This article is the eighth in our latest series, The 12 Rhythms of Christmas, where each day we examine a new rhythm disorder. It’s a continuation of the theme behind last year’s 12 Leads of Christmas.
High-grade AV-block (sometimes called advanced AV-block) is how we describe a form of pathological AV-block where two or more consecutive P-waves fail to conduct to the ventricles.
Why don’t we just call the tracing in Fig. 4 type II AV-block? Think back to the basis of our article on 2:1 AV-block: Since we never see two P-waves in a row that conduct, we cannot assess whether the PR-interval is progressively increasing (as in type I AV-block) or fixed (as in type II AV-block). You might think that all high-grade AV-blocks must be due to a type II mechanism because the conduction defect looks so severe, but even type I AV-blocks can exhibit the sort of behavior we see above. In fact, based on subsequent tracings (not shown here), there’s a pretty decent chance both the patients whose rhythms we’re going to examine in this post were experiencing high-grade AV-block due to an underlying type I mechanism.
For the rest of this discussion please follow this link or click on the rhythm strip above.