## 4 Discussion
Stratifying patients by PVC occurrence revealed that lower HRV often coincides with a higher number of PVCs, supporting the hypothesis that reduced HRV is a marker of electrical instability and arrhythmic risk [18; 19; 21]. This was especially apparent during the interdialytic period, where autonomic imbalance and insufficient heightened vulnerability to arrhythmias. The analysis of the 14 blocks (B1-B14) of HRV in the three classes for female patients reveals differences in the patterns of autonomic regulation over time. Class 1 has the highest overall variability (highest SDNN) and highest sympathetic activity (highest LF). Class 2 has lower HRV values overall, suggesting lower autonomic regulation. Class 3 shows the lowest overall variability, with lower SDNN and SD2, suggesting lower autonomic adaptation capacity. Changes in the dynamic HRV vector reveal fluctuations in SDNN and RMSSD; in Class 1, these values vary significantly between blocks, suggesting a higher dynamic autonomic response, while in Class 2 and Class 3, they are more stable but with lower values, suggesting lower flexibility of the autonomic nervous system. In the frequency domain, Class 1 shows a sympathetic predominance (elevated LF) with peaks in B3 and B9, while Classes 2 and 3 have lower LF and HF values, indicating a lower autonomic activation in general. Finally, the LF/HF ratio for Class 1 has the highest ratio, indicating a sympathetic predominance. Classes 2 and 3 present a lower and more stable ratio, which may reflect a lower autonomic activity. The differences between classes are significant (\(p<0.001\)), indicating that HRV dynamics are different among groups. When analyzing the data from the male group, it is observed that Class 1 has significantly higher HRV values, while Class 2 and Class 3 show lower values. However, Class 3 has a lower RMSSD and HF, suggesting a greater decrease in parasympathetic tone. The differences between Class 2 and Class 3 are less marked in SDNN and LF, but RMSSD and SD1 are much lower in Class 3, indicating lower parasympathetic regulation. Again, there are significant differences in all indices among the three classes (\(p<0.001\)). Despite fewer PVCs, Class 3 reduced HRV may indicate a worse prognosis. Low HRV is associated with an increased risk of cardiac mortality, arrhythmias susceptibility, and adverse cardiovascular outcomes [31]. The diminished autonomic adaptability of the ANS can reduce the heart's functional capacity to respond to physiological stress, increasing cardiovascular risk in the long term [32]. This new stratification highlights how autonomic patterns influence the electrical stability and arrhythmia risk. By correlating HRV metrics to PVCs' occurrence, it becomes possible to understand the impact of autonomic imbalance contribution to electrical instability. Determining which class presents the highest risk requires further analysis. If the presence of PVCs is considered the main indicator, Class 1 would be the riskiest, as a high incidence of PVCs is closely linked to a higher risk of complex arrhythmias, electrical instability, and adverse cardiovascular events. However, it is also reasonable to argue that Class 3 could represent a higher risk due to lower HRV indices, suggesting a limited adaptive capacity of the ANS. Although this group shows the lowest number of PVCs, this does not necessarily imply a lower cardiovascular risk. On the contrary, a reduced HRV may be a marker of a compromised autonomic system that can less respond to stressful stimuli, thus increasing the likelihood of serious events. Regarding the limitations, some recordings were incomplete or affected by unlabeled artifacts. The PVC detection method depends on morphology and may misclassify beats due to high inter-patient variability. Only one ECG lead was used, limiting applicability to multichannel recordings. The algorithm's performance is sensitive to parameter tuning and may not generalize to populations with high physical activity.