As a beginner, the main take-home message from this chapter is the concept of an “escape rhythm.” As we have seen a few times before, the intrinsic pacemaker of the heart is located in the right atrium and triggers a sinus rhythm based off its own underlying baseline rate. The sinus node is the first pacemaker because it is the fastest and takes control before the others. When it fires, it resets the other pacemakers, causing them to restart their own intrinsic clocks, which is in phase 4 of their action potential cycle. Each set of subsequent “escape” pacemakers takes longer to fire than the one before it. This is a fail-safe mechanism for the heart to maintain a functional cardiac rhythm at all times. Therefore, if one pacemaker fails, the next one will assume the responsibility and become the “escape pacemaker.”
Let’s look at the most common example: If the sinus fails, then an atrial pacemaker takes over. If those two fail, then the main atrioventricular (AV) nodal pacemakers take over, then the His bundle pacemakers, then the pacemakers in the bundles and fascicles, then the ventricular myocyte pacemakers. So, the concept of an escape pacemaker is critical to our survival. Using an analogy, if something happens to the president, then the vice president takes over. If he cannot take over, then the Speaker of House takes over, and so forth. This system ensures that someone is always in charge of the government.
So, is an escape complex a pathologic process or a survival mechanism? The answer is, it is a survival mechanism that points to pathology further up the line. The pathology lies in the defective areas of the pacemaking systems that are failing to fire, not in the escape pacer itself. This is a very important point to keep in mind clinically because you never want to abolish an escape rhythm. If you remove the ability to have that escape complex or rhythm, you are left with asystole. That is not a good thing.
—Daniel J. Garcia