The 12 Rhythms of Christmas: High-Grade AV-Block

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. In our recent articles we’ve discussed three different types of AV-block that cause dropped P-waves: type I, type II, and 2:1 AV-block. Consider the prototypical tracings from each article: Figure 1. Type I AV-block. Figure 2. Type II AV-block. Figure 3. 2:1 AV-block of uncertain mechanism. Each shows different conduction ratios—ranging from 2:1 to 3:2 to 4:3—but they don’t demonstrate something like 3:1 conduction, where two P-waves in a row would be blocked before the third one conducts. That’s because we classify that with another distinct term: High-Grade AV-Block 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. Figure 4. High-grade AV-block with 3:1 conduction. There are 3 P’s for every 1 QRS. 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 ...
Source: EMS 12-Lead - Category: Cardiology Authors: Tags: 12 Rhythms of Christmas Vince DiGiulio Source Type: research