P wave

P wave is a term used in Cardiology to describe a specific pattern seen on an Electrocardiogram (ECG). The P wave represents the electrical conduction through the atria, which leads to atrial contraction, or atrial systole.

Overview

The P wave is the first positive deflection on the ECG and is associated with atrial depolarization, which in turn results in atrial contraction. The P wave is usually upright in leads I, II, aVF and V3-V6; inverted in lead aVR; and variable in the other leads.

Characteristics

The normal P wave duration is less than or equal to 0.12 seconds (or 120 milliseconds). The P wave should be smooth, rounded and upright, not notched or pointed, and should be of uniform shape in any given lead. The P wave axis is normally between 0° and +75° in the frontal plane.

Clinical significance

Abnormalities in the P wave can indicate a number of clinical conditions. For example, a P wave duration of more than 0.12 seconds can suggest atrial enlargement, while a biphasic P wave can suggest an atrial septal defect.

See also

• QRS complex
• T wave
• U wave

References

Cardiovascular disease A-Z

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A

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I

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• Right axis deviation
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T

• Traumatic cardiac arrest

V

• Ventricular aneurysm
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W

• Waon therapy

P wave Resources
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