A potential source of bias is that the decision to switch to
the alternative therapy was dependent upon physician and patient
opinion and perception rather than an objective, measurable criteria.
It is possible that patients undergoing catheter ablation were biased
toward believing that the treatment was effective in comparison to
patients treated with antiarrhythmic medications. Likewise, physicians
may have been more likely to recommend catheter ablation than substitute medication when drug therapy failed. These biases may explain at
least in part the crossover imbalance but they do not mitigate the objective evidence demonstrating that RFA preserved its efficacy better than
AAD therapy during long-term follow-up. That is, at two years AF
burden was significantly lower and more patients were free from AF
in the pure RFA than in the pure AAD. In contrast, the potential bias in
crossover strengthen ourfindings as only the patients with the best
response to AAD therapy should have been included in the pure AAD
group whereas some patients with no objective evidence of treatment
success may have been included in the RFA group.