AV Rhythms Flashcard 2
Rationale
B. Rationale: Second-degree AV block Mobitz type 2 is a disease involving the His-Purkinje system. A block occurs after the AV node within the bundle of His, which is an all-or-none conduction system. There are no changes within the PR interval after the non conducted P wave. Studies have shown that Mobitz type 2 has a higher risk of complete heart block than Mobitz type 1.
Question
Which of the following statements differentiates second-degree AV block Mobitz type 2 from second-degree AV-block Mobitz type 1?
a. Second-degree AV block Mobitz type 2 is caused by an intermittent conduction block within the AV node
b. Second-degree AV block Mobitz type 2 is a disease involving the His-Purkinje system
c. Second-degree AV block Mobitz type 2 causes progressive prolongation of the PR interval
d. Second-degree AV block Mobitz type 2 has a lower risk of complete heart block
Answer
b. Second-degree AV block Mobitz type 2 is a disease involving the His-Purkinje system
Rationale
A. Rationale: Atrioventricular blocks are caused by a delay of impulse conduction from the atria to the ventricles, which prolongs the PR interval. The normal PR interval is 0.12–0.2 seconds. A prolonged PR interval is > 0.2 seconds.
Question
Which one of the following criteria makes for the diagnosis of AV block?
a. PR interval of 0.24 seconds
b. Peaked T waves
c. Presence of U waves
d. Wide QRS complex of 0.15 seconds
Answer
a. PR interval of 0.24 seconds
Rationale
A. Rationale: The P wave is missing in supraventricular tachycardia because the impulse generation is not located in the SA node but may be located in the atria or junctional nodes.
Question
Which one of the following is missing in supraventricular tachycardia?
a. P wave
b. QRS complex
c. T wave
d. R wave
Answer
a. P wave
Rationale
B. Rationale: The junctional pacemaker is responsible for junctional rhythms. It is a group of pacemaker cells located between the AV node and the Bundle of His. Since this focus is distal to the SA node, junctional rhythms present with a characteristic inverted P wave in the monitoring lead.
Question
Which part of the heart’s conduction system is the focus of abnormal impulse generation in junctional rhythms?
a. After the Bundle of His
b. Between the AV node and the Bundle of His
c. Before the AV node
d. After the Purkinje fibers
Answer
b. Between the AV node and the Bundle of His