If the SA node fails, what is the intrinsic rhythm of the AV node?

If the SA node fails, what is the intrinsic rhythm of the AV node?

• A. 40 to 50 beats per minute
• B. 60 to 100 beats per minute
• C. 20 to 40 beats per minute
• D. 80 to 90 beats per minute

Answer: (A)

When the primary pacemaker (the SA node) fails, the heart relies on a backup pacemaker with automaticity in the conduction pathway below it. The AV node acts as this secondary pacemaker, and its intrinsic rhythm is slower, around 40–60 beats per minute. The option showing 40–50 bpm sits squarely within that AV nodal escape range, making it the best choice. The SA node typically drives 60–100 bpm, and the Purkinje/Ventricular system can pace at about 20–40 bpm, so those ranges reflect other parts of the conduction hierarchy. The 80–90 bpm range is not characteristic of AV nodal automaticity.

When the primary pacemaker (the SA node) fails, the heart relies on a backup pacemaker with automaticity in the conduction pathway below it. The AV node acts as this secondary pacemaker, and its intrinsic rhythm is slower, around 40–60 beats per minute. The option showing 40–50 bpm sits squarely within that AV nodal escape range, making it the best choice. The SA node typically drives 60–100 bpm, and the Purkinje/Ventricular system can pace at about 20–40 bpm, so those ranges reflect other parts of the conduction hierarchy. The 80–90 bpm range is not characteristic of AV nodal automaticity.