Background: A variety of indexes has been applied to complex fractionated atrial electrograms (CFAEs) of atrial fibrillation (AF) aimed at characterizing the atrial substrate. However, often the reported results miss the assessment of intra-recording and intra-patient stability of the analyzed data, as well as CFAEs signal quality, which may lead to biased and unreliable results. This work introduces a study in which nonlinear indexes have been applied to assess intra-recording and intra-patient stability of CFAEs. Furthermore, the presence of artifacted or noisy segments in CFAEs has been considered as well.
Methods: A total of 204 AF bipolar recordings with CFAEs of 16 seconds in length were recorded from patients with paroxysmal (n=15) and persistent (n=19) AF. They were divided into 1, 2 and 4 s-length segments to analyze intra-recording and intra-patient stability by computing the Determinism (DET) of Recurrence Quantification Analysis (RQA) and Sample Entropy (SE). Stability was evaluated with the coefficient of variation (CV = sigma\mu), with sigma the standard deviation and mu the mean of the index under study. The analyses were repeated discarding artifacted or noisy CFAE segments.
Results: Intra-recording analysis showed a significant variation of CV(%) in any segment length both for DET and SE (see table below, averaged values are shown). Discarding segments (DeltaD) benefited stability decreasing CV with deeper decreases for longer segments. Intra-patient stability also provided large variations in CV(%) for DET and even bigger for SE at any segment length. In this case discarding segments (DeltaD) was useless and CV provided limited variations. Kruskal-Wallis test revealed significant differences in DET and SE values among channels, independently from the discarding process.
Conclusion: The high variability of the CV has revealed that averaging data in one recording or among measurement sites may lead to an unfair oversimplification of CFAE-based atrial substrate characterization.