What is normal interatrial septal motion on transthoracic echocardiogram (TTE) apical 4-chamber view?

From the Guidelines

Normal interatrial septal motion on TTE apical 4-chamber view is characterized by minimal movement toward the left atrium during ventricular systole and toward the right atrium during ventricular diastole. This motion is a result of the normal pressure differences between the left and right atria throughout the cardiac cycle. The interatrial septum should appear as a thin, continuous structure with slight bowing that follows the cardiac cycle. During ventricular systole, right atrial pressure slightly exceeds left atrial pressure, causing minimal bowing toward the left atrium. Conversely, during ventricular diastole, left atrial pressure becomes higher than right atrial pressure, resulting in slight movement toward the right atrium.

Key Characteristics of Normal Interatrial Septal Motion

• Minimal movement toward the left atrium during ventricular systole
• Minimal movement toward the right atrium during ventricular diastole
• Slight bowing of the interatrial septum following the cardiac cycle
• The interatrial septum should appear as a thin, continuous structure Abnormal septal motion, such as fixed bowing toward one atrium or excessive mobility, may indicate pathological conditions like elevated atrial pressures or structural abnormalities. Although the provided study 1 focuses on standardization of adult transthoracic echocardiography reporting, including chamber quantification and diastolic function, it does not directly address interatrial septal motion. However, understanding normal cardiac structure and function, as outlined in the study, is essential for identifying abnormalities in interatrial septal motion. When evaluating the interatrial septum, it's crucial to assess both its structure and motion throughout the complete cardiac cycle to identify any abnormalities.

From the Research

Normal Interatrial Septal Motion on TTE Apical 4 Chamber

• The interatrial septum (IAS) is a thin wall of tissue that separates the left and right atria of the heart.
• On a normal TTE apical 4-chamber view, the IAS is typically curved toward the right atrium, with a slight convexity toward the right atrium at end-systole 2.
• The motion of the IAS is influenced by the pressure gradient between the left and right atria, with increased systolic motion of the IAS resulting from an increased systolic left atrial-to-right atrial pressure gradient 3.
• In normal subjects, the interatrial septal amplitude is typically around 9.4 +/- 0.9 mm, as measured by M-mode echocardiogram 3.

Factors Affecting Interatrial Septal Motion

• The interatrial pressure gradient, which is the difference between the pulmonary capillary wedge pressure and the central venous pressure, is a major determinant of interatrial septum shape and motion 2.
• Changes in left atrial size can also affect the degree of interatrial septum curvature, although to a lesser extent than the interatrial pressure gradient 2.
• Mechanical ventilation can cause transient reversals of the interatrial pressure gradient, resulting in a momentary bowing of the interatrial septum toward the left atrium during passive mechanical expiration 2.

Clinical Significance of Interatrial Septal Motion

• Abnormal interatrial septal motion can be an indicator of various cardiac conditions, such as acute mitral regurgitation 3 or atrial septal defects 4.
• Midsystolic reversal of the interatrial septum, which can be observed during mechanical expiration, may be a useful indicator of pulmonary capillary wedge pressure 2.