What does a premature atrial contraction demonstrate?

• A. An early contraction of the atrium
• B. A delayed contraction of the ventricle
• C. An extended ventricular rhythm
• D. A normal sinus rhythm

Answer: (A)

A premature atrial contraction (PAC) is characterized by an early depolarization of the atrium, which leads to an early heartbeat that occurs before the regular sinus beat would. This event results from an ectopic focus in the atrium that initiates an impulse prematurely. The early contraction interrupts the normal rhythm and can cause the heart to feel like it's "skipped a beat."

In contrast, the other options describe different cardiac phenomena that do not accurately characterize PACs. A delayed contraction of the ventricle refers to a different type of arrhythmia where ventricular response is not timely, which is not the case with PAC. An extended ventricular rhythm suggests a continuous abnormal rhythm which is not applicable here, as PACs generally do not alter the overall rhythm to that extent. A normal sinus rhythm implies that electrical activity originates from the sinus node without any ectopic rhythms, which does not account for the presence of a PAC.

In conclusion, understanding that PACs indicate an early atrial contraction provides insight into the heart's conduction system and the effects of ectopic pacing within the atria.