Diagram: Type I vs. Type II 2nd Degree AV Block-KH

Frank G. Yanowitz, M.D., copyright 1997

In type I 2nd degree AV block the PR progressively lenthens until a nonconducted P wave occurs. The PR gets longer by smaller and smaller increments; this results in gradual shortening of the RR intervals. The RR interval of the pause is usually less than the two preceding RR intervals. The RR interval after the pause is longer than the RR interval just before the pause. In type II AV block, the PR is constant until the nonconducted P wave occurs. The RR interval of the pause is usually 2x the basic RR interval.