In this study, we documented the real-world clinical courses of CIED recipients undergoing RTx, such as gamma knife and photon RTx, and we noticed that clinicians still lack recognition and preparation regarding RTx-related CIED malfunction. Although the number of subjects was small during the study period, we found that 82.6% of patients with a CIED did not receive proper cardiology consultation for RTx from 2009 to 2019. This study documented that the pre- and post-RTx CIED parameters were not significantly different in patients with or without an appropriate cardiology consultation. However, it is not clear whether the post-RTx parameters in the NC group guaranteed the safety of the CIEDs even if the patients did not report a CIED malfunction after RTx. Although the device parameters of most NC group patients were in the normal range, they could not reflect the circumstances at the time RTx ended because these patients did not receive appropriate device interrogation.
Patients undergoing CIED implantation could have several comorbidities.[15] Accordingly, magnetic resonance imaging (MRI) or RTx could be indicated in a CIED recipient and can affect a CIED.[7, 16–19] The effects of MRI on CIEDs have been documented, and recommendations, including guidelines and prevention protocols, have been reported and used in the clinical field.[2, 20–23] We previously reported that, given appropriate precautions and consultations, MRI, even 3 Tesla MRI, can be performed safely in patients with a CIED.[24] Based on our experience, we developed an automatic consultation system that improved the pre-MRI consultation rate and the safety and quality of care in patients with a CIED.[25] CIED malfunctions related to RTx are easier to miss than those occurring secondary to MRI. One of our patients complained of dizziness after RTx for left breast cancer. She had a DDD-type PM on the right side and received RTx at 43 Gy (S3A Fig). At that time, the ECG revealed non-sustained ventricular fibrillation (S3B Fig). She was assigned to the PC group in this study. This case demonstrated that CIED dysfunction is difficult to identify and rarely reported. Moreover, RTx-related CIED malfunctions occur stochastically and are difficult to predict.[26, 27]
Reports indicate that CIEDs can be affected by direct ionizing radiation and photoneutrons leading to device malfunction.[26, 28] Grant et al. investigated RTx factors that caused CIED malfunctions and recommended non-neutron-producing RTx rather than neutron-producing RTx.[28] However, the mechanism and effects of radiation exposure are not clear. Several studies have demonstrated that safe radiation doses in the presence of a PM or ICD are 2–10 Gy and < 1 Gy, respectively. These levels are under the curative doses for breast and lung cancer (up to 50–60 Gy).[8–10, 29, 30] In addition to recommendations for appropriate radiation dosage, cooperation between cardiology and radiation therapy departments is necessary for the prevention and proper monitoring of RTx-related complications; however, this multidisciplinary approach seems to be rare in actual practice. Zaremba et al. reported a 3.1% CIED malfunction rate in 453 RTx courses, and 22.6–27.9% of participants underwent device interrogation before and after RTx.[6] Only 21.7% of our study participants underwent appropriate pre- and post-CIED interrogation. Although almost all CIED recipients have a risk of RTx-related device dysfunction, there is no adequate preventive management. Further, clinicians are insufficiently aware of the fact that RTx poses a risk in patients with a CIED. The 2017 Heart Rhythm Society (HRS) consensus statement recommends device relocation if there is a possibility that it could interfere with RTx. Additionally, weekly CIED evaluations are recommended for patients undergoing neutron-producing treatment.[31] Thus, the 2017 HRS consensus statement reinforces the importance of cooperation between radiation and cardiology departments when a patient with a CIED requires RTx (Fig. 2).
In our study, two malfunctions occurred in the NC group. One patient received pelvic RTx (cumulative dose, 60 Gy) for prostate cancer. He complained of orthopnea caused by lung metastasis. When the patient visited the cardiology department for a post-RTx device evaluation, we found that the lead impedance had changed from 435 to 171 ohms (S1 Fig). The other patient received left breast RTx (cumulative dose, 45 Gy). She complained of severe diarrhea after chemotherapy and died after receiving supportive care without any curative cancer treatment. A normal paced rhythm was identified on the patient’s ECG 3 months after RTx (S2 Fig). However, when the patient arrived dead at the emergency department 4 months after RTx, her ECG showed no paced rhythm (S2 Fig). Although neither ECG detected any abnormal event related to the device at that time, we could not rule out device dysfunction definitively. In another case, a 64-year-old woman scheduled to receive left breast RTx was referred to the cardiology department for PM implantation due to AV block. The cardiologist decided that the PM should be inserted in the right chest to avoid interfering with her RTx according to the guidelines (S3 Fig).
Study limitations
Our study has some limitations. First, although we enrolled all patients with PMs or ICDs who underwent RTx, our cohort was small. Thus, it was difficult to compare values between patients. We attempted to overcome this limitation by analyzing the changes in all data and comparing the differences between groups based on consultation status. However, some data, particularly post-RTx interrogation values, were missing, making it difficult to compare the two groups directly. Second, due to the retrospective nature of the study, we could only assess the device function by interrogation, which indirectly reflects potential device dysfunction. Therefore, it was difficult to accurately determine the device condition at the time of death in patients who died. Despite these limitations, our retrospective single-center review included diverse RTx target cases reflecting real-world practice. Furthermore, we believe our study provides important clinical information about the potential for CIED complications associated with RTx.