Fetal echocardiography: state of the art of the state of the heart

Ultrasonographic evaluation of the fetal thymic-thoracic ratio and its association with conotruncal heart defects

OBJECTIVE

To evaluate the thymic-thoracic ratio (TT ratio) on fetal ultrasound and its association with conotruncal heart defects.

METHODS

A case control study was carried out to retrospectively assess the TT ratio on fetal echocardiograms performed between 19 and 39 weeks of gestation, showing congenital heart defects, from January to December 2018. The control group was comprised of fetuses with no echocardiogram evidence of congenital cardiac malformations. Cases of multiple pregnancies and patients where the TT ratio could not be established have been excluded.

RESULTS

A total of 338 pregnancies have been analysed. Fifty-two pregnancies were diagnosed with fetal heart defects (15%), 17 of which showed conotruncal heart defects (32.7%). The TT ratio in normal fetuses (286 pregnancies) increased with gestational age, and had an average of 0.43 ± 0.06. Compared to the control group (normal fetuses), fetuses with conotruncal heart defects had significantly lower mean TT ratio (0.33 ± 0.07). Those that were diagnosed with nonconotruncal heart defects did not show any statistically significant difference in the TT ratios compared with the control group (0.40 ± 0.09 vs. 0.43 ± 0.06, respectively).

CONCLUSION

The TT ratio was significantly lower in fetuses with conotruncal heart defects compared with both the control group (normal fetuses) and the fetuses with nonconotruncal heart defects.

The thymic-thoracic ratio in fetal heart defects: a simple way to identify fetuses at high risk for microdeletion 22q11

OBJECTIVES

To establish reference ranges for the fetal thymic-thoracic ratio (TT-ratio) and to compare results with those from fetuses with congenital heart defects (CHD) with and without microdeletion 22q11 (del.22q11), a condition known to be associated with a hypoplastic thymus.

METHODS

TT-ratio was defined as the quotient of the anteroposterior thymic to the intrathoracic mediastinal diameters measured in the three vessels and trachea view. This ratio was measured in a prospective cross-sectional study of 302 normal healthy fetuses between 15 and 39 weeks' gestation. The study group comprised two groups: one group (CHDn) consisted of 90 fetuses with CHD and a normal karyotype with no del.22q11 and the other group (CHD(22)) included 20 fetuses with CHD and a normal karyotype but with proven del.22q11.

RESULTS

The TT-ratio of the normal fetuses did not show any statistically significant change during gestation, with a mean value of 0.44. The values of all 90 fetuses of the CHDn group were within the normal range and no different from normal fetuses. However, 19 of the 20 (95%) fetuses in the CHD(22) group had a significantly smaller TT-ratio (P < 0.001) compared with both the CHDn group and the normal fetuses, having a mean value of 0.25.

CONCLUSIONS

The TT-ratio is reliable and easy to obtain during fetal echocardiography. Fetuses with CHD and a low TT-ratio can be considered at high risk of having microdeletion del.22q11.

New developments in fetal heart scanning: three- and four-dimensional fetal echocardiography

This article reviews the possibilities of three- and four-dimensional (3- and 4D) fetal echocardiography. A volume data set of a fetal heart can be acquired as a static volume, as a real-time 3D volume or as an offline 4D volume cine using spatial and temporal image correlation (STIC) software. STIC is explained and the potentials of this modality are emphasized. The display of a fetal heart volume data set demonstrates the cross-sections of interest, using the multiplanar mode or tomographic multislice imaging, and different volume rendering tools. The latter include: surface, minimum, inversion and glass body modes. This review highlights the potential of acquiring a digital volume data set of a heart cycle for later offline evaluation, either for an offline diagnosis, a second opinion (e.g. via Internet link) or for teaching fetal echocardiography to trainees and sonographers.

Ductus venosus Blood Flow Velocity Waveforms as a Predictor for Fetal Outcome in Isolated Congenital Heart Disease

OBJECTIVE

To investigate whether pulsatility of ductus venosus (DV) flow velocity waveforms is of diagnostic value in predicting survival in fetuses with congenital heart disease (CHD).

METHODS

In a cross-sectional study, Doppler investigation of DV and umbilical artery blood flow was performed in 58 fetuses with isolated structural CHD, without other sonographically detectable structural or chromosomal abnormalities or tachyarrhythmia. The pulsatility index for veins of DV (DV-PIV) waveforms was expressed as multiples of the 95th centile (Mo95th) of the reference ranges for gestational age. The PIV was related to intrauterine and neonatal mortality within the first 6 months of life. Terminations of pregnancies and neonates with additional abnormalities detected after birth were excluded from statistical analysis. For statistical analysis, the different types of heart defects were separated into atrial and/or ventricular (AV) septal defects, right or left ventricular in- and outflow tract abnormalities and others.

