Which node assumes pacemaker activity when the SA node is not functional?

Which node assumes pacemaker activity when the SA node is not functional?

• A. AV node
• B. SA node
• C. Purkinje fibers
• D. Bundle of His

Answer: (A)

If the primary pacemaker (the SA node) stops working, the heart relies on the next fastest automatic tissue to keep the rhythm. The AV node has its own automaticity and can generate impulses at about 40–60 beats per minute, providing a backup pace and maintaining conduction to the ventricles, though at a slower rate. This is why the AV node is the usual secondary pacemaker. The Purkinje fibers can take over only if both the SA node and AV node fail, producing an even slower ventricular escape rhythm around 20–40 bpm. The bundle of His is a conduction pathway, not a primary pacemaker, so it doesn’t set the rhythm under normal backup conditions.

If the primary pacemaker (the SA node) stops working, the heart relies on the next fastest automatic tissue to keep the rhythm. The AV node has its own automaticity and can generate impulses at about 40–60 beats per minute, providing a backup pace and maintaining conduction to the ventricles, though at a slower rate. This is why the AV node is the usual secondary pacemaker. The Purkinje fibers can take over only if both the SA node and AV node fail, producing an even slower ventricular escape rhythm around 20–40 bpm. The bundle of His is a conduction pathway, not a primary pacemaker, so it doesn’t set the rhythm under normal backup conditions.