Temporal Variability of Atrial Fibrillation in Pacemaker Recipients for Bradycardia: Implications for Crossover Designed Trials, Study Sample Size, and Identification of Responder Patients by Means of Arrhythmia Burden

Background: Most clinical trials that have tested pacing therapies to prevent and treat atrial tachyarrhythmias (AT) have chosen endpoints such as AT frequency or burden (defined as percentage of time a patient is in AT), but failed to show unequivocal evidence of a clinical impact. Aim: The aim of our multicenter prospective observational study was to measure the variability of AT burden and estimate its impact on study outcomes. Methods and Results: Two hundred and fifty patients indicated for permanent pacing and suffering from AT (age 71 ± 9 years; 47.2% male) received a dual-chamber pacemaker. AT burden was measured in two consecutive, 2-month observation periods; the Monte Carlo method was then applied to simulate findings of a crossover design study. We simulated several models of therapy impact, each model being characterized by the percentage of responder patients and the percentage reduction in AT burden. To show a significant impact of AT therapies in a sample of 250 patients in whom 100, 75, or 50% would be theoretical responders to therapies, AT burden reduction should be at least 27, 32, or 57%, respectively. Temporal fluctuations in AT burden were so high that about 60% of patients would falsely appear as responders or nonresponders in a crossover study, regardless of AT burden reduction. Conclusions: In patients paced for bradycardia and suffering from AT, high intrapatient variability in AT burden was measured. Various models of therapy impact showed that, in crossover trials of AT therapies, time-related fluctuations in AT burden negatively impact on sample sizes and impair the ability to identify patients as responders or nonresponders.