## 3 Results  
As a result of the application of the CFAE quality assessment, 5.2% of the one-second-length segments were discarded, while for the two- and four-second-length segments, the percentages were slightly higher, respectively, 8.6% and 12.5%, due to the aforesaid increased loss of discarded segments. Figure 3 shows the discarded segments distribution along the recording places in the datasets. In particular, the number of discards in the LSPV is quite low as compared with the other recording places and in contrast with the RSPV, in which the discards are more frequent. The proportion of the discarded segments in the paroxysmal and persistent AF patients is similar: for 1 s length segments, 46.4% of the discarded segments were in ParAF and 53.6% in PerAF; for the 2 s length segments, 44.4% were in ParAF and 55.6% in PerAF; and finally, for the 4 s length segments, 43.8% were in ParAF and 56.2% in PerAF. Regarding the results of the stability, the averaged statistical descriptors (range, mean, and standard deviation) resulted by applying SE to the 1, 2, and 4 s length datasets, with and without discards, reported in Table 1. With the discards, the ranges were reduced as the lower boundary took greater values mainly due to the removal of the drifts, which generally presented high amplitude and low SE values. As a consequence, the standard deviations also diminished with the discards. Figure 3: From left to right, discarding segments percentages distribution among recording places in 1 s length dataset, 2 s length dataset, and 4 s length dataset. The statistical descriptors of the DET were computed in the same way as the SE, and the results are reported in Table 2. For the DET, the ranges were reduced with discards due to the upper boundary that took lower values, thus also decreasing the standard deviations. In fact, the DET and SE are complementary measures; one measures predictability, and the other, complexity. The intra-recording analysis showed a significant variation in the CV(%) in any segment length, both for the SE and DET, as shown in Table 3. Discarding the segments benefited the stability, decreasing the CV, with deeper decreases for longer segments. These variations were on average of greater magnitude for PerAF (DET = 29.1%, SE = 37.6%) versus ParAF (DET = 19.6%, SE = 31.8%). The intra-patient stability also provided large variations in the CV(%) for the DET and even bigger for the SE at any segment length, as shown in Table 4. In this case, discarding segments was useless and the CV provided similar variations. The results of the Kruskal-Wallis test, as well as the visual inspection of the box plots computed for every recording place, every window length, and every index (72 plots not included here), suggests that the atrial electrophysiological substrate mostly differs at the recording places analyzed, and shows a great variability in the intra-patient indexing. For the 1 s length datasets, H\({}_{0}\) was always rejected for the SE, while for the DET, it was accepted only once with no discard. For the 2 s length, H\({}_{0}\) was still always rejected for the SE, while \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Length**} & \multicolumn{2}{c}{**No Discard**} & **Discard** \\ \cline{2-4}  & **Range** & **Mean \(\pm\) std** & **Range** & **Mean \(\pm\) Std** \\ \hline
**h** & [0.004–0.362] & 0.137 \(\pm\) 0.033 & [0.013–0.362] & 0.138 \(\pm\) 0.032 \\
**2 s** & [0.007–0.312] & 0.134 \(\pm\) 0.025 & [0.018–0.312] & 0.135 \(\pm\) 0.023 \\
**4 s** & [0.008–0.300] & 0.132 \(\pm\) 0.017 & [0.020–0.300] & 0.134 \(\pm\) 0.014 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Sample entropy statistical descriptors analysis results for 1, 2, and 4 s length datasets, with and without discards. The values reported were obtained by averaging among CFAE.