Impact of right or left sided radiation therapy for breast cancer in patients with atrial fibrillation on procedural findings and follow-up results of RF- catheter ablation

Backround: Current approaches in breast cancer radiation therapy (RT) seek to minimize myocardial exposure due to its known cardiotoxic effects. However, depending on the site of RT therapy, myocardial exposure varies. Data on RT associated atrial cardiomyopathy and its potential role in the pathophysiology of atrial fibrillation (AF) is very limited. 

Objectives: To investigate the effect of breast cancer radiotherapy (RT) on atrial cardiomyopathy and its possible role in the pathophysiology of atrial fibrillation. What is the therapeutic success of antral pulmonary vein isolation (PVI) with possible substrate modifications (CFAE) in patients with breast cancer radiation therapy depending on the site of radiation therapy. 

Methods: This retrospective analysis included patients who received either right-sided (rRT) or left-sided RT (lRT) for breast cancer and underwent subsequently 3D mapping guided AF ablation. Intraprocedural mapping data and short- and long-term results of ablation were evaluated according to "no low voltage" and "low voltage" present. Low voltage amplitudes in bipolar electrograms were defined as <0.5 mV for endocardial maps created during SR and <0.3mV during AF. Ablation strategy comprised pulmonary vein isolation (PVI) ± additional substrate modification according to the mapping results.  Follow Up (FU) was evaluated using repetitive 7-days Holter ECG and clinical visits. 

Results: 45 patients (all female,70.9±7.2 years) with AF (18/45 paroxysmal, 27/45 persistent) were included. 16/45 patients had received rRT, 13/45 lRT, and two patients had both rRT and lRT. Overall, in 3D mapping, 60% of the patients (27/45) showed left atrial low voltage (LV group), with no significant differences between the site of RT (rRT 56,3%, lRT 61,5%). However, the anterior wall was affected in 100% of lRT patients, whereas in rRT patients, only 55,6% showed anterior wall low voltage. In case of left atrial low voltage, 55,6% of rRT patients, but only 37,5% of lRT patients obtained sinus rhythm after the first ablation.  In lRT patients, 46,2% and in the rRT group,37,5% received a PVI and CFAE ablation. For freedom of recurrence, lRT patients required an average of 1,8 ablations and the rRT 1,6 ablations. In the group with no low voltage (18/45 patients), no significant differences between rRT and lRT patients were detected. 61.1% of the patients were recurrence-free after one ablation and freedom from recurrence was achieved in 72.2% after an average of 1.2 ablations.

Conclusion: Thoracic radiation therapy in patients with breast cancer can lead to low voltage in the LA. The site of RT has an influence on the distribution of low voltage areas. Left-sided RT leads to significantly higher rates of anterior low voltage areas than right-sided RT. Nevertheless, an extended ablation strategy (PVI & CFAE) can show good treatment options in these patients with atrial fibrillation, with high freedom from recurrence after a mean of two ablation procedures.