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?

Progressively lengthening PR intervals with eventual a dropped beat define Mobitz type I AV block, also known as Wenckebach. In this pattern, conduction through the AV node slows a little with each beat, so the PR interval lengthens from one beat to the next until one atrial impulse fails to conduct to the ventricles, producing a missing QRS complex. After the dropped beat, the PR interval resets and the cycle repeats. This differs from first-degree block, where the PR interval is uniformly prolonged but remains constant with every beat and no dropped QRS occurs. It also differs from third-degree block, where there is complete AV dissociation and no reliable relationship between P waves and QRS complexes. Sinus bradycardia features a slow rate but a normal PR interval and preserved P–QRS relationship, with no progressive PR prolongation or dropped beats.

Progressively lengthening PR intervals with eventual a dropped beat define Mobitz type I AV block, also known as Wenckebach. In this pattern, conduction through the AV node slows a little with each beat, so the PR interval lengthens from one beat to the next until one atrial impulse fails to conduct to the ventricles, producing a missing QRS complex. After the dropped beat, the PR interval resets and the cycle repeats.

This differs from first-degree block, where the PR interval is uniformly prolonged but remains constant with every beat and no dropped QRS occurs. It also differs from third-degree block, where there is complete AV dissociation and no reliable relationship between P waves and QRS complexes. Sinus bradycardia features a slow rate but a normal PR interval and preserved P–QRS relationship, with no progressive PR prolongation or dropped beats.

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