Atrial Enlargement and Hypertrophy

 

Objectives:

• The Normal P wave
• Right Atrial Enlargement
• Left Atrial Enlargement

The Normal P wave

• Normal sinus rhythm: The sinus node is the origin of the normal impulse. The normal sinus P wave has the following features.
• Frontal plane:
• Axis: The axis of the normal P wave is approximately +45° to +60° . Thus, the P wave is upright in lead II. This is the most important lead in recognizing that the rhythm is normal sinus. If the P wave is not upright in lead II, the P wave is probably ectopic (not of sinus node origin).
• Contour: The normal P wave is smooth and well-rounded and should not be peaked or notched.
• Amplitude: The normal P wave is =< 2.5 mm in height. The tallest P wave is usually recorded in the lead II.
• Duration: The normal P wave is =<2.5 mm wide or =<100 milliseconds in duration.

• Horizontal plane:
• Sinus P waves are normally upright in V3 to V6. In V1 and often in V2, the contour of the normal P wave may be upright, inverted, or biphasic. Biphasic means that the initial portion of the P wave is upright, and the terminal portion is inverted. The inverted portion should measure  1 mm in duration and  1 mm in depth.

Right Atrial Enlargement

• Frontal plane:
• Axis: When there is right atrial enlargement, the right atrium enlarges downward and to the right, thus the axis of the P wave is shifted vertically to the right of  +60°. Thus, the P waves are tall in leads II, III, and aVF. The P waves in lead III are usually taller than in lead I (P3 >P1).
• Contour: The contour of the P wave is peaked and pointed. These changes are often described as “P-pulmonale” because right atrial enlargement is frequently caused by pulmonary disease.
• Amplitude: The height or amplitude of the P wave increases to >2.5 mm. These P wave changes are best seen in leads II, III, and aVF.
• Duration: The total duration of the P wave is not prolonged unless the left atrium is also enlarged. Because the right atrium is activated earlier than the left atrium, any delay in the propagation of the impulse from the enlargement of the right atrium will coincide with the activation of the left atrium.

• Horizontal plane: In V1, there may not be any significant P wave changes. The P wave remains normally upright, biphasic, or inverted. The initial upright portion may be slightly peaked or pointed or it might be slightly taller than normal, although the terminal portion representing left atrial activation is not affected.

Why is the duration of P wave not prolonged in RAE?

• Because the right atrium is activated earlier than the left atrium, any delay in the propagation of the impulse from enlargement of the right atrium will coincide with the activation of the left atrium.

Direction of RAE

• In the frontal plane, the right atrium enlarges downward and to the right causing a shift in the P wave axis to the right (from arrow 1 to arrow 2). This also leads to taller P waves in lead III than lead I.
• In the horizontal plane, the enlargement of the right atrium is slightly anterior, which may cause slight peaking of the P waves in lead V1. The shaded portion indicates the changes that occur when the right atrium enlarges.

EKG FINDINGS OF RAE

• The P waves are tall and peaked, measuring > 2.5 mm in leads II, III, or aVF.
• The duration of the P wave is not increased unless the left atrium is also enlarged.

Left Atrial Enlargement

The ECG changes of left atrial enlargement are best reflected in the terminal half of the P wave because the right atrium is activated earlier than the left atrium. 

• Frontal plane:
• Axis: The axis of the P wave is shifted to the left, thus the P waves are taller in lead I than in lead III (P1 >P3).
• Contour: The contour of the P wave is bifid or “M” shaped. The first hump represents activation of the right atrium and the second hump represents activation of the left atrium. These two humps are separated by at least one small block and are best seen in leads I, II, aVF, V5, and V6. This type of P wave is often called “P-mitrale,” indicating that at some time in the past, mitral stenosis is the most common cause of left atrial enlargement.
• Amplitude: The height or amplitude of the P wave is not significantly increased.
• Duration: The duration or width of the P wave is increased and should measure  >2.5 mm (>100 milliseconds).

• Horizontal plane: In lead V1, the P wave is biphasic or inverted. The inverted portion measures =>1 mm in depth and =>1 mm (0.04 seconds) in duration.

Direction of LAE

• The left atrium enlarges to the left and posteriorly shifting the P wave axis to the left of +45°, becoming more horizontal at 20° to 40° . The P wave abnormalities are best seen in leads I, II, aVF and V1. P wave in lead I is taller than the P wave in lead III (P1>P3). Because activation of the atria is sequential, starting from right atrium to left atrium, the duration of the P wave is prolonged. The P waves are not only wide but are notched in leads I, II, and aVF. The terminal portion is inverted in lead V1.

EKG FINDINGS OF LAE

• The duration of the P wave is increased in leads I, II, or aVF. The P waves are often notched with M shape pattern measuring >2.5 mm in width or >100 milliseconds in duration.
• Terminally inverted P waves in V1 measuring =>1 mm in depth and =>1 mm in duration.

Biatrial Enlargement

When both atria are enlarged, the criteria for right atrial and left atrial enlargement are both present because the atria are activated separately.

• Frontal plane: In the frontal plane, the P waves are tall measuring >2.5 mm because of right atrial enlargement. At the same time, the P waves are broad, notched, or M-shaped measuring >2.5 mm wide from left atrial enlargement. These changes are best seen in leads I, II, and aVF.

• Horizontal plane: In the horizontal plane, the P wave in V1 is biphasic or inverted. The initial positive portion is usually peaked due to right atrial enlargement and the terminal negative portion is =>1 mm wide and =>1 mm deep from left atrial enlargement.

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