What does the following ECG indicates?

OSSSC Nursing Officer-2021

Medical & Surgical Nursing

Hard

Appeared in: OSSSC Nursing Officer-2021

Explanation

The ECG shows a regular rhythm where every P wave is followed by a QRS complex, indicating a 1:1 atrioventricular conduction.
The defining characteristic visible in the image is a fixed and prolonged PR interval, which is consistently greater than the normal upper limit of 0.20 seconds (5 small squares).
This constant delay in electrical conduction from the atria to the ventricles without any missed beats is the hallmark of a first-degree heart block.
The absence of dropped QRS complexes rules out second-degree and third-degree heart blocks.

Option A: Complete heart block (also known as third-degree heart block) involves a complete dissociation between atrial (P waves) and ventricular (QRS complexes) activity. The ECG would show P waves and QRS complexes occurring at their own regular rates but independent of each other. This is not seen in the given ECG.
Option C: Second-degree heart block is characterized by the intermittent failure of AV conduction, meaning some P waves are not followed by a QRS complex ('dropped beats'). The provided ECG shows a QRS complex following every single P wave.
Option D: Third-degree heart block is synonymous with complete heart block. It features complete AV dissociation, where the atria and ventricles beat independently. The ECG strip clearly shows a consistent relationship between P waves and QRS complexes.

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) heart blocks as background academic context rather than a clinical decision trigger.
While often benign, nurses must monitor patients with first-degree AV block for any signs of progression to higher-degree blocks, such as dizziness, syncope, or worsening fatigue.
A key nursing intervention is to review the patient's medication record for drugs that can prolong AV conduction (e.g., beta-blockers, calcium channel blockers, digoxin, amiodarone) and report findings to the healthcare team.
What if? If the ECG showed the same prolonged PR interval but with occasional P waves not followed by a QRS complex, the diagnosis would change to Second-Degree AV Block, Type II. This is a more serious condition that often requires pacemaker implantation due to the risk of progressing to complete heart block.

How to Approach the Question

This is an image-based question requiring ECG interpretation. Follow a systematic approach.
Step 1: Assess the rhythm by checking the R-R intervals. In this ECG, they are regular.
Step 2: Identify the P waves and their relationship to the QRS complexes. Observe if there is one P wave for every QRS complex. Here, the ratio is 1:1.
Step 3: Measure the PR interval (from the start of the P wave to the start of the QRS). Determine if it is within the normal range (0.12-0.20s). In this case, it is visibly longer than 5 small squares, hence prolonged.
Step 4: Check if the prolonged PR interval is constant or if it changes. Here, it is constant.
Step 5: Synthesize the findings. A regular rhythm with a 1:1 P:QRS ratio and a fixed, prolonged PR interval is the definition of a first-degree heart block.

Concept Tested & Keywords

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E6 Medicine Harrison 22e Part 1 p. 1966-1968

E6 Physiology Ganong 27e Vol 2 Part 1 p. 77-79