The Complexity of Pacemaker Management in Patients Undergoing Proton Beam Therapy

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EP LAB DIGEST. 2024;24(1):1,8-9.

Neil Sanghvi, MD, FACC, FHRS, and Paul Begley, BS, IBHRE Testamur, CDRMS, First Coast Heart and Vascular, Jacksonville, Florida

Pacemakers have introduced an added level of complexity for patients requiring radiation therapy. Proton beam therapy (PBT) is a cutting-edge radiation therapy used to treat a variety of malignancies. The combined magnetic environment coupled with directed radiation therapy highlight concerns for pacemaker function. We present a case illustrating the challenge of managing a pacemaker patient requiring PBT.

Case Presentation

The patient is a 77-year-old man with a history of intermittent complete heart block implanted with a left-sided thoracic Eluna 8 DR-T pacemaker with Setrox S leads (Biotronik) in 2016. The entire system is considered magnetic resonance imaging (MRI) conditional. The patient is not dependent on his device, with 50% average right ventricular pacing. He developed an aggressive right upper lung spindle cell carcinoma. He was initiated on PBT therapy unbeknownst to our clinic. The tumor location was not in the same axial, sagittal, or coronal plane as the pacemaker per the radiation center (Figure). We discovered that his device had reverted to a “backup mode” through remote monitoring. The patient underwent in-office testing, which revealed appropriate parameters and no evidence of premature battery drain. His device was reprogrammed back to his baseline parameter (DDD) and the patient was released home. He required several PBT sessions from May 2023 to July 2023, with each session resulting in backup mode (DDI) along with loss of all diagnostic and patient-specific data on the pacemaker. Beam strengths ranged from 16 cobalt gray equivalents (CGE) to 28 CGE. Each session involved 2 beams, with each beam lasting 60-75 seconds. Fortunately, the patient did not experience any adverse events as a result of the device reset. Remote follow-up was tremendously valuable in this case, since each reset was noted the day following therapy, allowing for reprogramming of the device in a timely fashion. An attempt to program the pacemaker in an asynchronous (DOO) mode was unsuccessful in preventing the device reset during PBT. Of note, there was no evidence of permanent changes in pacemaker lead sensing, thresholds, or battery longevity.

Discussion

Over 1 million pacemakers are implanted annually worldwide, including approximately 200,000 pacemakers within the United States.¹ As such, it is becoming increasingly common for patients with new diagnoses of cancer to also have a history of prior pacemaker implantation. The presence of pacemakers adds an added level of complexity since the malignancy may be eligible for PBT.

PBT is thought to impact pacemaker function due to the scatter of neutrons produced from nuclear fragment reactions within the linear accelerator. Proton therapy, photon energy of >10 MV, or electron energy of >20 MeV are all considered high risk for neutron production.² Multiple factors are thought to determine the effect of radiation therapy on cardiac implantable electronic devices (CIEDs), including device type, proximity of device to the radiation beam, radiation energy, dose rate, and available shielding.³ The highest risk factors involve neck or thoracic treatment, >5 Gy cumulative dose of radiation, and the use of PBT versus photon therapy. Photon therapy is thought to have a lower risk since the lower energy photons do not typically produce the neutron scatter that results in CIED malfunction. There is limited data evaluating the function of CIEDs during and after PBT. Twenty percent of pacemakers have been noted to reset in patients receiving PBT,⁴ though Ueyama et al described a 28.7% incidence of pacemaker malfunction.⁵ It is notable that there appears to be no significant difference in reset rates between pacemakers and defibrillators. There does not appear to be any successful approach to reprogramming the CIED to prevent device reset.

Precautions need to be taken for the CIED patient being considered for PBT. Patients who are 100% pacemaker dependent are considered at the highest risk for PBT given the frequency of device reset and potential pacing inhibition. Tumor location and subsequent beam direction play a role, since tumors from remote and from the neck and thorax may have a lower potential for device reset. Total predicted device radiation should be calculated, since absorption of >5 Gy elevates risk to device function. Devices should be programmed into MRI-conditional mode per manufacturer recommendations. A CIED technician may need to be present during therapy to address any device-related issues during or after therapy. The 2017 Heart Rhythm Society expert consensus statement recommends weekly evaluations for patients undergoing radiation therapy resulting in high risk for neutron contamination as well as for pacemaker-dependent patients.⁶ Remote device monitoring may provide the necessary frequency of monitoring as well as convenience for patients.

Summary

This case serves as a reminder of the care required for CIED patients undergoing PBT. Programming a pacemaker into an asynchronous mode does not appear to avoid device reset in the PBT magnetic environment, likely due to direct neutron contamination of the pacemaker circuitry. However, remote follow-up provides a convenient method for CIED monitoring to address any therapy-related device issues. 

Acknowledgement. Special thanks to Nelson Miksys, PhD, MCCPM, at Akerman Cancer Center in Jacksonville, Florida.

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

References

1. Greenspon AJ, Patel JD, Lau E, et al. Trends in permanent pacemaker implantation in the United States from 1993 to 2009: increasing complexity of patients and procedures. J Am Coll Cardiol. 2012;60(16):1540-1545. doi:10.1016/j.jacc.2012.07.017

2. Fradley MG, Lefebvre B, Carver J, et al. How to manage patients with cardiac implantable electronic devices undergoing radiation therapy. JACC CardioOncol. 2021;3(3):447-451. doi:10.1016/j.jaccao.2021.08.005

3. Chan MF, Young C, Gelblum D, et al. A review and analysis of managing commonly seen implanted devices for patients undergoing radiation therapy. Adv Radiat Onc. 2021;6(4):100732. doi:10.1016/j.adro.2021.100732

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5. Ueyama T, Arimura T, Ogino T, et al. Pacemaker malfunction associated with proton beam therapy: a report of two cases and review of literature—does field-to-generator distance matter? Oxf Med Case Reports. 2016;2016(8):190-194. doi:10.1093/omcr/omw049

6. Indik J, Gimbel J, Abe H, et al. 2017 HRS expert consensus statement on magnetic resonance imaging and radiation exposure in patients with cardiovascular implantable electronic devices. Heart Rhythm. 2017;14(7):e97-e153. doi:10.1016/j.hrthm.2017.04.025