ECG characterized by PR interval which becomes longer with each succeeding QRS complex until there is a P wave not followed by a QRS is seen in?

1. A

   First degree AV Block

2. B

   Second Degree AV Block, Type I

3. C

   Second-Degree AV Block, Type II

4. D

   Complete Heart Block

Appeared in: NHM MP Staff Nurse - 2015

Explanation

• The question describes the hallmark feature of Second-Degree AV Block, Type I (Wenckebach): a progressive prolongation of the PR interval.
• This lengthening continues with each beat until a P wave appears without a corresponding QRS complex, which is known as a 'dropped beat'.
• The mechanism involves a functional block within the AV node, where it becomes increasingly 'fatigued' with each impulse until it fails to conduct one.
• After the dropped beat, the AV node recovers, and the cycle of progressive PR lengthening begins again.

Why Other Options Were Wrong

• Option A: In First-Degree AV Block, the PR interval is prolonged (greater than 0.20 seconds) but remains constant from beat to beat. There are no dropped QRS complexes.
• Option C: In Second-Degree AV Block, Type II (Mobitz II), the PR interval is constant before a beat is suddenly dropped. There is no progressive lengthening of the PR interval.
• Option D: In Complete Heart Block (Third-Degree AV Block), there is a complete dissociation between atrial (P waves) and ventricular (QRS complexes) activity. The PR interval is completely variable, and there is no consistent relationship between them.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain ECG Interpretation of Atrioventricular (AV) Blocks as background academic context rather than a clinical decision trigger.
• A nurse's ability to differentiate between Mobitz I and Mobitz II is critical. Mobitz I is often stable, but Mobitz II is unstable and can rapidly progress to complete heart block, a medical emergency.
• Nurses must monitor patients with any AV block for signs of decreased cardiac output, such as hypotension, dizziness, syncope, or chest pain, and be prepared to intervene.
• What if the patient is symptomatic with hypotension and altered mental status? The priority nursing action is to call for help (e.g., rapid response team), administer atropine as prescribed if the patient is unstable, and prepare for transcutaneous pacing.

How to Approach the Question

• First, identify the key components of the ECG described in the question: P waves, PR interval, and QRS complexes.
• Focus on the behavior of the PR interval. The question states it 'becomes longer with each succeeding QRS complex'.
• Note the relationship between P waves and QRS complexes. The question specifies that eventually, 'there is a P wave not followed by a QRS'.
• Synthesize these two findings: progressive PR lengthening followed by a dropped beat.
• Evaluate the options based on this pattern. Recall the definitions of each type of AV block to find the one that matches this specific description.

Concept Tested & Keywords

• Concept Tested: ECG Interpretation of Atrioventricular (AV) Blocks
• Stem keywords: ECG, PR interval, QRS complex, P wave
• Lead-in keywords: seen in

Question ID

Q6Ix_MF-M4XS-Aifi5erkv

Copy ID

Reference Book

E6 Medicine Harrison 22e Part 1 pp. 1966-1968, 1967-1969

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 647-649