Normal values of cardiac axis (CA) measurements in healthy fetuses during the first trimester screening ultrasound

Cardiac Axis in Early Gestation and Congenital Heart Disease

Congenital heart defects represent the most common structural anomalies observed in the fetal population, and they are often associated with significant morbidity and mortality. The fetal cardiac axis, which indicates the orientation of the heart in relation to the chest wall, is formed by the angle between the anteroposterior axis of the chest and the interventricular septum of the heart. Studies conducted during the first trimester have demonstrated promising outcomes with respect to the applicability of cardiac axis measurement in fetuses with congenital heart defects as well as fetuses with extracardiac and chromosomal anomalies, which may result in improved health outcomes and reduced healthcare costs. The main aim of this review article was to highlight the cardiac axis as a reliable and powerful marker for the detection of congenital heart defects during early gestation, including defects that would otherwise remain undetectable through the conventional four-chamber view.

Semi-Automatic Measurement of Fetal Cardiac Axis in Fetuses with Congenital Heart Disease (CHD) with Fetal Intelligent Navigation Echocardiography (FINE)

Congenital heart disease (CHD) is one of the most common organ-specific birth defects and a major cause of infant morbidity and mortality. Despite ultrasound screening guidelines, the detection rate of CHD is limited. Fetal intelligent navigation echocardiography (FINE) has been introduced to extract reference planes and cardiac axis from cardiac spatiotemporal image correlation (STIC) volume datasets. This study analyses the cardiac axis in fetuses affected by CHD/thoracic masses (n = 545) compared to healthy fetuses (n = 1543) generated by FINE. After marking seven anatomical structures, the FINE software generated semi-automatically nine echocardiography standard planes and calculated the cardiac axis. Our study reveals that depending on the type of CHD, the cardiac axis varies. In approximately 86% (471 of 542 volumes) of our pathological cases, an abnormal cardiac axis (normal median = 40-45°) was detectable. Significant differences between the fetal axis of the normal heart versus CHD were detected in HLHS, pulmonary atresia, TOF (p-value < 0.0001), RAA, situs ambiguus (p-value = 0.0001-0.001) and absent pulmonary valve syndrome, DORV, thoracic masses (p-value = 0.001-0.01). This analysis confirms that in fetuses with CHD, the cardiac axis can significantly deviate from the normal range. FINE appears to be a valuable tool to identify cardiac defects.

Utility of fetal cardiac magnetic resonance imaging in assessing the cardiac axis in fetuses with congenital heart disease

BACKGROUND

Fetal dedicated echocardiography is the standard to measure the fetal cardiac axis. However, fetal screening ultrasound (US) or fetal dedicated echocardiography may be technically limited.

OBJECTIVE

The purpose of this study was to explore the accuracy of fetal cardiac magnetic resonance imaging (MRI) to measure the cardiac axis in fetuses with congenital heart disease as an adjunct to fetal dedicated echocardiography and to assess the predictive value of fetal cardiac MRI measurements in distinguishing healthy fetuses from fetuses with congenital heart disease.

MATERIALS AND METHODS

This is a retrospective study of fetuses referred to our hospital for a fetal cardiac MRI from November 2019 to December 2021. Cardiac axes were measured in the 4-chamber view of the fetal heart using fetal cardiac MRI and dedicated echocardiography, or only using fetal cardiac MRI when screening US was technically limited. The fetuses were divided into a congenital heart disease group and a healthy control group. We used Bland-Altman analysis and the intraclass correlation coefficient (ICC) to assess the agreement of cardiac axis measurements in fetuses with congenital heart disease obtained by cardiac MRI and by fetal dedicated echocardiography. Receiver operating characteristic (ROC) curve analysis of the fetal cardiac axes in the congenital heart disease and healthy fetus groups assessed the predictive value of the cardiac axis measurements.

RESULTS

This retrospective study included 431 women (162 carrying fetuses with congenital heart disease, 269 carrying healthy fetuses). Cardiac axes were measured in the 162 fetuses with congenital heart disease using fetal cardiac MRI and dedicated echocardiography. Cardiac axes were measured in the 269 healthy control fetuses using fetal cardiac MRI when fetal screening US was technically limited. The interobserver analysis and intraobserver analysis showed that the cardiac axis measured by fetal cardiac MRI and fetal dedicated echocardiography was repeatable (ICC>0.90). In 162 fetuses with congenital heart disease, Bland-Altman analysis showed a strong agreement between cardiac MRI and fetal dedicated echocardiography measurements for the cardiac axis. The ICC for the cardiac axis values between cardiac MRI and fetal dedicated echocardiography measurements was 0.99. In fetuses with congenital heart disease, 64.2% (104/162) had an abnormal cardiac axis. For the fetal cardiac axis in both the 162 fetuses with congenital heart disease and the 269 healthy fetuses, the area under the ROC curve reached 0.85 (95% confidence interval: 0.80-0.89; P<0.0001).

CONCLUSION

The cardiac axis can be accurately measured using fetal cardiac MRI when fetal dedicated echocardiography/fetal screening US is technically limited. The cardiac axis measurements by fetal cardiac MRI are consistent with known cardiac axis measurements by fetal dedicated echocardiography. The frequency of abnormal cardiac axis depends on the type of congenital heart disease.