NORMAL CARDIAC AXIS

At about 8 menstrual weeks the fetal heart rotates around both a horizontal and vertical axis from the right to left chest. This results in the right ventricle finishing as the anterior chamber.

MEASUREMENT

The cardiac axis is measured on the 4-chamber view of the heart. The normal cardiac axis is obtained by measuring the angle between:

1. A line is drawn through the fetal spine and sternum dividing the thorax into two equal halves.
2. A second line is drawn through the interventricular septum and is projected anteriorly where the interventricular septum bisects the anterior chest wall, and posteriorly dividing the atria to a point at the base of the heart. The position of this point determines the cardiac position. The heart may be positioned abnormally in the right thorax and still have a normal axis.

Normal axis = 45 ± 20° (2 standard deviations).
Normal range = 22°-75° (1).

3. Levardia: The cardiac apex points to the left (normal).

4. Mesordia: The cardiac apex points to the midline.

5. Dextrocardia: The cardiac apex points to the right

REFERENCES

1. Comstock CH. Normal fetal heart axis and position. Obstet Gynecol 1987;70:255-259.