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Page 16 of 43 Rao. Vessel Plus 2022;6:26 https://dx.doi.org/10.20517/2574-1209.2021.93

drain into multiple sites. Most frequently, the common pulmonary vein drains into the left innominate vein.
Other connection sites are: superior vena cava, coronary sinus, portal vein, or other unusual places [4,22-24] .
The TAPVC is the fifth most frequent cyanotic CHD accounting for 2% to 3% of all CHDs. Two
classifications of TAPVC exist, the first is based on the site to which the connecting anomalous vein
drains [25,26] and the second is based on physiology, i.e., obstructive and non-obstructive [26,27] . As per the first
classification, they are supra-cardiac in 45%, cardiac in 25%, infra-cardiac in 25%, and mixed in 5% cases.
Connection of the CPV to the left innominate vein is the utmost common type among all cases of TAPVC
while the drainage into a structure below the level of diaphragm (infra-diaphragmatic) is the most common
variety in a symptomatic newborn. The classification based on physiology (obstructive and non-obstructive)
is helpful in clinical recognition and management. Supra-diaphragmatic TAPVC is usually non-obstructive,
[27]
although obstruction lesions have been reported in this group also, as discussed elsewhere . On the other
hand, obstruction is universal in infra-diaphragmatic TAPVC patients.

The entirety of the pulmonary venous return ultimately drains into the RA in all types of TAPVC. Hence,
the admixture of the pulmonary and systemic venous returns (plus the blood return from the coronary
sinus) occurs in the RA. Consequently, shunting from the RA to LA through the PFO (or ASD) is necessary
to provide systemic flow. The relative flow distribution to systemic (via the PFO) and pulmonary (via the
tricuspid valve) circulations is reliant on the respective compliances of the RV and LV.

Echo-Doppler examination is helpful in establishing the diagnosis of TAPVC and assessing central issues
relevant in the treatment of these infants [22,24] . In normal babies, the connection of the pulmonary veins to
the LA is easily shown in the suprasternal notch crab-view [Figure 28]. Other views also can demonstrate
the entrance of the pulmonary venous structures into the LA. If the entrance of pulmonary veins into the
LA by color Doppler cannot be demonstrated, the possibility of TAPVC should be considered. Also, when
there is marked elevation of the RV/PA pressures [Figure 29A] and/or a pure right to left shunt through the
PFO [Figure 29B], a diagnosis of TAPVC should be suspected. However, it should be noted that these
findings can also be present in babies with persistent pulmonary hypertension and at times in babies with
severe aortic coarctation.

The right heart structures (RA, RV, and PA) are dilated in all varieties of TAPVC [Figure 30] while the LA
and LV generally look smaller than the right heart structures. A smaller LA than normal may in part be
related to no contribution of the CPV to the LA size; however, it is easily visualized [Figure 30A, B and D].
The LV appears to be compressed posteriorly [Figure 30A and C] and to the left [Figure 30D] by the
enlarged RV.

The RV and PA systolic pressures are increased, particularly in the infra-diaphragmatic types, and can be
shown by a markedly increased tricuspid insufficiency jet velocity [Figure 29A]. A simplified Bernoulli
formula may appraise these pressures:

2
RV and PA systolic pressure = 4V + 5 mmHg
RV, right ventricle; PA, pulmonary artery; V, the peak velocity of tricuspid insufficiency jet; and 5 mmHg is
assumed pressure in the PA.

Shunting from the RA to LA through the PFO is also present in all varieties of total veins [Figure 29B].