Cardiotoxicity of some medical anti-cancer treatment and radiotherapy (RT) is well known for breast cancer (BC) patients. However, heart rhythm disorders are almost absent of research in this area, while many studies have reported cases of syncope, atrioventricular block or atrial fibrillation occurring several years after cancer treatment.

To evaluate whether BC treatment, in particular RT, is associated with an increased risk of cardiac arrhythmias and conduction disorders (ACD) characterized by implantation of a pacemaker or defibrillator or hospitalization for rhythm disorders possibly associated with interventional procedures (EP Study and/or ablation).

Our study is based on the Echantillon Généraliste de Bénéficiaires (EGB), the 1/97 random sample of Système National des Données de Santé, the French nationwide health database. Within the EGB we will identify patients treated for BC between 2008 and 2012 after excluding cases of prevalent cancer, arrhythmia or conduction disorders and identify incident cases of ACD arising post BC and until December 2017. The ACD incidence rates in the population of BC according to the BC treatment (surgery±chemotherapy±RT) will be estimated and compared to the national incidence rates estimated from the whole EGB population by age and calendar year standardization.

With an initial cohort of approximately 260 000 women in the EGB, we plan to identify nearly 3 000 patients treated for BC between 2008 and 2012. Based on the estimation of PM or DEF implantations or AF cases in France, we should observe approximately 5 000 incident cases of ACD in the general population and 60 incident cases in the BC subgroup if the BC treatment has no effect. The observation of at least 85 cases instead of 60 (RR=1.4) will have a statistical power of 80%.

The study is ongoing. It will allow quantifying the excess risk of ACD suspected for BC treatment, in particular mediastinal RT.