Changes in arrhythmogenic properties and five‐year prognosis after carbon‐ion radiotherapy in patients with mediastinum cancer

Introduction Carbon‐ion irradiation of rabbit hearts has improved left ventricular conduction abnormalities through upregulation of gap junctions. However, to date, there has been no investigation on the effect of carbon‐ion irradiation on electrophysiological properties in human. We investigated this effect in patients with mediastinum extra‐cardiac cancer treated with carbon‐ion radiotherapy that included irradiating the heart. Methods and Results In April–December 2009, eight patients were prospectively enrolled (including two male, aged 72.5 ± 13.0 years). They were treated with 44–72 Gray equivalent (GyE), with their hearts exposed to 1.3–19.1 GyE. High‐resolution ambulatory electrocardiography was performed before and after radiotherapy to investigate arrhythmic events, late potentials (LPs), and heart rate variability. Five patients had pre‐existing premature ventricular contraction (PVC)/atrial contraction (PAC) or paroxysmal atrial fibrillation (PAF)/AF; after irradiation, this improved in four patients with PVC/PAF/AF and did not deteriorate in one patient with PAC. Ventricular LP findings did not deteriorate and improved in one patient. In eight cases with available atrial LP findings, there was no deterioration, and two patients showed improvements. The low frequency/high frequency ratio of heart rate variability improved or did not deteriorate in the six patients who received radiation exposure to the bilateral stellate ganglions. During the five‐year follow‐up for the prognosis, six of the eight patients died because of cancer; there was no history of hospitalization for cardiac events. Conclusion Although this preliminary study has several limitations, carbon‐ion beam irradiation to the heart is not immediately cardiotoxic and demonstrates consistent signals of arrhythmia reduction.