What is used as a reference point to identify the changing electrical amplitude?

The isoelectric line serves as a reference point to identify changes in electrical amplitude on an electrocardiogram (EKG). This line represents a state of electrical neutrality, where there is no electrical activity detected by the electrodes. It provides a baseline against which the various phases of the cardiac cycle can be measured. When the heart's electrical activity occurs, such as depolarization and repolarization of the heart muscles, it will appear as deflections above or below this isoelectric line.

Identifying these changes is crucial for interpreting an EKG, as it allows healthcare professionals to observe abnormalities in heart rhythm and function, such as arrhythmias or ischemia. The isoelectric line being stable creates a clear reference point, enabling accurate assessment of the electrical activity during each heartbeat.