Final answer:
The SA node fires first, then the electrical impulse moves to the AV node where it pauses briefly, then continues down the bundle of His, through the bundle branches, and finally through the Purkinje fibers where it triggers ventricular contraction.
Step-by-step explanation:
Electrical Pathway after the SA Node Fires
After the patient's natural pacemaker, the sinoatrial (SA) node, fires the next step in the electrical pathway is the activation of the atrioventricular (AV) node. The electrical impulse momentarily pauses here, which allows the atria to finish contracting and empty into the ventricles. Following this pause, the impulse travels down through the bundle of His, towards the left and right bundle branches, and finally reaches the Purkinje fibers. It's through the Purkinje fibers that the impulse spreads throughout the ventricular myocardium, causing the ventricles to contract and pump blood to the rest of the body. This coordinated sequence ensures efficient heart function and is essential for maintaining proper blood circulation.