American Association of Critical-Care Nurses (AACN) Certification Practice Test

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What is a characteristic of Mobitz Type I (Wenckebach) heart block?

Progressive lengthening of the PR interval
Consistent PR interval
Non-conducted P waves
Fixed ventricular response

The correct answer is: Progressive lengthening of the PR interval

In Mobitz Type I heart block, also known as Wenckebach phenomenon, a defining characteristic is the progressive lengthening of the PR interval with each successive heartbeat until a QRS complex is dropped. This pattern creates a characteristic grouping where the PR interval gradually increases until a P wave is not followed by a QRS complex. This differs from other types of heart blocks, where the PR interval remains consistent or where P waves are consistently conducted or blocked without any identifiable pattern of prolongation. Therefore, the progressive lengthening of the PR interval is crucial in identifying Mobitz Type I heart block and indicates a specific type of electrical conduction issue within the heart's conduction system.