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Table of Contents
Year : 2013  |  Volume : 16  |  Issue : 1  |  Page : 54-57
Magnets and implantable cardioverter defibrillators: What's the problem?

1 Clinical Anaesthesiology, Division of Cardiac Anesthesia and Department of Anaesthesiology, Perioperative Medicine and Pain Management, University of Miami Miller School of Medicine, Miami, Florida, USA
2 Clinical Anaesthesiology, Department of Anaesthesiology, Perioperative Medicine and Pain Management, University of Miami Miller School of Medicine, Miami, Florida, USA
3 Department of Anaesthesiology, Perioperative Medicine and Pain Management, University of Miami Miller School of Medicine, Miami, Florida, USA

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Date of Submission13-Jul-2012
Date of Acceptance08-Sep-2012
Date of Web Publication2-Jan-2013


A growing number of surgical patients present to the operating room with implantable cardioverter defibrillators (ICD). Peri-operative care of these patients dictates that ICD function be suspended for many surgical procedures to avoid inappropriate, and possibly harmful, ICD therapy triggered by electromagnetic interference (EMI). An alternative to reprogramming the ICD is the use of a magnet to temporarily suspend its function. However, this approach is not without complications. We report a case where magnet use failed to inhibit ICD sensing of EMI, and a shock was delivered to the patient. Measures to decrease EMI, controversies regarding magnet use, and expert recommendations are discussed.

Keywords: Electromagnetic interference, Implantable cardioverter defibrillators, Magnet position, Inhibition of implantable cardioverter defibrillators therapy

How to cite this article:
Rodriguez-Blanco YF, Souki F, Tamayo E, Candiotti K. Magnets and implantable cardioverter defibrillators: What's the problem?. Ann Card Anaesth 2013;16:54-7

How to cite this URL:
Rodriguez-Blanco YF, Souki F, Tamayo E, Candiotti K. Magnets and implantable cardioverter defibrillators: What's the problem?. Ann Card Anaesth [serial online] 2013 [cited 2021 Oct 16];16:54-7. Available from:

   Introduction Top

Implantable cardioverter defibrillators (ICD) are increasingly encountered in the peri-operative setting. This case report highlights the drawbacks of using a magnet to suspend ICD therapy and elucidates the factors associated with electromagnetic interference (EMI). Failure to follow published expert advisory concerning ICDs may lead to adverse events.

   Case Report Top

A 66-year-old male patient presented for resection of a carcinoma of the left floor of the mouth. The patient's medical history included diabetes, hypertension, and chronic atrial fibrillation. The patient also had a history of coronary artery disease and had undergone-coronary artery revascularization surgery twice in 1986 and 2003. In 2010, the patient underwent cardiac catheterization with 4-vessel stenting and the insertion of an ICD (Fortify VR 1231-40Q St. Jude Medical (Sylmar, CA, USA) with bipolar Durata R leads) following an episode of ventricular tachycardia (VT). The device was programmed for the detection and therapy of VT at 166 beats per minute (bpm) and ventricular fibrillation (VF) at 230 bpm. Prior to the surgery, the patient had a regular follow-up by his cardiologist who cleared him for the operation without any recommendations regarding peri-operative ICD management. On the day of the surgery, the ICD was interrogated by a St. Jude representative who advised simply placing a magnet over the device to disable tachyarrhythmia detection-and, therefore, therapy-during surgery.

In the operating room, and prior to induction of anesthesia, a standard clinical doughnut/ring magnet was secured over the ICD on the left chest with an opsite and adhesive tape. By palpation, proper magnet placement was confirmed over the ICD. In addition to standard monitors, an arterial line was placed. An external defibrillator was made available in the operating room and was connected to the patient. The current return pad of the Bovie, monopolar electrosurgical unit, was placed under the patient's right thigh, (the surgeons initially declined to use a bipolar electrosurgical unit since the ICD was supposedly inactive). Following surgical incision, and during tissue dissection, using the monopolar electrocautery, the ICD delivered a shock that was noticed by a sudden movement of the patient. The ECG revealed bradycardia that resolved without medication. The surgeon was notified to stop Bovie use. The magnet was examined and found to be in place; secured directly over the ICD.

The St. Jude representative was contacted, and a recommendation to confirm the position of the magnet was given. Further, the magnet was replaced with another model (Medtronic 9466) magnet and secured. Of note, the original magnet was strong enough to attach itself to a metal cabinet and could not easily be pulled off. The ICD was interrogated, in the operating room, one hour after the event. Magnet response was normal with 30 counts of response recorded. The ICD had incorrectly registered three episodes of ventricular fibrillation during surgery due to electromagnetic interference (EMI). Examination of the episodes revealed that anti-tachycardia pacing (ATP) was delivered for the first episode and shock therapy was delivered for the third episode. Shock therapy was aborted for first and second episodes due to non-sustained events. Surgery proceeded uneventfully after the surgeon switched to bipolar cauterization. Post-operative workup and cardiac consult determined the patient had no adverse sequelae.

