A nurse is reviewing a client’s cardiac rhythm strips and notes a constant P-R interval of
0.35 seconds. Which of the following dysrhythmias is the client displaying?
A.
Premature atrial complexes
B.
Complete heart block
C.
Atrial fibrillation
D.
First-degree atrioventricular block
The correct answer and Explanation is :
The correct answer is D. First-degree atrioventricular block.
Explanation:
A first-degree atrioventricular (AV) block is characterized by a prolonged PR interval, which is the time it takes for the electrical impulse to travel from the atria to the ventricles through the AV node. In a normal heart rhythm, the PR interval ranges from 0.12 to 0.20 seconds. When the PR interval exceeds this range, as in this case where it is consistently 0.35 seconds, it indicates a delay in the conduction through the AV node, which is characteristic of a first-degree AV block.
First-Degree AV Block:
- PR Interval: The defining feature is a consistently prolonged PR interval, greater than 0.20 seconds. In this case, the PR interval is 0.35 seconds, which fits the criteria for first-degree AV block.
- Conduction: All atrial impulses are conducted to the ventricles, but with a delay. The QRS complex is typically normal and appears after the prolonged PR interval.
Here’s why the other options are not correct:
A. Premature Atrial Complexes:
- These are early beats originating in the atria and are characterized by a premature P wave. They do not affect the PR interval consistently; rather, the PR interval may be normal or slightly altered during these early beats.
B. Complete Heart Block:
- Also known as third-degree AV block, this condition involves a complete disconnection between the atria and ventricles. The PR interval is not consistent; instead, there is a complete dissociation between atrial and ventricular rhythms. This is not the case here, where the PR interval is constant.
C. Atrial Fibrillation:
- In atrial fibrillation, there is an irregularly irregular rhythm with no distinct P waves and an irregular ventricular response. The PR interval is not measurable in atrial fibrillation due to the lack of consistent P waves.
In summary, a constant PR interval of 0.35 seconds aligns with the diagnosis of a first-degree atrioventricular block, reflecting a prolonged delay in AV node conduction.