In patients with cardiovascular implantable electronic devices, asynchronous pacing is necessary for surgeries with a risk of electromagnetic interference. Magnets are often used for asynchronous pacing. In this case report, magnet application to a Biotronik Evia DR-T pacemaker (Biotronik) programmed to a magnet response mode called automatic magnet mode (AUTO) led to a brief period of asynchronous pacing before reverting to prior settings, an unexpected response that was not revealed on the preoperative interrogation report. For Biotronik pacemakers programmed to the AUTO mode, changes in programming are needed for asynchronous pacing.
Perioperative management of pacing-dependent patients may require asynchronous pacing to prevent oversensing of electromagnetic interference (EMI) by the pacemaker.1–4 Magnet application is one way this is accomplished. Pacemaker manufacturers have sophisticated technologies with varied responses to a magnet, which can have important implications intraoperatively. We describe a case of magnet application to a Biotronik Evia DR-T pacemaker (Biotronik) programmed to a magnet response mode called AUTO. All Biotronik pacemakers have 3 modes of magnet response: automatic magnet mode (AUTO), synchronous magnet mode (SYNC), and asynchronous magnet mode (ASYNC). The AUTO mode is the manufacturer’s default magnet response mode.5–9 Anesthesiologists should be aware of the characteristics of the Biotronik pacemaker magnet modes, have strategies to identify each magnet response, and, when needed, contact a cardiovascular implantable electronic device (CIED) expert to adjust pacemaker settings for surgery. The patient provided Health Insurance Portability and Accountability Act of 1996 written authorization for the publication of this case report.
An 88-year-old woman with poorly controlled hypertension, stage 4 chronic kidney disease, type 2 diabetes mellitus, coronary artery disease, heart failure with preserved ejection fraction, carotid stenosis, paroxysmal atrial tachycardia, and a dual-chamber Biotronik Evia DR-T pacemaker (Biotronik) implanted for symptomatic bradycardia presented for left hemithyroidectomy for a 2.2-cm thyroid nodule. The preoperative interrogation report performed by an electrophysiologist showed that her pacemaker was programmed to synchronous dual-chamber pacing (DDD) at 60 to 120 beats per minute (bpm). The interrogation report also indicated that the patient’s intrinsic rhythm was sinus bradycardia with a heart rate of 40 bpm. Right atrial-pacing occurred 92% of the time and right ventricular-pacing occurred 1% of the time. The pacemaker had a battery life of >3 years. The electrophysiologist reported that a magnet will cause asynchronous pacing at 90 bpm and suggested magnet use if monopolar electrosurgery is used. The use of electromyography with the Medtronic Nerve Integrity Monitoring Response 3.0 System (Medtronic Xomed) was planned to prevent recurrent laryngeal nerve injury as well as electrosurgery. Since this patient was pacing-dependent, the intraoperative plan was to apply a magnet to convert the pacemaker to an asynchronous mode at 90 bpm.
We utilized continuous electrocardiography and peripheral pulse monitoring via the pulse oximetry plethysmogram to monitor the functionality of the patient’s pacemaker. A magnet was applied over the pulse generator a few minutes before induction. Asynchronous dual-chamber pacing (DOO) pacing occurred at 90 bpm. After 10 beats, the pacemaker reverted to a DDD pacing mode at a rate of 60 bpm. The magnet was repositioned 3 times with a similar pacing response and then an abrupt return to the DDD pacing mode. We delayed the case by 45 minutes and consulted the electrophysiology service to program the device to DOO.
The patient was induced with lidocaine, fentanyl, propofol, and succinylcholine. Temporary transcutaneous pacing and defibrillation equipment were immediately available. She was intubated with a 7.0 endotracheal tube and started on a remifentanil infusion. After intubation, the electrophysiologist interrogated the pacemaker and confirmed that the programmed magnet mode was AUTO. The Biotronik pacemaker was reprogrammed from DDD 60–120 bpm to DOO 90 bpm. The patient subsequently had an uncomplicated and uneventful thyroidectomy and was extubated at the end of the case. She was taken to the postanesthesia care unit, where her pacemaker was programmed to its preoperative settings before discharge.
