Thoracic radiation is a known risk factor for coronary artery disease, diastolic dysfunction and conduction disturbances. Although atrial and ventricular arrhythmias were reported in case-control studies in the 1990s, to our knowledge no studies have been conducted to evaluate the arrhythmic burden after thoracic radiation in individual patients. In addition, recent studies provided evidence for acute changes in the cardiac conduction properties after and during radiation. This study aimed to evaluate the arrhythmic changes after thoracic radiation.

In a retrospective cohort study, all cardiac implantable electronic device examinations (2012-2022, n = 52047) of 10283 patients were identified. Complete radio-oncological data were available for 268 patients with implantable devices (pacemaker or implantable cardioverter defibrillator) and a medical history of radiation. In this cohort, 92 patients received thoracic radiation while 176 received radiation to other areas of the body. The total number of follow-up examinations was 1075 and the mean follow-up was 300 days. As a second control cohort, data from propensity score-matched (1:3) patients with a cardiac implantable device but no medical history of radiation was used. The matching covariates included age, sex, pre-existing coronary artery disease, cardiac valvular heart disease, heart failure with reduced ejection fraction, pre-existing atrial fibrillation, number of cardiovascular risk factors, and cardiological drug therapy. After matching, the analysis included 628 patients who did not receive radiation, and 222 patients who received radiotherapy. In an exploratory approach, the burden of atrial (time of atrial fibrillation) and ventricular (number of arrhythmic events) arrhythmia as well as the burden of atrioventricular conduction defects (percentage of ventricular pacing) were compared within the irradiated cohort and with the control cohort using Kruskal-Wallis- and Wilcoxon Rank Sum Tests. The analyses revealed that patients with a history of thoracic irradiation experienced atrial fibrillation significantly less frequently (0.055% [± 0.48] vs. 1.1% [± 6.3], p = 0.007) than patients with a history of non-thoracic radiation. The number of ventricular events per month (0.74 [± 3.8] vs. 0.94 [± 6.7], p = 0.245) and the ventricular pacing (37.1% [± 43.5] vs. 28.0% [± 37.3], p = 0.227) showed no significant differences between the groups. Compared to the second control cohort, patients with a medical history of thoracic radiation had significantly less atrial fibrillation time (0.055 [± 0.48] vs. 1.8 [± 9.9], p = 0.005) and significantly more events of ventricular arrhythmia per month (0.74 [± 3.8] vs. 0.32 [± 1.5], p = 0.016). The percentage of ventricular pacing showed no significant differences (37.1 [± 43.5] vs. 28.6 [35.6], p = 0.411).

In conclusion, thoracic radiation was associated with a significant reduction in atrial fibrillation time and a significant increase in ventricular arrhythmic events in cancer patients with implantable devices within the first year after radiotherapy.