Question

In an ECG displaying Second-Degree AV Block - Type II, what characteristic feature distinguishes it from other heart block types?

A) Progressive prolongation of PR interval
B) Randomly dropped QRS complexes
C) Consistently prolonged QT interval
D) Absence of P waves

Answer 1

On an ECG, a Second-Degree AV Block - Type II is characterized by randomly dropped QRS complexes without a preceding change in PR interval length, distinguishing it from other types of heart blocks.

Step-by-step explanation:

The characteristic feature that distinguishes a Second-Degree AV Block - Type II from other heart block types on an ECG is B) Randomly dropped QRS complexes. In this condition, some impulses from the SA node do not lead to subsequent QRS complexes. This is different from a Second-Degree AV Block - Type I, where there is a progressive prolongation of the PR interval before a QRS complex is dropped, leading to a pattern where the PR intervals get longer and then a QRS complex is dropped.

Unlike Third-Degree AV Block where there is no correlation between the P waves and QRS complexes, in Second-Degree AV Block - Type II, the atrial rhythm (as seen in the P waves) is usually regular, but there is a periodic non-conduction of a P wave without a preceding prolongation in the PR interval (unlike in Type I, also known as Mobitz I or Wenckebach phenomenon).