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The normal P wave should be <120ms in duration, <2.5mm in amplitude, and have a relatively convex shape. However, atrial enlargement alters the P wave morphology, either producing a longer duration or a greater amplitude. The initial portion of the P wave represents right atrial activation and the latter portion represents left atrial activation. The P waves are usually best evaluated in leads II and V1.
Right Atrial Enlargement
Right Atrial Enlargement
Right atrial enlargement (RAE) is sometimes referred to as P pulmonale. It produces a greater amplitude within the P wave (prolonged duration would just extend to end of P wave as the normal right atrial duration ends before the P wave actually ends as represented in the above picture). This is because the shifted duration produces a shift in the time of greatest amplitude to combine with the greatest amplitude from the left atrial depolarization. This combination produces a taller P wave (>2.5mm in the inferior leads or >1.5mm in V1) with a normal duration.
Causes of right atrial enlargement:
chronic lung disease
tricuspid stenosis
primary pulmonary hypertension
congenital heart disease that causes right heart strain/hypertrophy (tetralogy of Fallot and pulmonary stenosis)
Examples:
Left Atrial Enlargement
Left Atrial Enlargement
Left atrial enlargement (LAE) is also known as P mitrale. It is defined by a P wave>120ms. This is because the enlargement produces a longer duration at the end of the P wave. Because of this delayed maximum amplitude of the left atrial depolarization, the P wave is frequently notched or has a camelback appearance in the inferior leads.
Left atrial enlargement is often a precursor to atrial fibrillation. The causes are:
mitral stenosis
mitral regurgitation
systemic hypertension
aortic stenosis
hypertrophic cardiomyopathy
Examples:
Biatrial Enlargement
Biatrial Enlargement
This is diagnosed when criteria for both RAE and LAE are met. The P waves are often prolonged, have a high amplitude, and have the camelback appearance in the inferior leads
Examples:
Summary Table
Summary Table
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