Which rhythm shows progressively lengthening PR interval before a dropped beat?

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Multiple Choice

Which rhythm shows progressively lengthening PR interval before a dropped beat?

Progressive PR prolongation with a dropped beat is the Wenckebach pattern of AV block, also known as Mobitz type I. In this rhythm, conduction through the AV node gradually worsens so the PR interval lengthens with each beat until a P wave is not followed by a QRS complex. After that dropped beat, the cycle restarts with a shorter PR interval. On the ECG you’d see P waves at a regular rate, the PR interval getting longer from one beat to the next, and then a nonconducted P wave (no QRS after that P). The rhythm then repeats. This differs from a constant prolonged PR interval with every P followed by a QRS (first-degree block), from a normal rhythm with no PR changes (normal sinus rhythm), and from complete AV dissociation where P waves and QRS occur independently (third-degree block) and you don’t see this stepwise slowing leading to a dropped beat.

Progressive PR prolongation with a dropped beat is the Wenckebach pattern of AV block, also known as Mobitz type I. In this rhythm, conduction through the AV node gradually worsens so the PR interval lengthens with each beat until a P wave is not followed by a QRS complex. After that dropped beat, the cycle restarts with a shorter PR interval.

On the ECG you’d see P waves at a regular rate, the PR interval getting longer from one beat to the next, and then a nonconducted P wave (no QRS after that P). The rhythm then repeats.

This differs from a constant prolonged PR interval with every P followed by a QRS (first-degree block), from a normal rhythm with no PR changes (normal sinus rhythm), and from complete AV dissociation where P waves and QRS occur independently (third-degree block) and you don’t see this stepwise slowing leading to a dropped beat.

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