Makindo Medical Notes

Normal P Wave

• Shape: The P wave should be smooth and rounded in most leads, particularly in leads I and II. A consistent morphology indicates a regular sinus rhythm.
• Duration: The normal P wave lasts between 0.08 to 0.11 seconds (80 to 110 milliseconds). It should not exceed this time frame as it would suggest abnormal atrial conduction.
• Amplitude: The amplitude of the P wave is usually less than 2.5 mm in height in lead II. Amplitude exceeding 2.5 mm is often associated with right atrial enlargement.
• Direction:
  • Positive: The P wave is normally upright (positive) in leads I, II, aVL, and aVF.
  • Negative: In lead aVR, the P wave is normally inverted (negative).
  • Biphasic: In lead V1, the P wave can appear biphasic (with both positive and negative components).
• Physiological Significance: The P wave represents atrial depolarization, primarily reflecting electrical activity originating from the sinoatrial (SA) node and traveling through the atria.

Abnormal P Wave

Abnormality	Cause	Appearance
Peaked P Wave (P Pulmonale)	Typically associated with right atrial enlargement, which occurs due to conditions such as pulmonary hypertension or chronic obstructive pulmonary disease (COPD).	The P wave is tall and peaked, with a height exceeding 2.5 mm in lead II.
Broad, Notched P Wave (P Mitrale)	Associated with left atrial enlargement, often seen in mitral valve disease or left ventricular hypertrophy.	The P wave is wide (longer than 0.12 seconds) and notched, particularly in leads I and II. This results in a "double-humped" or "M-shaped" P wave.
Inverted P Wave	Indicates that the atrial depolarization is occurring in a direction opposite to the normal conduction pathway, usually from a low atrial or ectopic pacemaker. This is common in junctional rhythms or ectopic atrial rhythms.	The P wave is inverted in leads where it should normally be upright (e.g., leads I and II).
Absent P Wave	A missing P wave can indicate atrial fibrillation (AF), where the atria are quivering rather than undergoing coordinated depolarization, or it may be seen in junctional rhythms where the impulse originates from the AV node.	No discernible P waves are present. In atrial fibrillation, the baseline may show irregular fibrillatory waves instead.
Prolonged P Wave Duration	A P wave lasting longer than 0.12 seconds is often indicative of left atrial enlargement or delayed conduction between the atria, such as in interatrial block.	The P wave appears prolonged, especially in leads I and II.
Varying P Wave Morphology (Multifocal Atrial Tachycardia)	In multifocal atrial tachycardia (MAT) or wandering atrial pacemaker, multiple ectopic pacemakers in the atria lead to varying P wave shapes, reflecting different origins of atrial depolarization.	P waves vary in size, shape, and direction, with at least three distinct morphologies noted in different beats.
P Wave Axis Deviation	An abnormal P wave axis (outside the normal range of 0° to +75°) can suggest underlying pathology, such as right or left atrial enlargement or conduction abnormalities.	Abnormal axis results in P wave inversion in leads that should normally show positive deflections.

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