Thoracic radiation is a known risk factor for coronary artery disease, diastolic dysfunction and conduction disturbances. Although atrial and ventricular arrhythmias have been reported in case control studies in the 1990s, to our knowledge no studies have been conducted to evaluate the arrhythmic load before and after thoracic radiation in individual patients.

In a retrospective cohort study, all cardiac implantable electronic device checks (2012-2022, n = 52047) from 10283 patients were included. 128 patients with implantable devices (pacemaker or implantable cardioverter defibrillator) were identified with regular checks before and after cancer radiotherapy. The total number of follow-up examinations was 813. 45 patients received thoracic radiation while 83 received radiation to other areas of the body. Baseline characteristics included age, sex, device type, mean cardiac radiation dose, cardiovascular risk factors, current medication, left ventricular ejection fraction and pre-existing medical conditions. In an unbiased approach the change in ventricular arrhythmic events before and after radiation was evaluated by optimizing a multivariate logistic regression model with the use of the Akaike Information Criterion for the covariates thoracic radiation, age, pre-existing coronary artery disease, heart failure with reduced ejection fraction, pre-existing atrial fibrillation, number of cardiovascular risk factors, and cardiological drug therapy. Based on this, the multivariate logistic regression model included cardiovascular risk factors, the use of antiarrhythmic drugs, the use of ACE-inhibitors, and thoracic radiation. Significant positive associations were found between ventricular events following thoracic radiation and the number of cardiovascular risk factors (OR = 1.6, 95% CI [1.1,2.4], p = 0.0111) and baseline use of antiarrhythmic drugs (OR = 14.8, 95% CI [1.3,190], p = 0.0261). In contrast, thoracic radiation was negatively associated with ventricular events after radiation therapy (OR = 0.15, 95% CI [0.01, 0.66], p = 0.0298).

In conclusion, thoracic radiation was associated with a significant reduction in ventricular events in cancer patients with implantable devices. Furthermore, cardiovascular risk and pre-existing rhythmic instability as denoted by the intake of antiarrhythmic drugs were associated with a significant increase in ventricular events following radiation.