How to Compare ECG signal?

I have a ECG signal, I have already cut it in each segment (in figure: as p1 to p2 or p2 to p3). Each segment length are different. Now I want to compare those segmented signal. Is it possible?

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It depends on what you want to do. If you are determining heart rate variability, see this PubMed search: heart rate variability review. There are 1290 articles.

Remember that for HRV studies, every valid QRS complex has to be preceeded by a normal P-wave. That means a normal (not biphasic or peaked) P-wave with a normal (< 200 ms) P-R interval.