Fig. (2).

Typical Wenckebach behaviour. An ECG demonstrating the 4 key elements of typical Wenckebach behaviour. The duration of the ventricular pause can be calculated by deducting the difference in the longest and the shortest PR intervals from 2x the PP interval i.e. 2(PP) - (PR4-PR1) = 2(780) - (380-260) = 1560-120 = 1440ms. The change in RR interval is determined by the difference between the 2 PR intervals forming the resulting RR interval that is being assessed, such that; R1 - R2 = PP + PR2 - PR1 = PP + 0.32 - 0.26 = PP + 0.06. Repeating this approach demonstrates that with each successive prolongation in PR interval, the relative RR intervals decrease by R2-R3 = 0.04 ms and R3-R4 = 0.02 ms respectively.