Interpretation
There is a Junctional Focus in command at a rate of 70/min and it conducts retrogradely in alternate beats.
Another explanation is depicted later in the rhythm strip in which all of the junctional stimuli are retrogradely transmitted (note the dimple of a P wave after the QRS complex in lead V1 marked with arrow).
Probably this man has dual AV node pathways – one conducting up faster (F) and the other slowly (S)
