in the anesthesiology notes.

Initially, he had sinus rhythm, 75 to 80 bpm, with ventricular pacing that was tracking his atrial function and producing atrioventricular (AV) synchrony (called P-wave synchronous ventricular pacing). He underwent arterial line placement, then awake fiberoptic intubation in the sitting position using 2-mg midazolam and 100-μg (total) fentanyl to preserve spontaneous respiration and maintain hemodynamics. On administration of 20-mg ketamine, his arterial blood pressure decreased. A magnet was applied over the PM, intending to augment cardiac output by increasing heart rate from 75 to 100 bpm. As his vital signs deteriorated, cardiopulmonary resuscitation was commenced, quickly followed by emergent minithoracotomy with improvement of conditions. Postoperative review of the electronic anesthetic record and electroencephalogram tracing at magnet application (Fig. 1, A and B) found magnet application, as expected, initiated asynchronous AV pacing at 100 bpm. However, complete failure of atrial capture and ventricular noncapture every other pace (ventricular electrical alternans) effectively converted the previously AV synchronous activity at 75 bpm to ventricular-only pacing at 50 bpm, which appears to have exacerbated the hemodynamic compromise. Postoperative PM check showed the most recent interrogation was 15 months before surgery. The postoperative interrogation also demonstrated new (since the prior interrogation) inadequate atrial and longstanding (known at the prior interrogation) inadequate ventricular pacing outputs relative to pacing threshold in this pacing-dependent patient.

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Case 2

A 70-year-old man with a BOS-GDT H-170 biventricular-ICD presented for median sternotomy and revision of a prior esophagectomy—colonic interposition. His device was implanted 25 months earlier for ischemic cardiomyopathy and to provide cardiac resynchronization therapy. Immediate preoperative interrogation revealed an episode of antitachycardia pacing (ATP) for what appeared to be electrical noise (Fig. 2) approximately 8 months earlier. Investigation revealed that the ATP was delivered during his initial esophageal surgery. Data stored in the ICD indicated an interrogation 13 days before the first surgery, but no interrogation report was in his chart. The anesthesiologist who performed the first case reported that he placed a magnet on the ICD to prevent firing as instructed by the cardiologist. The anesthesiologist was unaware that this ICD likely had a disabled magnet switch in accordance with a manufacturer’s product advisory9 issued 10 months earlier.

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Case 3

A 69-year-old man with a medical history of congestive heart failure status post placement of a BOS-GDT H-175 ICD, coronary artery disease, renal artery stenosis, focal segmental glomerulosclerosis, nephrotic syndrome, chronic obstructive pulmonary disease, and peripheral vascular disease underwent elective thoracoabdominal aortic aneurysm repair in the right lateral position. Proximal extension of the arch aneurysm, discovered after initial dissection, necessitated institution of deep hypothermic circulatory arrest. The ICD was not evaluated preoperatively. The operative team used a magnet to prevent ICD firing, unaware that the magnet mode was disabled due to a manufacturer’s product advisory.9 Electrosurgical dispersive pads were placed on the left buttock and the left medial thigh. After some shocks were noticed by the surgeon and anesthesiologist, the magnet was repositioned because of the belief that it had moved. A postoperative ICD check revealed at least 20 shocks and at least 12 ATP sequences for electrical noise (Fig. 3), resulting in premature battery depletion requiring ICD replacement. The patient also suffered a perioperative cerebrovascular accident.

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Patients with CIEDs sometimes undergo invasive procedures without adequate knowledge of the device or its functionality by their perioperative caring teams. Possible explanations for this behavior include inconvenience, as well as personnel and economic barriers to preoperative CIED interrogation. In each of our 3 cases, 1 or more of these issues, combined with the apparent assumptions that: (1) all devices work properly and (2) magnet placement will confer safe care, appear to have contributed to preventable adverse events and patient injury, such as cardiopulmonary resuscitation or inappropriate high-energy therapy. Several reports,10–14 including a recent, large, randomized trial,15 have highlighted myocardial injury or increased mortality from both appropriate and inappropriate shock. Even ATP has been identified as a cause of myocardial injury16 and increased mortality.15

