Objective: To evaluate the use of the cardiac axis within the chest for the prenatal detection of congenital heart defects.
Methods: We reviewed retrospectively the sonographic findings of all fetuses scanned between 17 and 40 weeks' gestation and diagnosed prenatally as having heart defects. The cardiac diagnoses were confirmed postnatally. The control group consisted of 75 consecutive fetuses with normal fetal surveys and newborn follow-up examinations. The cardiac axes were measured retrospectively using an image of the four-chamber view of the heart and measuring the angle between the interventricular septum and a line bisecting the chest. Mean and standard deviations (SDs) of the axis measurements in normal and abnormal fetuses were compared by Student t test.
Results: The 75 fetuses with heart defects diagnosed by prenatal sonogram had a mean cardiac axis of 56 +/- 13 degrees, compared with 43 +/- 7 degrees in normal fetuses (P < .001). Using 57 degrees (two SDs above the mean for normal fetuses) as the upper limit of normal, 33 of 75 (44%) abnormal fetuses versus none of 75 normal fetuses were identified. The frequency of cardiac rotation was greater in fetuses with truncus arteriosus, Ebstein's anomaly, pulmonic stenosis, coarctation of the aorta, and tetralogy of Fallot.
Conclusion: The presence of a cardiac axis exceeding 57 degrees in the fetal chest is associated with a substantial risk of congenital heart defects. The finding of an abnormal axis should prompt further evaluation of the fetal heart.