What is the defining characteristic of a premature atrial beat (PAB) on an EKG?

What is the defining characteristic of a premature atrial beat (PAB) on an EKG?

• A. An inverted P wave following a QRS complex
• B. A P wave appearing earlier than expected
• C. A QRS complex wider than normal
• D. A distinct pause before the next beat

Answer: (B)

The defining characteristic of a premature atrial beat (PAB) on an EKG is that a P wave appears earlier than expected. This early P wave indicates that the beat originated from an ectopic focus in the atria, rather than the normal sinus node. The presence of this early atrial depolarization is the hallmark of PABs.

In terms of timing, the P wave will still be followed by a QRS complex unless there is an accompanying conduction block. This characteristic can help distinguish PABs from other arrhythmias, as the interval from the previous beat is shortened due to the premature nature of the atrial contraction. Identifying such early P waves is crucial for correctly diagnosing and interpreting the rhythm on an EKG.

In contrast, while an inverted P wave after a QRS complex can indicate various types of ectopic or junctional rhythms, it does not specifically define a premature atrial beat. A wide QRS complex typically suggests a ventricular-origin beat or conduction abnormality, which is inconsistent with the characteristics of a PAB. Lastly, a distinct pause before the next beat is generally associated with compensatory pauses after a premature beat, but this is not a defining feature of PABs themselves. Instead