In a complete AV block, how is the ventricular QRS morphology typically described?

In a complete AV block, how is the ventricular QRS morphology typically described?

• A. Narrow QRS complex
• B. Wide QRS complex due to ventricular origin
• C. No QRS complexes
• D. Inverted QRS in all leads

Answer: (B)

In complete AV block, the atria and ventricles beat independently because the impulse from the atria cannot conduct to the ventricles. The way the ventricles depolarize depends on where the escape rhythm starts below the block. If the escape focus is in the ventricular tissue (below the AV node and His-Purkinje system), depolarization spreads through the ventricular myocardium rather than via the fast conduction system, so the QRS complexes are broad. This wide QRS typically exceeds 120 ms. If the escape rhythm were higher, such as in the AV node or near the His bundle (junctional escape), the ventricles would be activated through the normal conduction pathway and the QRS would be narrow. The common, reliable presentation in complete AV block is a wide QRS due to ventricular origin. The other patterns (no QRS or inverted QRS in all leads) don’t reflect the typical dissociated ventricular rhythm seen in this condition.

In complete AV block, the atria and ventricles beat independently because the impulse from the atria cannot conduct to the ventricles. The way the ventricles depolarize depends on where the escape rhythm starts below the block. If the escape focus is in the ventricular tissue (below the AV node and His-Purkinje system), depolarization spreads through the ventricular myocardium rather than via the fast conduction system, so the QRS complexes are broad. This wide QRS typically exceeds 120 ms.

If the escape rhythm were higher, such as in the AV node or near the His bundle (junctional escape), the ventricles would be activated through the normal conduction pathway and the QRS would be narrow. The common, reliable presentation in complete AV block is a wide QRS due to ventricular origin. The other patterns (no QRS or inverted QRS in all leads) don’t reflect the typical dissociated ventricular rhythm seen in this condition.