In a rhythm with complete heart block, what is observed regarding the relationship between P waves and QRS complexes?

• A. They have no fixed relationship; P waves and QRS occur independently
• B. P waves are absent
• C. QRS complexes follow P waves with a constant PR interval
• D. P waves occur only during QRS complexes

Answer: (A)

In complete heart block, the atria and ventricles beat independently, a situation called AV dissociation. The atria keep their own pace driven by the sinus node, so P waves appear regular, while the ventricles are paced by an intrinsic escape rhythm below the block, producing QRS at a slower, separate rate. Because the conduction from the atria to the ventricles is blocked, there is no fixed relationship between P waves and QRS complexes—the timing between a P wave and the next QRS is not constant, and the PR interval varies. The QRS appearance (narrow or wide) depends on where the escape rhythm originates, but the hallmark is that P waves and QRS complexes do not correlate in a fixed way.