Final answer:
An impulse that originates from a source other than the sinoatrial (SA) node is known as an ectopic impulse, and the alternate source is called an ectopic focus or ectopic pacemaker.
Step-by-step explanation:
What is the Impulse Called When Originating from an Alternate Source?
The usual heartbeat is initiated by an impulse from the sinoatrial (SA) node, the heart’s natural pacemaker. When this impulse originates from a different location, it is known as an ectopic impulse, and the site where it begins is called an ectopic focus or ectopic pacemaker. Conditions such as ischemia, exposure to certain drugs, or heightened autonomic nervous system activity can stimulate an ectopic focus. This can lead to premature heart contractions, arrhythmias (deviations from normal heart rhythm), or even fibrillation (uncoordinated heart contractions), which can be life-threatening if persistent.
In a healthy heart, the impulse swiftly travels from the SA node via internodal pathways to the atria, the atrioventricular node, and eventually to the ventricles. However, when an ectopic impulse occurs, the electrical activity of the heart deviates from this natural pattern, which can be detected using an electrocardiogram (ECG).