If You Are Not Sure the Pacemaker is Working, Do Not Forget the Magnet

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EP LAB DIGEST. 2023;23(6):21-22.

Cardiac implantable electronic devices (CIEDs) have revolutionized remote telemonitoring and patient management since the first implantation of an internal pacemaker in 1958.¹ Continuous cardiac monitoring allows for early and accurate detection of life-threatening arrhythmias. Patients with implantable devices require regular follow-up to assess health status as well as in-depth analysis of arrhythmias and device integrity.¹ The prevalence of CIEDs continually increases, with new implants exceeding 1.5 million each year worldwide.² Approximately 200,000 cardiac pacemakers are implanted annually for patients with conduction abnormalities.³

Implanted pacemakers typically undergo interrogation with either a pacing system programmer (PSP) or via a remote monitoring system. However, the utility of applying a simple magnet over the device to check functionality should not be forgotten. Pacemakers are built with magnet-sensitive reed switches, which when triggered, will set the pacemaker into an asynchronous (atrial, ventricular, or atrioventricular) pacing mode.⁴ This mode will stay triggered for as long as the magnet remains applied to the device. A magnet application can demonstrate the pacemaker’s ability to pace the heart and provide an indication on the status of the battery longevity (based on the presence of pacer spikes and its rate in pulses per minute). At the time of the original implant, pacemaker battery life for single-chamber pacemakers ranges from 7-12 years and 5-10 years for dual-chamber pacemakers.⁵ Newer models may have longer battery longevity. A pacemaker may respond to the placement of a magnet with an audible tone that may be specific to the manufacturer.⁶

This case report emphasizes the use of a simple ring magnet in evaluating pacemaker functionality in an older male patient with no cardiac follow-up 13 years post implantation.

Case Presentation

This patient is an 89-year-old man who presented for preoperative cardiac clearance for removal of squamous cell carcinoma of the scalp. He reported that during a partial colectomy in 2006, he experienced an episode of asystole; a dual-chamber Adapta Pacing System (Medtronic) was subsequently implanted. He followed up with a cardiologist until 2010. He did not have his pacemaker replaced or checked until 2023, when he presented to his cardiologist for cardiac clearance. He denied any cardiac complaints, including fatigue, shortness of breath, chest pain, presyncope, or syncope. He was not on any medications. His 12-lead electrocardiogram (ECG) showed a left bundle branch block (LBBB) pattern and atrial premature contractions (PACs). The patient was referred to our electrophysiology (EP) practice to interrogate the device.

Discussion

Figure 1A demonstrates a normal sinus rhythm with PACs and LBBB. A LBBB with a superior axis QRS is typical of right ventricular pacing, which was standard practice in the mid-2000s when the device was implanted. No pacing spike was visible prior to the LBBB either because it was not present (eg, a true conducted and nonpaced QRS complex) or due to a diminished voltage output by the device and difficult-to-recognize pacemaker spike.

The pacemaker was easily palpable in the left prepectoral area without evidence of erosion. Attempts at interrogation with a Medtronic tablet-based programmer and PSP failed to identify the device. A programmer can fail to interrogate a device if it is from a different manufacturer, not compatible with the device (eg, a newer device using outdated software), or the device is no longer functional (eg, dead battery). Figure 1A shows the 12-lead ECG with no discernable pacemaker spikes or change in rhythm. The suspicion was that this was the patient’s native rhythm and not paced. To prove the point, a ring magnet was applied directly over the patient’s pacemaker pulse generator (left pectoral region) while an ECG was recorded (Figures 1B and 2). The magnet would result in asynchronous pacing at 65 beats per minute with a LBBB pattern (which would also occur when the battery voltage reached its elective replacement indicator).⁵ This simple magnet method confirmed that the pacemaker was unresponsive and had a dead battery.

A call was placed to the referring cardiologist and a recommendation was made to electively replace the pacemaker. The risks, benefits, and alternatives were discussed. The patient elected not to replace the device.

It is important to note that patients with dual-chamber pacemakers are also at risk of developing pacemaker- mediated tachycardia (PMT). This reentrant man-made arrhythmia can develop when a retrograde atrial electrogram is sensed outside the post ventricular atrial refractory period (PVARP) and ventricularly paced following a preprogrammed atrioventricular delay.⁷ The device can be programmed to prevent or break the PMT by extending the PVARP. However, when a programmer is not available, a simple magnet application over the device may be used to break the PMT. The magnet can trigger asynchronous pacing and terminate the tachyarrhythmia by removing the antegrade limb of the reentrant circuit.⁷

In addition, pacemaker magnets have an important use in the perioperative setting. Some surgical procedures carry a high risk of exposing a patient’s pacemaker to electromagnetic interference. This could potentially cause oversensing and asystole in a patient who is pacemaker dependent. To mitigate this risk, pacemakers can be reprogrammed preoperatively to asynchronous mode. Alternatively, a magnet may be placed and taped over the device to accomplish the same task for the duration of a surgical procedure.⁶ 

Conclusion

Pacemaker functionality can be confusing, especially in the presence of a LBBB. In this patient, the possibility of underlying sinus rhythm with a LBBB pattern mimicking the rhythm of a functioning pacemaker was considered. This case emphasizes that if there is uncertainty as to whether a pacemaker is working, a simple ring magnet application over the device while recording an ECG can help make that determination. A ring magnet can be obtained from one of the pacemaker manufacturers and should be available at any cardiology or EP clinic. In other words, if the pacemaker is not working, do not forget the magnet. 

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. They report no conflicts of interest regarding the content herein.

References

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