The use of electrosurgery within 15 cm of the pulse generator of the pacemaker is a known risk factor for EMI.1–3,9 Standard risk mitigation strategies include positioning the dispersive electrode to divert the electrical return pathway away from the pulse generator and leads, using short bursts of monopolar electrosurgery or using bipolar electrosurgery.1,2,10 The nerve monitoring often used for thyroid surgery is a form of electromyography where a monopolar probe stimulates the recurrent laryngeal nerve to produce vocal cord motion, which is detected by surface electrodes on a specialized endotracheal tube.11 The risk of EMI with pacemakers and nerve monitoring systems during neck surgery is theoretical, as there are no reported incidents. However, the use of asynchronous pacing for pacing-dependent patients in surgeries where electromyography will be used near the pacemaker is recommended.1–4
Magnets are commonly used to change a pacemaker to an asynchronous pacing mode. For some pacemakers, the magnet response can be programmed by a CIED expert. Lack of awareness of magnet response can lead to incorrect conclusions of pacemaker malfunction.1,3,6,7,12 Biotronik has 3 modes of magnet response: AUTO, SYNC, and ASYNC.5–9 The magnet response with the AUTO mode directs a pacemaker to asynchronously pace (ie, DOO) at a rate of 90 bpm for 10 beats, after which the pacemaker reverts to the original pacing mode.3,5,8 The AUTO mode can be used to obtain 10-beat electrocardiograms with pacing to assess device function with certain features disabled, such as the event counter, and may be more comfortable for patients while these assessments are made according to Biotronik.5,6 A Biotronik pacemaker in the SYNC mode will not respond to magnet application with asynchronous pacing, but will continue with the original pacing settings. The SYNC mode is often used for patients having dizziness or palpitations to remotely capture electrocardiograms by applying a magnet during these episodes, which can later be reviewed by a cardiologist.5,9 A device in the ASYNC mode will asynchronously pace at 90 bpm until the magnet is removed. The magnet response of Biotronik pacemakers also changes when the pulse generator is due to be replaced.5,7,9 In the ASYNC mode, the asynchronous pacing rate with magnet application decreases to 80 bpm. In the SYNC and AUTO modes, the pacing rate decreases by 4.5% to 11% with magnet application.5
Our patient presented with a Biotronik pacemaker programmed to the AUTO mode, which is the factory default magnet response mode for all Biotronik pacemakers.5–7 In 1 report, 6 of 38 Biotronik pacemakers that were interrogated at a single center were in the AUTO mode.8 It is important for anesthesiologists to identify patients presenting for surgery with Biotronik pacemakers with AUTO as the magnet response mode who require asynchronous pacing. The interrogation report may state that the magnet response is AUTO and include headings labeled “magnet cycle 1–10” with an asynchronous pacing mode, such as DOO, and “magnet cycle 11…” with the original pacing mode.7 If the Biotronik pacemaker magnet response is not available in the interrogation report, providers can contact Biotronik (800-547-0394) or apply a magnet preoperatively to confirm the magnet response.
To achieve sustained asynchronous pacing, a Biotronik pacemaker programmed to the AUTO mode must either be reprogrammed to asynchronous pacing without changing the magnet response mode or the magnet response mode must be changed to the ASYNC mode, and a magnet applied for the duration of the case.5,7 The advantage of changing the magnet response mode to the ASYNC mode is the ease of switching between asynchronous pacing and the patient’s regular pacing mode, which ultimately minimizes the time spent in asynchronous pacing. However, there are several challenges that may preclude magnet use, including prone or lateral positioning, obese patients, or patients with deep tissue CIED implantation where a magnet may not exert its intended effect.3,4 Furthermore, some CIED experts may be less familiar with Biotronik pacemakers or find changing the magnet mode to be more technically challenging, and prefer reprogramming to asynchronous pacing.8 Before patients leave the postanesthesia care unit, it is important to restore reprogrammed Biotronik pacemakers to the original pacing settings and ensure that the pacemaker has not entered an emergency backup mode.1–4 If the pacemaker magnet mode is changed from the AUTO mode to the ASYNC mode, consider discussing with a CIED expert whether to leave the patient’s pacemaker in the ASYNC mode, so a magnet can be used for sustained asynchronous pacing in the future.
There is documentation of varied magnet responses in the operative setting of pacemakers developed by Biotronik and other manufacturers.2,7,8,13,14 Boston Scientific and Abbott pacemakers can also be programmed with or without the feature of asynchronous pacing with magnet application.13,14 Additionally, it is important to note that in patients who are dependent on pacing from an implantable cardioverter-defibrillator (ICD), magnet application will only disable antitachycardia therapy in most cases, and some ICDs are programmed to have no response to magnets.1–3 Pacing-dependent patients with an ICD will need preoperative device reprogramming to asynchronous pacing if EMI is anticipated.
For perioperative pacemaker management, identification of the manufacturer, the pacing mode, proper functionality, and magnet response is necessary.1–4 If a surgical procedure requires asynchronous pacing, confirming the pacemaker magnet response via the interrogation report, consulting an expert, or calling the manufacturer is best practices, but not always possible. This case illustrates that applying a magnet to a pacemaker to confirm the expected magnet response before proceeding with surgery is an essential step in perioperative planning for pacing-dependent patients. Furthermore, though it can be difficult to stay abreast of the widespread field of CIEDs and programmable features developed by manufacturers, prompt recognition of unfamiliar responses of the device when a magnet is applied, as occurred in this case, is important for anesthesiologists.