Which of the following AV blocks can be described as a gradually lengthening PR interval until ultimately the final P wave in the group fails to conduct?

Question

a. First-degree AV block c. Second-degree AV block, type II
b. Second-degree AV block, type I d. Third-degree AV block

Answer 1

B
In Mobitz type I block, the atrioventricular (AV) conduction times progressively lengthen until a P wave is not conducted. This typically occurs in a pattern of grouped beats and is observed on the electrocardiogram (ECG) by a gradually lengthening PR interval until ultimately the final P wave in the group fails to conduct. When all atrial impulses are conducted to the ventricles but the PR interval is greater than 0.20 second, a condition known as first-degree AV block exists. Mobitz type II block is always anatomically located below the AV node in the bundle of His in the bundle branches or even in the Purkinje fibers. This results in an all-or-nothing situation with respect to AV conduction. Sinus P waves are or are not conducted. When conduction does occur, all PR intervals are the same. Because of the anatomic location of the block, on the surface, ECG the PR interval is constant and the QRS complexes are wide. Third-degree, or complete, AV block is a condition in which no atrial impulses can conduct from the atria to the ventricles. This is also described by the term complete heart block.