Which EKG finding typically indicates a first degree AV block?

Which EKG finding typically indicates a first degree AV block?

• A. A normal PR interval
• B. A shortened PR interval
• C. A consistently prolonged PR interval
• D. Absent P waves

Answer: (C)

A consistently prolonged PR interval is a hallmark finding of first-degree AV block. In this condition, the conduction through the atrioventricular (AV) node is delayed, which results in a prolonged duration of the PR interval, typically exceeding 200 milliseconds. This indicates that while each atrial impulse reaches the ventricles, the delay in transmission is consistent but not complete, hence maintaining a regular relationship between P waves and QRS complexes.

In a first-degree AV block, the electrical impulses from the atria take longer than normal to be conducted through the AV node, but every impulse is eventually conducted to the ventricles. This condition usually manifests on an EKG as a series of P waves that are consistently spaced from their corresponding QRS complexes, with each PR interval duration being prolonged but the same from beat to beat.

Understanding first-degree AV block helps in differentiating it from other types of AV blocks where you may see more significant interruptions in conduction, such as in second-degree or third-degree AV blocks. The presence of a prolonged PR interval is therefore vital for diagnosing this specific condition.