[P-wave pattern].

The analysis of atrial rhythm is a fundamental step in the interpretation of a resting electrocardiogram. Careful identification of P waves is essential; however, their presence alone does not necessarily indicate sinus rhythm. A systematic assessment of P-wave morphology and axis, as well as a focused search for non-conducted P waves, is crucial for accurate classification of the underlying cardiac rhythm. Ectopic atrial rhythms, atrial tachycardias, and atrial flutter typically exhibit P-wave patterns that differ from those seen in normal sinus rhythm. Normal sinus rhythm originates in the region of the superior vena cava and propagates from right to left and from cranial to caudal across both atria. The present case highlights common diagnostic pitfalls in a patient with clearly discernible P waves.