How is the PR interval affected in a Wenckebach AV block?

How is the PR interval affected in a Wenckebach AV block?

• A. It lengthens progressively until a P wave is blocked
• B. It remains constant throughout the cycle
• C. It shortens progressively until a QRS is dropped
• D. It fluctuates with each heartbeat

Answer: (A)

In a Wenckebach AV block, the defining characteristic is the progressive lengthening of the PR interval with each heartbeat, culminating in the eventual dropping of a QRS complex. This phenomenon is known as "Mobitz Type I" or "Wenckebach." The mechanism involves a gradual delay in conduction through the AV node, leading to a longer PR interval until the electrical impulse fails to get through, resulting in a blocked P wave. This pattern of progressive lengthening is a hallmark feature that distinguishes Wenckebach from other types of AV blocks, making it critical for identifying this specific arrhythmia on an EKG. Recognizing this pattern allows healthcare providers to understand the underlying electrical dynamics of the heart in this type of heart block.