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 ...
A narrow QRS tachycardia at a rate of 105 beats/min. is present. No P waves are identified in front of the QRS complexes, suggesting accelerated AV junctional rhythm. However, there are two PVCs.