What does the above Holter demonstrate?
Why is the PR interval prolonged for some of the sinus beats?
The Answer: 
What does this Holter demonstrate?
  1. Interpolated PVCs – these are ventricular ectopics that occur between two sinus beats without a pause.

  2. A phenomenon called concealed conduction where the PVCs penetrate retrogradely to the AV node – it is concealed because the only evidence that this has occurred is ‘indirect’ – ie. PR interval prolongation in the subsequent sinus beats (*).