A 76 year-old gentleman presents for a pacemaker check 4 months post implant. High ventricular rate episodes are noted, as shown below. He is asymptomatic during episodes:

 

 

 

 

 

 

The device is programmed DDD-R 60 – 100. Presenting rhythm and device parameters are shown below.
What is the diagnosis?

 

 

 

 

 

 

 

 

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