The ECG shows group beats in which the last beat is a PVC and the others are sinus beats (shown as “S”).
The first step in the ECG interpretation is determining the rhythm. so first look for p waves. the best leads for recognizing the p waves are lead II and V1. if you can’t see P waves in these leads, look at all the leads. in this strip P waves are visible in the lead V3. Note that some of P waves are hidden behind the prior T waves.