How does 2nd-degree AV block type 1 differ from type 2 on the PR interval pattern?

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Multiple Choice

How does 2nd-degree AV block type 1 differ from type 2 on the PR interval pattern?

In second-degree AV block, the pattern that distinguishes type I from type II is how the PR interval behaves before a dropped beat. In type I, the PR interval progressively lengthens from one beat to the next until a P wave is not followed by a QRS complex—the dropped beat marks the end of the cycle, and the PR interval then starts over. This creates a repeating pattern of longer and longer PRs with occasional missed QRS. In contrast, type II shows a constant PR interval from beat to beat, with occasional dropped QRS complexes that occur without preceding PR prolongation. The P waves remain present, and the key feature is the lack of PR lengthening before the nonconducted beat. So the description that best captures the difference is the progressive lengthening of the PR interval with a dropped beat. The idea of a dropped beat with a constant PR reflects type II, and normal or absent P waves isn’t the defining contrast between these blocks.

In second-degree AV block, the pattern that distinguishes type I from type II is how the PR interval behaves before a dropped beat. In type I, the PR interval progressively lengthens from one beat to the next until a P wave is not followed by a QRS complex—the dropped beat marks the end of the cycle, and the PR interval then starts over. This creates a repeating pattern of longer and longer PRs with occasional missed QRS.

In contrast, type II shows a constant PR interval from beat to beat, with occasional dropped QRS complexes that occur without preceding PR prolongation. The P waves remain present, and the key feature is the lack of PR lengthening before the nonconducted beat.

So the description that best captures the difference is the progressive lengthening of the PR interval with a dropped beat. The idea of a dropped beat with a constant PR reflects type II, and normal or absent P waves isn’t the defining contrast between these blocks.

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