Emergency Medical Technician (EMT) Intermediate Practice Exam

Which of the following is NOT a component of the cardiac electrical conduction system?

1. SA node

2. AV node

3. Interatrial septum

4. Purkinje fibers

The correct answer is: Interatrial septum

The cardiac electrical conduction system consists of specialized structures that generate and propagate electrical impulses throughout the heart, coordinating its rhythmic contractions. The sinoatrial (SA) node is the primary pacemaker of the heart, located in the right atrium, responsible for initiating the heartbeat. The atrioventricular (AV) node, situated at the junction between the atria and ventricles, serves as a gatekeeper, slowing down the electrical signal before it enters the ventricles to ensure proper timing of contractions. The Purkinje fibers are specialized conductive fibers that spread the electrical impulse rapidly throughout the ventricles, triggering their contraction. The interatrial septum, however, is a muscular wall that divides the left and right atria. While it is an essential anatomic structure of the heart, it does not play a direct role in the electrical conduction pathway like the SA node, AV node, and Purkinje fibers do. Therefore, it is appropriate to identify the interatrial septum as the option that does not belong to the cardiac electrical conduction system.