In sinus rhythm, how do P waves relate to QRS complexes?

In sinus rhythm, how do P waves relate to QRS complexes?

• A. One P wave precedes each QRS and P waves are upright and uniform
• B. P waves may precede only some QRS complexes
• C. P waves are inverted before QRS
• D. P waves precede multiple QRS or none

Answer: (B)

In sinus rhythm, the impulse starts in the sinoatrial node and atrial depolarization shows up as a P wave that precedes every ventricular depolarization represented by a QRS complex. So you should see one P wave before each QRS, and the P waves should be upright and uniform with a constant PR interval. If you ever think a P wave only sometimes precedes a QRS, that would suggest non-sinus conduction or another rhythm pattern, not true sinus rhythm. Keep in mind that in some tracing situations a P wave can be faint or obscured (hidden in the preceding T wave or drowned by rapid heart rates), but the underlying pattern in sinus rhythm is that a P wave precedes each QRS complex.

In sinus rhythm, the impulse starts in the sinoatrial node and atrial depolarization shows up as a P wave that precedes every ventricular depolarization represented by a QRS complex. So you should see one P wave before each QRS, and the P waves should be upright and uniform with a constant PR interval. If you ever think a P wave only sometimes precedes a QRS, that would suggest non-sinus conduction or another rhythm pattern, not true sinus rhythm. Keep in mind that in some tracing situations a P wave can be faint or obscured (hidden in the preceding T wave or drowned by rapid heart rates), but the underlying pattern in sinus rhythm is that a P wave precedes each QRS complex.