P wave | Case-based insights: ECG

The P wave provides important information about the state of the atrial myocardium. A flat, broadened P wave (>120 ms, P sinistroatriale) indicates left atrial damage, usually in hypertension, often in cardiac failure and mitral defects. A narrow, high P wave (>0.25 mV, P dextroatriale) indicates pulmonary disease or congenital vitiation. A P biatriale (P wave >120 ms and >0.25 mV) usually indicates severe global cardiac failure or a combination of cardiac failure and pulmonary disease. A flat, broad, double-peaked or even triphasic P wave is indicative of an interatrial conduction defect, e.g., fibrosis of the septum. A terminally negative P wave in lead II indicates left-atrial excitation from caudal to cranial, which may be associated with atrial fibrillation and left-atrial atrial flutter. A P wave negative in lead II is found in cases of ectopic rhythm from the deep atrium and may indicate atrial damage in electrolyte disturbances or myocarditis. In junctional rhythms, the P wave is usually hidden in the QRS complex. A “wandering pacemaker” is an ECG at rest with ≥3 distinct P wave morphologies (no supraventricular extrasystoles) on a single ECG sheet (12 s). This may be due to severe atrial myocardial damage, electrolyte disturbances, or hyperthyroidism.