What is the conduction velocity of the SA node?

What is the conduction velocity of the SA node?

• A. 0.4 m/s
• B. 1 m/s
• C. 2 m/s
• D. 0.2 m/s

Answer: (B)

Conduction velocity through the SA node is about 1 meter per second. The SA node is made of pacemaker cells that are less tightly coupled than surrounding atrial muscle, so impulse spread inside the node is relatively slow. This slower spread helps coordinate the timing of atrial activation and keeps the heart rhythm organized. Once the impulse leaves the SA node, it enters atrial tissue where conduction is faster, and later passes through the AV node where conduction slows further to create the normal delay between atrial and ventricular activation. Among common teaching values, around 1 m/s best fits the typical description of nodal conduction. The other speeds correspond to other tissues—AV node is much slower, while atrial muscle and Purkinje fibers conduct faster.

Conduction velocity through the SA node is about 1 meter per second. The SA node is made of pacemaker cells that are less tightly coupled than surrounding atrial muscle, so impulse spread inside the node is relatively slow. This slower spread helps coordinate the timing of atrial activation and keeps the heart rhythm organized. Once the impulse leaves the SA node, it enters atrial tissue where conduction is faster, and later passes through the AV node where conduction slows further to create the normal delay between atrial and ventricular activation. Among common teaching values, around 1 m/s best fits the typical description of nodal conduction. The other speeds correspond to other tissues—AV node is much slower, while atrial muscle and Purkinje fibers conduct faster.