In a Wenckebach AV block, what is the pattern of P to QRS waves?

In a Wenckebach AV block, what is the pattern of P to QRS waves?

• A. One more QRS complex than P wave
• B. One less QRS complex than P wave
• C. Equal number of P waves and QRS complexes
• D. Two QRS complexes for every P wave

Answer: (B)

In a Wenckebach AV block, also known as Mobitz type I second-degree AV block, there is a distinct pattern involving the relationship between P waves and QRS complexes. The hallmark of this type of block is that the electrical signals from the atria (represented by the P waves) progressively get delayed until one P wave fails to conduct through to the ventricles, resulting in a dropped QRS complex.

This results in a scenario where, for every series of conducted P waves and QRS complexes, there is one fewer QRS complex than P waves. More precisely, you will observe a pattern where you see a few P waves that are followed by QRS complexes, and then one of those P waves will not be followed by a QRS complex at all. Due to this dropping of the QRS after a certain number of P waves, the overall count of QRS complexes will indeed be one less than the count of P waves during the observed cycle.

Thus, the understanding of a Wenckebach AV block is characterized by the progressive lengthening of the PR interval followed by a QRS drop, leading to the outcome where there is one less QRS complex than the number of P waves.