How does Wenkebach (Mobitz type 1) second degree heart block manifest on an ECG?

Wenckebach, also known as Mobitz type 1 second-degree heart block, is characterized by a progressive lengthening of the PR interval until a QRS complex is dropped. This manifests on the ECG as a pattern where you will initially see a consistent PR interval, which gradually increases (or lengthens) with each successive beat. Eventually, this prolongation reaches a point where there is a failure to conduct the electrical impulse through the AV node, resulting in the dropping of a QRS complex. The sequence then resets, and the cycle repeats.

This distinctive progressive nature of the PR interval is a hallmark feature of Wenckebach heart block, differentiating it from other types of heart block where the PR interval may remain constant or have a different pattern. Therefore, when interpreting an ECG that exhibits these characteristics, one would expect to see the specific progression of PR intervals leading up to a dropped QRS complex.