This rhythm is 2° AV block Type I, Wenckebach. While it is easily recognizable (I hope!), the actual criteria, or electrocardiographic findings, are worth reviewing.
1. progressive lengthening of the PR interval until a P wave is blocked
2. progressive shortening of the RR interval until a P wave is blocked
3. the RR interval containing the blocked P wave is shorter than the sum of 2 PP intervals
When Type I 2° AV block does not precisely follow these relationships it is typically due to underlying sinus arrhythmia, which alters the RR interval, which in turn will affect the RP and PR intervals of subsequent beats.
Because of the periodic pauses, the rhythm shows “group beating,” a finding that frequently leads to consideration of the diagnosis of Wenckebach phenomenon.