   Discussion Top

In the peri-operative period, the major concern with ICDs is EMI. In this case report, many factors may have contributed to EMI and consequently inappropriate ICD therapy including use of monopolar electrocautery, surgical site proximity to ICD, malposition of current return pad, magnet use, device properties, and imperfect advice from the ICD company representative.

EMI can cause ICD reprogramming, temporary inhibition or triggering of pacing functions, battery depletion, asynchronous pacing, damage to the internal circuitry, and myocardial heat damage leading to a rise in threshold and loss of capture. [1],[2],[3] ICDs may misinterpret noise from EMI as VT or VF and deliver inappropriate defibrillation shocks. [4] While inadvertent ICD therapy during surgery is mostly benign, there is a potential for creating sustained ventricular arrhythmias [5] and sudden patient movement with adverse consequences particularly in intra-ocular or neurologic surgery. [6] In this report, given the known hazards of EMI on the function of ICDs, it was advantageous that the patient received shock therapy since it alerted the medical team to the occurrence of EMI and avoidance of potential permanent harm to the ICD and to the patient.

To decrease the risk of EMI, surgeries performed above the umbilicus or close to the ICD <15 cm 2 , [7] (breast, shoulder, head, neck, or carotid procedures) should be executed with bipolar electrosurgery whenever possible. [5] Bipolar electrosurgery is safer to use and does not cause EMI unless it is applied directly to an ICD or pacemaker. [5],[8] Electrocautery should be used in short, infrequent bursts, with a minimum energy setting. [8] The electrocautery should not be activated before contact with the patient since the electric current may leap through the air and be over sensed by the ICD. [5],[8] The current return pad should be placed such that the electric signal-travelling from the cautery to the current return pad - doesn't cross the pulse generator and leads. During head and neck surgery, the current return pad should be placed on the posterior part of the shoulder opposite the pulse generator. [4] In our report, the return pad was naively placed under the right thigh, it should have been placed under the right shoulder.

Clinical magnets are intended to be placed over an ICD or pacemaker implantation site. [9] Magnet position is important. A magnet properly placed will suspend ICD tachyarrhythmia detection without affecting ICD pacing mode or rate. While some ICDs can be programmed to ignore the presence of a magnet (St. Jude Medical, Boston Scientific (Guidant) [4],[5],[6],[10] , other ICDs lack a confirmatory tone to indicate proper magnet placement (St. Jude, Biotronik). In this patient the, St. Jude's ICD was configured to respond to a magnet. Contrary to other ICD manufacturers, it is recommended that for St. Jude's ICDs the magnet should be placed slightly off-center with the magnet curve over the bottom or top end of the ICD [Figure 1]. [11] While suggested by the company as a cause of a lack of inhibition it is unlikely that this small variation in magnet placement should have resulted in a lack of effectiveness of the magnet. If such small variations in magnet placement could in fact be responsible for the failure of ICD inactivation, then magnet placement should not be considered a viable option. As a note, during the pre-operative consultation with the company representative from St. Jude, no mention was made concerning placing the magnet off-center.
Figure 1: Recommended magnet position over St. Jude implantable cardioverter defibrillators. The magnet should be positioned off-center so that the curve of the "donut" magnet is over the top or bottom end of the device. Improper magnet placement may hinder magnet activation and could lead to undesired delivered therapy11. Copyright© 2011 St. Jude Medical.

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Despite changing the magnet after the patient was shocked, we do not believe that magnet strength was an issue. Standard clinical magnets usually have a strength of ≥90 Gauss, [12] and magnetic fields as low as 10 gauss should inhibit tachycardia therapy when they are in close proximity (<3 cm). [13],[14]

Pre-operative communication between the surgeon, anesthesiologist, and cardiologist regarding nature of surgery and electrosurgical equipment use could have led to better patient care. Recent recommendations have stressed less reliance on the independent opinion of ICD company representatives and adoption of a multidisciplinary approach involving the ICD primary care team. [5]

Magnet use versus reprogramming

Magnet use, while not fully reliable, has the advantage of being convenient, immediately reversible and expedites patient care. Tachyarrhythmia therapy is disabled for the least amount of time, since removing the magnet allows immediate reactivation of the device post-operatively. [4] The risk of human error and failure to re-enable tachycardia therapies after the procedure is minimized. [5]

The risk of EMI and surgical site will determine whether a device requires disabling by reprogramming or magnet application. A magnet may be used if the surgical site is distant from the pulse generator and monopolar electrosurgical unit is not utilized. [3] Surgeries performed superior to the umbilicus are at greater risk of causing EMI when electrosurgical units are used; [2],[5],[7] and hence, require reliable disabling of ICD therapy. If the magnet cannot be continuously monitored (e.g., prone position), the ICD is in the surgical field or magnet response is disabled, then a magnet shouldn't be used. [9] In general, magnets do not change the pacemaker function of ICDs. As a result, patients who are pacemaker-dependent will need to have their devices reprogrammed to an asynchronous pacing mode.

