[ECG : interpretation and clinical significance of P-wave abnormalities].

The ECG provides information about heart rhythm and myocardial integrity, including the atria. The sinus P wave exhibits a 0‑90° axis and a generally biphasic morphology in lead V1. An amplitude >2 mm in lead II and >1 mm in lead V1 is a specific sign of right atrial enlargement, often related to pulmonary disease or pulmonary hypertension. Interatrial block (IAB) is defined as a P-wave ≥120 ms with, in the advanced form, a biphasic morphology in inferior leads. It is most commonly seen in the context of advanced age, cardiovascular risk factors, coronary artery disease or valvulopathies. IAB is a risk factor for supraventricular tachyarrhythmias, stroke, left ventricular dysfunction and mortality. The identification of a P-wave abnormality has prognostic implications and should trigger the search for associated conditions.