RCIS Practice Test 2025 – All-in-One Exam Prep

The correct response indicates that the SA node is not involved in the delay of the PR interval when it measures .26 seconds. The PR interval primarily reflects the time it takes for electrical impulses to travel from the atria through the AV node and into the ventricles.

The SA node is responsible for initiating the electrical impulse that leads to atrial contraction. While it sets the rhythm of the heartbeat, it does not contribute to the conduction delay that occurs at the AV node or in the pathways that follow.

In cases where the PR interval is prolonged, it typically indicates a delay within the conduction pathways that follow the SA node, particularly at the AV node, where conduction can slow down before the impulse reaches the Bundle of His and the Purkinje fibers. These subsequent structures are directly involved in the process that reflects the measure of the PR interval. Hence, the remaining choices include components of the conduction pathway that either experience delays or propagate the impulse to the ventricles.