The American Society of Anesthesiologists practice advisory recommends tachyarrhythmia treatment of ICDs be programmed off prior to surgery; this is intended for maximum patient safety. During emergent situations, or when reprogramming is not available, a clinical magnet could be applied and secured. On the other hand, the Heart Rhythm Society has no objection to the use of a magnet during surgery as long as the magnet response is known and its use is feasible. [5] ICD manufacturers also recommend the use of a magnet to suspend tachyarrhythmia detection in some clinical situations. [5],[8]

   Conclusion Top

Preoperatively, patients should be informed that ICD malfunction is possible despite adequate precautions. Measures to decrease EMI should be instituted. Attention to the position of the current return pad and the surgical site with respect to the ICD is essential. Device model and programming will determine if a magnet inhibits therapy, where the magnet should be placed on the device and whether a confirmatory signal indicating inhibition of ICD function by a magnet is emitted. Magnet use and/or an improperly placed magnet may not reliably deactivate ICD sensing, and inadvertent tachyarrhythmia therapy may be delivered to the patient. Patient safety depends on our understanding of ICDs and adequate peri-operative management.

   References Top

1.Fiek M, Dorwarth U, Durchlaub I, Janko S, Von Bary C, Steinbeck G, et al. Application of radiofrequency energy in surgical and interventional procedures: Are there interactions with ICDs? Pacing Clin Electrophysiol 2004;27:293-8.  Back to cited text no. 1
2.Porres JM, Laviñeta E, Reviejo C, Brugada J. Application of a clinical magnet over implantable cardioverter defibrillators: Is it safe and useful? Pacing Clin Electrophysiol 2008;31:1641-5.  Back to cited text no. 2
3.Allen M. Pacemakers and implantable cardioverter defibrillators. Anaesthesia 2006;61:883-90.  Back to cited text no. 3
4.Joshi GP. Perioperative management of outpatients with implantable cardioverter defibrillators. Curr Opin Anaesthesiol 2009;22:701-4.  Back to cited text no. 4
5.Crossley GH, Poole JE, Rozner MA, Asirvatham SJ, Cheng A, Chung MK, et al. The Heart Rhythm Society (HRS)/American Society of Anesthesiologists (ASA). Heart Rhythm 2011;8:1114-52.  Back to cited text no. 5
6.Rozner MA. The patient with a cardiac pacemaker or implanted defibrillator and management during anaesthesia. Curr Opin Anaesthesiol 2007;20:261-8.  Back to cited text no. 6
7.Casavant D, Haffajee C, Stevens S, Pacetti P. Aborted implantable cardioverter-defibrillator shock during facial electrosurgery. Pacing Clin Electrophysiol 1998;21:1325-6.  Back to cited text no. 7
8.Practice advisory for the perioperative management of patients with cardiac implantable electronic devices: Pacemakers and implantable cardioverter- defibrillators: An updated report by the American Society of Anesthesiologists task force on perioperative management of patients with cardiac implantable electronic devices. Anesthesiology 2011;114:247-61.  Back to cited text no. 8
9.Jacob S, Panaich SS, Maheshwari R, Haddad JW, Padanilam BJ, John SK. Clinical applications of magnets on cardiac rhythm management devices. Europace 2011;13:1222-30.  Back to cited text no. 9
10.Stone ME, Apinis A. Current perioperative management of the patient with a cardiac rhythm management device. Semin Cardiothorac Vasc Anesth 2009;13:31-43.  Back to cited text no. 10
11.Effects of electrocautery on St. Jude Medical implantable cardioverter defibrillators (ICDs). Available from: [Last accessed on 2011 Dec].  Back to cited text no. 11
12.Medtronic. Magnet use for suspending Medtronic ICD detection. Available from: [Last accessed on 2011 Dec].  Back to cited text no. 12
13.Jongnarangsin K, Thaker JP, Thakur RK. Pacemakers and magnets: An arranged marriage. Heart Rhythm 2009;6:1437-8.  Back to cited text no. 13
14.Lee S, Fu K, Kohno T, Ransford B, Maisel WH. Clinically significant magnetic interference of implanted cardiac devices by portable headphones. Heart Rhythm 2009;6:1432-6.  Back to cited text no. 14

Correspondence Address:
Yiliam F Rodriguez-Blanco
Department of Anaesthesiology/Division of Cardiac Anaesthesia, University of Miami Miller School of Medicine, 1611 NW 12th Avenue. Central Building C-302, Miami FL, 33136
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0971-9784.105372

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