Consistent PR blocks include which combination of block types?

• A. 3rd Degree Block
• B. 1st Degree Block and 2nd Degree Type 2
• C. 2nd Degree Type 1
• D. 1st Degree Only

Answer: (B)

Understanding AV block patterns on telemetry hinges on how the PR interval behaves from beat to beat. Consistent PR blocks are ones where the PR interval pattern stays predictable even when a beat isn’t conducted.

First-degree AV block shows a PR interval that is uniformly prolonged on every beat, so the PR stays consistently long. Second-degree block type II (Mobitz II) features dropped QRS complexes without a changing PR interval on the beats that do conduct—the PR remains the same when a beat is transmitted. In contrast, second-degree block type I (Wenckebach) has progressively lengthening PR intervals before a dropped beat, so the PR isn’t consistently the same. Third-degree block eliminates a reliable PR relationship entirely because atria and ventricles beat independently.

Seeing both a consistently long PR interval and occasional dropped beats can occur when multiple levels of block coexist—first-degree block with Mobitz II. In such a pattern, you’d observe sections with a constant, prolonged PR and others where a beat is dropped, all without a sudden, irregular shift in the PR of the conducted beats. That mixed scenario fits the idea of consistent PR blocks, which is why the combination of first-degree block and second-degree type II is the best choice.