In second-degree AV block type I, the PR interval _____.
A) shortens
B) is absent
C) is inconstant
D) remains constant

Question

Quizplus · Accepted Answer

In second-degree AV block type I, the PR interval is inconstant and the PR interval after a nonconducted P wave is shorter than the interval preceding the nonconducted beat. Although progressive lengthening is a phrase that was used for many years to describe the behavior of the PR intervals associated with second-degree AV block type I, use of this terminology is no longer recommended; rather, the term inconstant or generally progressive PR intervals is recommended. Use of the term inconstant or generally progressive PR intervals is important because many type I AV blocks are atypical, missing one or more of the features of the classic Wenckebach phenomenon. For example, the second conducted PR interval after a blocked impulse may fail to show the greatest increase in length; instead, the PR interval may actually shorten and then lengthen in the middle of a grouped beating pattern. Alternately, the duration of the PR intervals may show no obvious change in the middle or for a few beats just before the end of a group.

In Second-Degree AV Block Type I, the PR Interval _____