**1.2 Regular rhythm vs. irregular rhythm**

The next step would be to determine if the rhythm is regular or irregular. The RR interval can be used to decide if the rhythm is regular or irregular ECG. If the rhythm is regular,

**Figure 2.** *Regular RR interval. The length of blue, red and green arrows are equal showing the regularity of the RR interval.*

*ECG Approach to Narrow QRS Complex Supraventricular Tachycardia DOI: http://dx.doi.org/10.5772/intechopen.112151*

**Figure 3.**

*Irregular RR interval. The length of blue, red and green arrows are not equal showing the irregularity of the RR interval.*

**Figure 4.** *Long RP interval. The RP interval (green arrow) is more than half of RR interval (blue arrow).*

the RR intervals will be equal, but if it is irregular, the RR intervals will be anything but equal. If the RR interval is regular, it's a regular narrow QRS complex rhythm, **Figure 2**. If the RR interval is irregular, it's an irregular narrow QRS complex rhythm, **Figure 3**.

**Figure 5.** *Short RP interval. The RP interval (green arrow) is less than half of RR interval (blue arrow).*
