Which statement best describes normal sinus rhythm P waves?

• A. P waves before each QRS are upright and identical
• B. P waves are inverted before QRS
• C. P waves are absent
• D. QRS complexes are wide

Answer: (A)

Normal sinus rhythm starts with the SA node firing in a regular pattern, so the atria depolarize in a uniform way. On the ECG, that shows up as P waves that occur before every QRS complex, reflecting atrial activation followed by ventricular activation. Those P waves should be upright (positive) in standard leads and have the same shape from beat to beat, indicating consistent atrial conduction from beat to beat. If P waves were inverted before the QRS, or if P waves were absent, that would signal an abnormal atrial origin or an atrial arrhythmia. A wide QRS points to a ventricular conduction issue rather than normal sinus rhythm. So, P waves before each QRS that are upright and identical best describe normal sinus rhythm P waves.