Figure 1 shows straightforward type I (second-degree) AV block. The QRS complexes do not occur regularly, which immediately rules out third-degree AV block, because in third-degree AV block the escape ...
Some consider 2:1 AV block to be type II block, claiming that the PR interval doesn't lengthen. What they don't realize is that determining whether the PR interval lengthens requires at least 2 ...