What would a junctional focus third degree AV block look like on an EKG?

What would a junctional focus third degree AV block look like on an EKG?

• A. Normal P waves with accelerated QRS complexes
• B. Some independent P waves and normal QRS complexes
• C. Regular P waves and wide QRS complexes
• D. Inefficient atrial activity with no QRS complexes

Answer: (B)

In a third-degree AV block, also known as complete heart block, there is a dissociation between the atrial and ventricular activity. This means that the atria and the ventricles beat independently of each other. A junctional focus may take over the ventricular pacing, which alters the characteristics observed on the EKG.

The correct interpretation sees some independent P waves, which result from atrial contraction, and normal QRS complexes that are generated by the junctional pacing mechanism. The atrial rate remains consistent with the P waves while the ventricular rate may vary or be slower, depending on the rate of the junctional focus. This independence is what makes option B correct, as it accurately describes the presence of P waves without a rigid relationship to the QRS complexes. The junctional focus helps maintain ventricular activity, hence the QRS complexes appear normal rather than wide, which would indicate a different rhythm such as a bundle branch block.

This subtlety in the relationship between atrial and ventricular pacing is crucial in diagnosing AV blocks, especially when observing the EKG readings.