Final answer:
A PAC, or a premature atrial contraction, is an early heart contraction that originates from the atrium. These premature beats from the atrium can be detected on an electrocardiogram (ECG) and are generally harmless.
Step-by-step explanation:
The correct answer is D) premature beat from the atrium. A PAC, or a premature atrial contraction, is an early heart contraction that originates from the atria. It occurs when an electrical signal is generated by a different part of the atria than the normal sinus node, causing an early and, occasionally, irregular heartbeat. These premature beats from the atrium can be detected on an electrocardiogram (ECG) and are generally harmless, but if they occur frequently or are associated with symptoms, they may require further evaluation and treatment.