In tracing "a" of Figure 1, there seems to be only one P wave in front of each QRS complex, suggesting sinus rhythm. However, during the compensatory pauses after the PVCs (↑) in tracing "b," there ...

Wide QRS regular tachycardia is present in Figure 1. No definite P waves are identifiable. There is one PVC in the lower tracing. During the compensatory pause, there is definitely a P wave (↓ on ...