Ectopic foci can be described as impulses that originate from where compared to the SA node?

• A. Secondary pacemaker sites with lower intrinsic rate
• B. From the SA node
• C. From the AV node
• D. From the Purkinje system

Answer: (A)

Ectopic foci are impulses that start from a site other than the SA node. The key point is that these secondary pacemaker sites have a slower intrinsic rate than the SA node. The SA node normally sets the pace at about 60–100 beats per minute, while nearby pacemaker areas (like the AV node or Purkinje tissue) have intrinsic rates that are lower. Therefore, when impulses originate from these non–SA-node areas, they produce rhythms that are slower and can take over only if the SA node is suppressed or conduction to it is blocked. This is why the correct description is secondary pacemaker sites with a lower intrinsic rate.