The irregularity factor
Mechanistic insights into beat-to-beat irregularities in atrial fibrillation cycle length
Natasja M.S. de Groot (TU Delft - Electrical Engineering, Mathematics and Computer Science, Erasmus MC, TU Delft - Mechanical Engineering)
Lianne N. van Staveren (Erasmus MC)
Eva A.H. Lanters (Erasmus MC)
Vehpi Yildirim (Erasmus MC)
Richard Hendriks (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Rudolf A. de Boer (Erasmus MC)
Hemanth Rammanah (Haga Ziekenhuis)
Mathijs S. van Schie (Erasmus MC)
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Abstract
BACKGROUND: Measures derived from the atrial fibrillation (AF) cycle length (AFCL) are used to identify regions crucial for AF maintenance or predict (ablation) treatment outcomes. However, mechanisms underlying beat-to-beat irregularities in AFCL are unknown. OBJECTIVE: We aimed to (1) investigate beat-to-beat changes in AFCL (Δ-AFCL) by relating temporal variation in AFCL with quantified beat-to-beat changes in activation patterns and conduction times (Δ-CTs) and (2) test whether the irregularity factor (IF) (standard deviation of the Δ-AFCL histogram) is indicative of the complexity of activation patterns. METHODS: Mapping was performed in 24 patients with long-standing persistent AF (LSPAF) and a reference group (n = 25, patients with induced [acute] AF). At the mapping area center, Δ-AFCL was calculated by subtracting each AFCL from the preceding AFCL and related to causes of Δ-CT (CT(N) - CT(N-1)) of fibrillation waves from the electrode array border toward the mapping area center. RESULTS: The IF was larger during LSPAF (52 ± 17 vs 25 ± 10; P < .001) than during acute AF. Δ-CTs were also larger (25 ± 8 ms vs 19 ± 7 ms; P = .005) and caused by beat-to-beat changes in conduction velocity (36 ± 6 cm/s vs 29 ± 6 cm/s; P = .001) and beat-to-beat changes in direction (94° ± 13° vs 64° ± 22°; P < .001); beat-to-beat changes in path length (13 ± 4 mm vs 14 ± 3 mm; P = .333) were comparable. The IF correlated with conduction block [probability (ρ) = 0.887], lines of conduction block lengths (ρ = 0.900), number of fibrillation waves (ρ = 0.889), and prevalence of focal waves (ρ = 0.609) (P < .001 for all). CONCLUSION: The IF indicates the underlying complexity of activation patterns, is higher during LSPAF than during acute AF, and is comparable throughout the atria during LSPAF. It is a novel, easy-to-calculate, objective electrical biomarker, which can be used for, for example, guiding patient-tailored treatment independently of the AF mechanisms.
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