Coarctation of the aorta
Coarctation of the aorta (CoA) is estimated to account for 4–6% of
CHDs in newborns, with a reported prevalence of approximately 4 per 10
000 live births28. Congenital coarctation of the aorta
increases impedance to the left ventricular outflow, but this condition
is usually well tolerated by the fetus because the foramen ovale and
ductus arteriosus equalize intracardiac and great arteries pressures and
shunts. Nevertheless, it potentially harbors life-threatening risks if
coarctation is not suspected and the arterial duct closes spontaneously
in postnatal life. This lesion was first described by Morgagni in 1761
and further delineated by Meckel in 1827 with a report on a sudden death
of a 35-year-old peasant who showed a ruptured right atrium beside an
exceedingly thinned aortic lumen with the diameter of a blade of a straw
right beneath the ligamentum aortae during
autopsy29-31. Coarctation of the aorta shows a
considerable variability in its anatomic, physiologic and clinical
characteristics, and chromosomal and extracardiac anomalies are commonly
described. Morphologically, CoA encompasses a marked narrowing of the
ascending aorta and the aortic arch, typically affecting the isthmic
region (between the left subclavian artery and the ductus arteriosus).
Although often found to be a discrete anatomic anomaly, coarctation may
also consist of a long-segment stenosis associated with tubular
hypoplasia of the entire transverse aortic arch (as shown in fig. 1).
The embryologic origin is still not well understood, but CoA is
suggested to most likely result from a manifestation of an abnormality
in the development of the left fourth and sixth aortic arches during
embryogenesis. There are two pathophysiological concepts - according to
a hemodynamic theory, intracardiac lesions, which diminish the volume of
the left ventricular outflow, promote the development of coarctation in
the fetus by reducing flow through the aortic isthmus. In contrast, the
ductus tissue theory assumes that migration of smooth muscle cells into
the aorta leads to subsequent aortic constriction postnatally. The
latter concept is largely based on histological findings of differential
elastic fiber formation between the aorta and ductal
tissue32. Bahado-Singh et al. published on fetal
epigenomic dysregulation of genes involved in both heart development and
postnatal cardiovascular diseases potentially associated with the
pathogenesis of CoA33.
Grayscale ultrasound reveals different degrees of ventricular
disproportions and a larger pulmonary artery than the aorta suspicious
for CoA34,35. Figure 1 clearly depicts these anatomic
changes – an RV-LV discrepancy seen in the 4CV/5CV views and different
diameters of the pulmonary artery compared to the cross-section of the
aorta displayed in the short-axis view of the great vessels/RVOT.
However, most strikingly, the three vessels and trachea view (3VT) shows
a hypoplastic transverse aortic arch, confirming the small ascending
aorta seen in the 5CV/LVOT views. Hornberger et al. described the ratio
of right-to-left ventricular width to be 1.19 in normal fetuses and
greater than 1.69 in those with CoA36. However, an
increased right-to-left ventricular ratio might also be found in other
cardiac conditions such as HLH, DORV, APVS, CDH or Ebstein’s anomaly.
The volumetric approach described herein allows for detailed
reconstruction of additional planes in order to rule out these
differential diagnoses. Color Doppler interrogation may provide
additional information in all diagnostic planes, as described by Yeo and
Romero37.
There is a general consensus that a normal appearance of the sagittal
section of the aortic arch on fetal echocardiography constitutes the
major exclusion criterion for CoA. In the case of coarctation, this view
might depict a posterior shelf or ridge in the aortic wall in addition
to a markedly narrowed aorta (as seen in figure 1). Arya et al. proposed
novel fetal echocardiographic morphometric measures for objective
antenatal assessment of the aortic arch and its branches and found
significant differences in the LCSA, AAo-DAo angle, and Tao-DAo angle
between normal fetuses and those with CoA19. Similar
findings were published by other groups of researchers who found that a
smaller mitral valve diameter, MV to TV ratio, IDD, and isthmus-ductal
angle (IDA), carotid-subclavian artery index (CS) or distal arch index
(DAI) were associated with the development of CoA after
birth38-40. In contrast to HLH, the apex is still
formed by the LV, and the myocardial contractility seems to be normal in
CoA. However, DeVore et al. described the 4CV view to be more spherical
in shape, increased in area and width, and decreased in length during
speckle tracking analysis41. A recent metaanalysis
stated that adoption of multiparametric diagnostic models integrating
different ultrasound signs may assist examiners in identifying fetuses
with CoA. Interestingly, a persistent left superior vena cava, a
ventricular septal defect, and a bicuspid aortic valve were not
associated with an increased risk for this anomaly42.
Acknowledging that these parameters might be helpful in the prenatal
diagnosis of coarctation, one has to admit that precise and reproducible
assessment is strongly operator dependent and inevitably needs different
cardiac planes for an exact calculation of the aforementioned objective
measures. This might partly explain the considerably high number of both
false-positive and false-negative diagnoses and why CoA remains the most
commonly missed ductal-dependent lesion to date.
From a functional perspective, recent data on cardiovascular adaptation
during neonatal life suggest that, despite biventricular remodeling and
cardiac output redistribution, fetuses with CoA have no significant
myocardial dysfunction43. Regarding the postnatal
prognosis of CoA, the variables associated with intervention comprised
smaller AAo and transverse arch size, earlier gestational age at
diagnosis, and the additional finding of a higher peak AAo
Doppler44. Confirmed cases of CoA must be followed
closely over the lifetimes of affected newborns for complications such
as recoarctation, aortic aneurysm, persistent hypertension, and changes
in any associated cardiac defects45.