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Page 32 of 43 Rao. Vessel Plus 2022;6:26 https://dx.doi.org/10.20517/2574-1209.2021.93

Doppler studies. Doppler flow velocity recordings across the pulmonary and sub-pulmonary region will
help assess the degree of PS. In subjects with transposition, the dimension of the bulbo-ventricular foramen
and evidence for obstruction across it should be scrutinized. Such obstructions may exist at the time of
presentation, develop later during the natural process of growth or may develop following pulmonary artery
banding . Aortic coarctation [Figure 27] may be seen in some of these patients.
[43]

INTERRUPTED AORTIC ARCH
Aortic arch interruption is characterized as a total absence of luminal communication amongst the
ascending and descending portions of the aorta. This is in contradistinction to aortic coarctation, in which
there is usually a luminal connection [4,22,44] . This lesion comprises less than 1% of all heart defects. Three
[45]
forms of the interrupted aortic arch (IAA) have been designated : (1) Type A. The aortic arch interruption
is located past the left subclavian artery; (2) Type B. The arch interruption occurs in-between the left
common carotid and left subclavian arteries; and (3) Type C. The arch interruption is in-between the right
innominate and left common carotid arteries. Type B interruption is the utmost frequent, consisting of 52%
of IAA cases. Type A interruption is the next most frequent, accounting for 44% of cases. Type C
interruption is least frequent, occurring in only 4% of cases. IAA occurs irrespective of where the aortic arch
descends, i.e., left or right. IAA is generally seen with other heart defects. PDA is the most common among
these, providing continuousness in-between the PA and the descending portion of the aorta. VSDs are seen
in nearly 80% of Type B IAA cases while it is present in only 50% of babies with Type A interruption. Valvar
and subvalvular aortic stenosis, truncus arteriosus, DORV of the Taussig-Bing type, single ventricle (DILV),
TGA, and aorto-pulmonary window are also seen in patients with IAA. A strong connection with
DiGeorge’s syndrome (chromosome 22q11 microdeletion) has been observed, particularly with Type B
interruption.

Two-dimensional echocardiographic and color Doppler studies from supra-sternal notch view usually
[46]
confirm [Figure 60] the diagnosis. MRI studies and angiography are not usually necessary to establish a
diagnosis.

Because of high association with VSD, a careful review of parasternal, apical and subcostal views should be
undertaken to assess the size, location and shunt across the VSD. Since valvar and subvalvular aortic
stenosis, truncus arteriosus, DORV of the Taussig-Bing type, DILV, TGA, and aorto-pulmonary window
are observed in subjects with IAA; these defects should be excluded during the echo-Doppler study.

PULMONARY ATRESIA WITH INTACT VENTRICULAR SEPTUM
Pulmonary atresia with the intact ventricular septum (IVS) is a severe cyanotic CHD typified by complete
obstruction of the pulmonary valve, two distinct ventricles, a patent tricuspid valve, and no ventricular
defect [4,22,47-50] . It is an uncommon disorder, present in 1% of all CHDs. The RV is typically hypoplastic with
varying RV sizes. The main PA, as well as PA branches are frequently normal in diameter; this is in contrast
to VSD with pulmonary atresia, in which the PAs are generally smallish with hypoplasia. A PFO is seen in
almost all patients, allowing right to left shunt, helping to decompress the RA. Arteriovenous fistulae of the
coronary arteries may be found in 10% to 50% of infants. A few of these cases may have coronary circulation
dependent on high RV pressure; these babies do not tolerate relieving of obstructive components of the RV.

The blood return from the systemic veins to the RA requires satisfactory egress. Because of an IVS, the only
exit for the RA blood is across an atrial defect. An adequately sized PFO or ASD is critical for RA
decompression. The desaturated blood from the RA traverses through the PFO/ASD into the LA and
combines with the fully oxygenated blood from the pulmonary veins, producing central cyanosis. The PDA