What is the outcome of the PR wave in second-degree AV block (2*AVB)?

In second-degree AV block, specifically Mobitz type I (Wenckebach), the key characteristic is that the PR interval progressively lengthens with each successive beat until a QRS complex is dropped. This phenomenon occurs due to gradual conduction delays in the atrioventricular node. After the dropped QRS, the cycle repeats, starting again with a shorter PR interval.

The progressive elongation of the PR interval followed by the loss of a QRS complex is characteristic of this type of block. Understanding this pattern is crucial for identifying second-degree AV block on an ECG, as it helps differentiate it from other types of blocks and arrhythmias. The outcome of a dropped QRS after the incrementally longer PR intervals defines the classic presentation of Mobitz type I.