## 3 Results and Discussion
Figure 17a shows a spectrogram of a normal sinus rhythm ECG recording, where the LF and VLF ranges are brighter than the HF range, indicating higher LF power than HF power for this subject. This was consistent across all 18 normal sinus rhythm spectrograms. In contrast, Figure 17b illustrates an arrhythmia ECG recording, where the HF range is brighter, indicating higher HF power than LF power. This pattern was observed in almost all 42 arrhythmia spectrograms. However, some arrhythmia recordings (e.g., 112, 123, and 222) also showed bright areas in the LF range, as shown in Figure 18.  
Figure 18 shows accurate RR interval plots, with higher variations in the RR intervals due to the recordings themselves, not missing R peaks. These variations lead to high-magnitude events in the LF and HF regions, as seen in the spectrograms in Figure 19, suggesting an unexpected LF/HF ratio. At the power estimation stage (Table 4), the LF/HF ratio for these recordings was higher than one, deviating from other arrhythmia recordings. Missing R peaks, leading to incorrect higher RR intervals, can also be seen as high-magnitude events in spectrograms. For example, Figure 21 shows a high magnitude between 15 and 20 min in the HF range due to a missing R peak, causing the overall spectrogram to appear dimmer. This condition is observed in all six recordings with missing R peaks. The CWT spectrograms of some recordings, such as Figure 22a, show high magnitudes throughout, while others, like Figure 22b, display reduced brightness. This variation is due to each person having a unique ECG pattern, influenced by the structure of their heart, causing differences in signal magnitude and intensity [37]. The next step involved extracting frequency bands (VLF, LF, and HF) using inverse CWT, with frequency ranges set as VLF (0.003-0.04 Hz), LF (0.04-0.15 Hz), and HF (0.15-0.4 Hz) for long-term ECG recordings [36]. The power of these bands was calculated by taking the square of the RMS values of the reconstructed signals, and power values were normalized to compare their contribution to total power. The LF/HF ratio was computed to assess the sympatho-vagal balance of the ANS. The power estimates are summarized in Tables 4 and 5. While the LF and HF bands are the main focus for the LF/HF ratio, the VLF band also contributes significantly to total power. The LF band is believed to reflect both sympathetic  
Figure 10:0 CWT spectrograms of recording no. 121. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multirow{2}{*}{**Index**} & \multicolumn{3}{c}{**Power (ms\({}^{2}\))**} & \multicolumn{3}{c}{**Normalized Power (n.u)**} & \multirow{2}{*}{**LF/HF Ratio**} \\ \cline{2-2} \cline{5-8}  & **VLF** & **LF** & & & **HF** & **VLF** & **LF** & **HF** \\ \hline
233 & 122.723 & 1905.31 & 1998.67 & 23,119.26 & 0.053 & 0.082 & 0.864 & 0.095 \\ \hline
234 & 393.933 & 113.916 & 167.856 & 675.706 & 0.582 & 0.168 & 0.248 & 0.678 \\ \hline \end{tabular}
\end{table} 
Table 5: _Cont._  
Figure 22: CWT spectrograms of recordings no. (**a**) 122 and (**b**) 205.  
and parasympathetic activity, while the HF band reflects parasympathetic activity [38; 39; 40], though some studies suggest the LF band represents sympathetic activity [41; 42]. However, the LF/HF ratio is considered an indicator of the sympatho-vagal balance of ANS activity [43; 44; 45]. The power estimates for the Normal Sinus Rhythm dataset in Table 4 show that normalized HF power is lower than LF power in most recordings, suggesting better activity in the LF range, potentially leading to an LF/HF ratio greater than one. Recording no. 16,539 shows an LF/HF ratio of 0.42, the lowest observed in Table 4. Unlike the other recordings, this one has a higher normalized power for the HF band than the LF band, resulting in a lower LF/HF ratio. The RR interval plot of this recording exhibited significant variation in the RR intervals, likely due to the variations in the ECG recording itself.