RESULTS

After exclusion of 9 pregnancies (2 cases with failure of measurements of DV-PIV, 2 neonates with additional malformations, and 5 terminations of pregnancies), 49 cases were available for statistical analysis. The umbilical artery pulsatility index was within normal ranges in all but 1 case with AV canal and hydrops. In 7 pregnancies intrauterine fetal deaths occurred and 6 of them were hydropic. The median gestational age at birth for liveborn neonates was 39.0 weeks (range 27.8-41). There were 6 postnatal deaths, all but 1 within 28 days of delivery. The remaining fetuses survived for at least 6 months. The overall mortality rate was 27% (13/49). The DV-PIV was significantly higher in non-survivors than in survivors (median of Mo95th and interquartile ranges 1.48 (1.04-1.95) vs. 0.81 (0.70-1.15); p = 0.01). Analysis of subgroups showed significant differences for AV septal defects and abnormalities affecting predominantly the right ventricle (p = 0.046 and 0.043, respectively). Ten out of 13 non-survivors showed an abnormal DV-PIV (sensitivity 77%) as compared to 12 out of 36 survivors (specificity 67%). All hydropic fetuses (n = 6) showed an abnormal DV-PIV and ended in intrauterine deaths.

CONCLUSIONS

Evaluation of the DV pulsatility is a useful additional variable for predicting the risk for mortality in fetuses with isolated structural CHD, in particular in fetuses with defects of the AV septum and with defects affecting predominantly right ventricular function. As there is no fetal hydrops without abnormal DV, this is another sign for the association of DV and cardiac failure.

Spatio-temporal image correlation (STIC): a new tool for the prenatal screening of congenital heart defects

OBJECTIVE

To assess the feasibility and capability of STIC acquisition, performed by a general obstetrician performing antenatal ultrasound, to visualize fetal cardiac structures in women undergoing routine obstetric ultrasound examination, in order to obtain information to confirm normality of the fetal heart during intrauterine life.

METHODS

This was a prospective study of one hundred fetuses with echocardiographically confirmed normal hearts and no extracardiac anomalies with gestational ages ranging between 18 and 37 weeks. A general obstetrician was invited to acquire the STIC volumes. The four-chamber view was obtained as a starting point. A standard 7.5-s acquisition time and 30 degrees angle of acquisition were used and the resulting STIC was stored for later offline analysis by a fetal echocardiologist. For each patient, the stored STIC data were first evaluated by sweeping from the initial acquisition plane, in the caudal direction and then cranially, zooming, slowing or stopping the cardiac motion to visualize views and structures. If a structure or view was rated as inadequate or not identifiable, a multiplanar three-dimensional (3D) examination of the STIC volume was taken in order to try to visualize it adequately. The rates obtained using just the STIC sweeps were compared independently, and then the 3D multiplanar study was added.

RESULTS

STIC acquisition was possible in all cases. The mean time required for STIC acquisition was 7.5 min. A complete cardiac examination according to the set criteria was achieved in 94.2% (95% confidence interval (CI), 90-99) of cases. We obtained a 94.2% success rate of visualizing different structures and views of the fetal heart using the STIC sweep alone (95% CI, 90-99) and 96.2% adding 3D multiplanar examination (95% CI, 92-100).

CONCLUSION

STIC acquisition of the fetal heart is feasible with high success rates in visualization of the principal connections. The STIC data acquired by a general obstetrician can subsequently be used by a fetal echocardiologist for prenatal confirmation of normal cardiac structure or exclusion of major cardiac malformations.

Three cross-sectional planes for fetal color Doppler echocardiography

Routine use of color Doppler during every fetal cardiac examination remains controversial. Many examiners still believe that color should be reserved for cases of suspected congenital heart defect (CHD). In our opinion, color Doppler should be applied in every cardiac scan due to the increase in speed and accuracy that it allows. The purpose of this review is to first explain how color Doppler presets can be optimized and, second, to propose the use of three cross-sectional planes to simplify color Doppler fetal echocardiography: the four-chamber (4CV), five-chamber (5CV) and three-vessel (3VV) views. A practical approach to the detection of CHD with these planes is presented, with typical findings and possible abnormalities evident during systole and diastole. The diastolic pattern on the 4CV is characterized by two equal color stripes. Connection ('H'-sign) or size inequality of the two stripes, or a unilateral color stripe, are important abnormal findings. In systole valve regurgitation should be excluded. In the 5CV, turbulent flow, ventricular septal defect or an overriding aorta ('Y'-sign) can be detected. In the 3VV the aorta and pulmonary trunk should be of nearly equal size and demonstrate antegrade flow. Abnormal findings encountered include absence of one vessel, discrepant size of the vessels, retrograde flow in one of the vessels, or the 'U'-sign, where the trachea is enclosed between both vessels, suggesting right-sided aortic arch. In summary, we propose that color Doppler examination utilizing these three planes alone is sufficient to obtain adequate information for the detection of most common CHD.