Commonly held, but incorrect, beliefs about magnet application include the following: (1) magnet application to a conventional PM always produces asynchronous pacing; (2) asynchronous pacing is safe and effective under all circumstances; and (3) all ICDs suspend antitachycardia therapy with magnet application. However, application of a magnet over a CIED can have unpredictable or unreliable effects (Table 1).2,17,18

Both the ASA19 and HRS1 recommend preoperative collection of CIED programmed variables. The ASA further recommends preoperative CIED evaluation and caution with magnet use. In case 1, magnet application did indeed produce asynchronous pacing. However, it caused acute loss of AV synchrony, because atrial pacing never depolarized the atrium, ventricular pacing depolarized the ventricle only 50% of the time, and the patient’s complete heart block prevented native ventricular depolarization. Although this patient had tamponade physiology and received positive pressure ventilation, the loss of atrial transport caused by magnet application likely further compromised the worsening hemodynamics. In cases 2 (BOS-GDT H-170) and 3 (BOS-GDT H-175), knowledge of the BOS-GDT ICD tone functions could have allowed determination that magnet placement did not disable antitachycardia therapy. Although both of these ICDs will emit tones on magnet placement to indicate the presence of a magnet and status of antitachycardia therapy, neither record has documentation suggesting that tones were sought or that auscultation of the device was performed. In both instances, the magnet switch had been disabled in response to a product advisory,20 and no tones would have been emitted, alerting the anesthesiologists that ICD antitachycardia therapies were still active. In case 3, the failure of the operative personnel to reliably observe movement during shocks likely reflects use of muscle relaxants and the incomplete operative view of the heart in the right lateral position.

Since the publication of the report “To Err is Human” by the Institute of Medicine21 more than 10 years ago, Landrigan et al.22 posited that no significant improvement has occurred despite considerable effort and dollars expended. Parry et al.23 recently suggested using “morbidity and mortality reviews, executive walk-rounds, root-cause analyses, and failure modes and effects analyses” to identify clues for improving hazardous systems. However, these efforts will detect only known causes of harm. We believe that our 3 cases represent “occult harm,” as identifying all of the contributing factors in these cases remains quite difficult. In case 1, we believe that inappropriate PM programming (inadequate pacing outputs) and the acute loss of AV synchrony with magnet placement worsened the clinical situation. In cases 2 and 3, both patients received inappropriate antitachycardia therapy (ATP and/or shock), both of which appear to shorten patients’ lives.15 At this time, it is impossible to know whether the multiple shocks in case 3 contributed to the patient’s stroke.

Except for true surgical emergencies, clinicians caring for these patients should ensure appropriate device function preoperatively, either through contact with the patient’s CIED physician/clinic (as recommended by HRS) or a de novo interrogation (as recommended by ASA). For planned intraoperative magnet use, a full understanding and verification of magnet function before proceeding to the operating room seems indicated. Collaboration by the CIED manufacturers to consider standardizing the response to magnet placement24 would likely be a useful additional step towards minimizing risk. For several years, the Association for the Advancement of Medical Instrumentation (Fairfax, VA) has been attempting to create a “universal magnet mode response,” but at this time, no such development has taken place.

In hospital, electromagnetic interference (EMI)-induced shocks might be a significant issue in ICD patients. A review of 2000 randomly selected telephonic records after 1 or more shocks between 2001 and 2008 showed 5248 shocks, 1570 (30%) of which were inappropriate, and that 76 of these 1570 (4.8%) were due to EMI.25 These cases, in which EMI appears on multiple leads, EMI is isolated to only 1 day with a narrow time window, and EMI stops around the time of the therapy should be suspicious for in-hospital occurrence. We believe that inappropriate antitachycardia therapy owing to EMI within a hospital environment should become a reportable event to the United States Food and Drug Administration or the Joint Commission, as it represents potential patient injury.

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Name: Peter M. Schulman, MD.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript. Dr. Schulman wrote many of the revisions.

Attestation: Peter M. Schulman approved the final manuscript.

Conflicts of Interest: Peter M. Schulman received research funding from Boston Scientific. The grant funding from Boston Scientific is unrelated to the case report herein.

Name: Marc A. Rozner, PhD, MD.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript. Dr. Rozner wrote many of the revisions.

Attestation: Marc A. Rozner approved the final manuscript.

Conflicts of Interest: The author has no conflicts of interest to declare.

This manuscript was handled by: Sorin J. Brull, MD.

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