Temporal relationship between high-intensity training sessions and episodes of atrial fibrillation among previously inactive patients with paroxysmal or persistent AF

Abstract Background Exercise is considered beneficial for managing comorbidities in atrial fibrillation (AF) patients in the long term, and emerging evidence also indicate that high-intensity interval training (HIIT) may reduce AF burden and symptoms. However, more data on the impact of individual training sessions on recurrence of AF is needed to understand mechanisms and tailor exercise recommendations. Purpose To assess the temporal relationship between training sessions and recurrent AF episodes among previously inactive patients with paroxysmal or persistent AF being introduced to HIIT. Methods The Norwegian Exercise in Atrial Fibrillation Trial is a multi centre randomized controlled trial including inactive patients with paroxysmal or persistent AF, who are randomly assigned to either a structured exercise intervention or control for 12 months. We analysed AF episodes and training data from the initial weeks with introduction to structured exercise in the intervention group (8 supervised sessions of HIIT at 85-95% of maximal heart rate). AF episodes lasting ≥30 seconds were registered using implantable cardiac monitors (ICM). Training sessions were registered using sports watches and manual logs. We report event rates and rate ratios for recurrent AF episodes during HIIT compared to episodes occurring outside HIIT. Due to non-normal data distribution statistical comparisons were performed using the Wilcoxon sign-ranked test. Results 81 patients (24 female, 57 male), mean age of 64.2 years (range 35-78), were included. 57 patients had paroxysmal and 24 had persistent AF. The combined duration of monitoring was 5272 days (median 53, range 30 – 163). The participants performed a total of 418 hours of HIIT (median 5.3 hours, range 0.67 – 6.58) during 615 training sessions (median 8, range 1 – 8). In total 4528 AF episodes (median 4, range 0 – 1693) were registered, of which 18 occurred during HIIT. The mean AF rate per 24 hours was 0.69 outside HIIT, 1.20 during HIIT, 0.92 for the periods 1 – 3 hours and 4-6 hours after HIIT (Figure 1). The rate ratio for AF during HIIT compared to outside HIIT was 1.73 (p=0.002). In the 52 participants with at least one episode of AF during follow-up, the rate ratio for AF during HIIT compared to outside HIIT was 10.4 (bootstrapped 95% CI 0.2 to 30.3). Conclusion Among previously inactive patients with paroxysmal or persistent AF, the rate of recurrent AF episodes was significantly higher during high-intensity exercise than outside exercise. Given the few AF episodes, this mechanism of trigging AF by high-intensity exercise needs further investigation.Mean AF per 24 hours