Absent or hypoplastic thymus on ultrasound: a marker for deletion 22q11.2 in fetal cardiac defects

OBJECTIVE

Congenital heart defects (CHD), particularly conotruncal anomalies, may be associated with deletion of chromosome 22q11.2. Thymic aplasia or hypoplasia is known to be a typical feature in this condition. We aimed to establish (i) the prevalence of del22q11.2 in fetal CHD and (ii) whether ultrasound assessment of an absent or hypoplastic fetal thymus helps in preselection of a group who are at high risk for this deletion.

STUDY DESIGN

In fetuses (> 16 weeks) with CHD, karyotyping and fluorescence in situ hybridization for 22q11.2 were offered and the fetal thymus was evaluated sonographically.

RESULTS

One hundred and forty-nine fetuses with CHD and normal karyotype were analyzed. Seventy-six fetuses had conotruncal anomalies. 22q11.2 deletion was present in 10 cases (6.7%), all of which had conotruncal anomalies (13.1%). Thymic hypoplasia or absence was suspected in 11 cases with conotruncal anomaly. Nine of these 11 had the deletion; two cases were false positive. One fetus with a normal-sized thymus had deletion of 22q11.2 (sensitivity 90%, specificity 98.5%, positive predictive value 81.8%, and negative predictive value 99.2%). By subtype of cardiac anomaly, there was deletion in four of six fetuses with interruption of the aortic arch, two of four with absent pulmonary valve syndrome, three of nine with truncus arteriosus and one of 11 cases of tetralogy of Fallot. Pulmonary atresia with ventricular septal defect (n = 7), right-sided aortic arch (n = 4), transposition of the great arteries (n = 14), double outlet right ventricle (n = 13) and other complex malpositions of the great vessels (n = 8) were not associated with the deletion.

CONCLUSION

Thymic hypoplasia or aplasia may reliably be diagnosed during fetal echocardiography. The technique allows identification of a group at high risk for 22q11.2 deletion and is more specific and sensitive than by subtype of cardiac anomaly alone.

Real-time three-dimensional fetal echocardiography--optimal imaging windows

A total of 15 fetuses were scanned using 2-D array volumetric ultrasound (US). Acquired cardiac data were converted for rendering dynamic 3-D surface views and reformatting cross-sectional views. The image usefulness was compared between the data obtained from subcostal/subxiphoid and other imaging windows; the former are usually free of acoustic shadowing. Of 60 data sets recorded, 12 (20%) were acquired through subcostal windows in 6 (40%) patients. Subcostal windows were unavailable from the remaining patients due to unfavourable fetal positions. Of the 12 sets, 6 (50%) provided the dynamic 3-D and/or cross-sectional views of either the entire fetal heart or a great portion of it for sufficient assessments of its major structures and their spatial relationships. Of 48 data sets from other windows, only 9 (19%) provided such 3-D and/or cross-sectional views; the lower rate being due to acoustic shadowing. Real-time 3-D US is a convenient method for volumetric data acquisition. Through subcostal windows, useful information about the spatial relationships between major cardiac structures can be acquired. However, to offer detailed information, considerable improvement in imaging quality is needed.

Prenatal detection of ductal-dependent congenital heart disease: how can things be made easier?

OBJECTIVE

To improve the detection of ductal dependence in fetuses with severe anomalies of the outflow tracts by observing, with directional power Doppler, reverse flow through the aortic arch or ductus arteriosus in a transverse view of the upper mediastinum.

METHODS

A slight cranial move of the ultrasound beam from the three-vessel view allows the transverse view of the aortic arch and ductus arteriosus to be visualized simultaneously. This view is orthogonal to the fetal body axis and parallel to the plane of the four-chamber view. In normal fetuses, directional power Doppler interrogation at this level identifies forward flow in both oblique vessels.

RESULTS

We examined 43 fetuses with cardiac defects. In five of the cases, there was reversed flow in the aortic arch or ductus arteriosus in addition to severe anomalies of the outflow tracts, including four with hypoplastic left ventricle and one with pulmonary atresia.

CONCLUSIONS

Prenatal detection of reversed flow in the aortic arch or ductus arteriosus is associated with complex congenital heart disease with major diminution of forward flow to the corresponding great vessels.