In the top strip, the P-P Interval is somewhat irregular with an average rate of +/- 65/min. None of the P waves are conducted and an Escape Junctional Focus surfaces at a rate of +/- 40/min, so this is Third Degree AV Block. Since the QRS Complex is narrow, the block is AV Nodal.
The nex day (5/19) on the second strip, the atrial rate is similar, but note that when the R to P is “just right”, the P wave is conducted. The shorted R-R cycle (1.40 sec) identifies the capture beats, so this is Second Degree (High Grade) AV Block.
The following day (5/20) on the third ECG strip, a slower sinus rate results in typical Second Degree Type I AV Block (Wenckebach)
Since the conduction abnormalities were not due to drugs, and the effective rate is slow, a Dual Chamber Pacemaker was warranted.
Read More about Conduction Blocks at the AV Node (AV Blocks)