page_title: P wave (electrocardiography)
section_title: Pathology
hierarchical_section_title: P wave (electrocardiography) / Pathology
context_page_description: The P wave on the ECG represents atrial depolarization, which results in atrial contraction, or atrial systole.
context_section_description: Peaked P waves (> 0.25 mV) suggest right atrial enlargement, cor pulmonale, (P pulmonale rhythm), but have a low predictive value (~20%). 
  A P wave with increased amplitude can indicate hypokalemia. It can also indicate right atrial enlargement.
  A P wave with decreased amplitude can indicate hyperkalemia.
  Bifid P waves (known as P mitrale) indicate left-atrial abnormality - e.g. dilatation  or hypertrophy.
  If at least three different shaped P waves can be seen in a given ECG lead tracing, this implies that even if one of them arises from the SA node, at least two others are arising elsewhere.  This is taken as evidence of multiple (i.e. at least two) ectopic foci, and is called multifocal (or more correctly, multiform) atrial rhythm if the rate is ≤100) or multifocal atrial tachycardia if the rate is over 100.  This appears particularly commonly in exacerbations of chronic obstructive lung disease.
  If the baseline has a totally irregular form, this suggests fibrillatory waves of atrial fibrillation or possibly artefact; a saw tooth shaped baseline suggests the flutter waves of atrial flutter.  With either of these rhythms, if the ventricular rate is fast, the fibrillatory or flutter waves can easily be misinterpreted as P waves.
  Absence of the P wave with a flat baseline may indicate:
  Fine atrial fibrillation
  Sinoatrial arrest (with a secondary escape rhythm)
  If P waves are not clearly delineated in the surface ECG, a Lewis lead may be used to better visualize P waves.
caption: P-wave changes in left and right atrial hypertrophy
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