Chapter 12: CHD: Right to Left Shunt

Question 1

What are Right to Left shunts?

Answer 1

The diseases in this group cause cyanosis early in postnatal life (cyanotic congenital heart
disease).

Question 2

What is the most common anomaly in the Right to Left shunt?

Answer 2

Tetralogy of Fallot, the most common in this group, and transposition of the great
arteriesare illustrated schematically in Figure 12-6 .

The others include persistent truncus
arteriosus, tricuspid atresia, and total anomalous pulmonary venous connection

Question 3

What are your Right to Left anomalies?

Answer 3

• Tetralogy of Fallot
• transposition of the great arteries
• persistent truncus arteriosus,
• tricuspid atresia, and
• total anomalous pulmonary venous connection

RighT ( you can hear the T rather than the word Left?

Question 4

Answer 4

FIGURE 12-6 Schematic of the most important right-to-left shunts (cyanotic congenital heart
disease).

• A, Classic tetralogy of Fallot. The direction of shunting across the ventricular septal defect (VSD) depends on the degree of the subpulmonary stenosis; when severe, a right-to-left shunt results (arrow).
• B, Transposition of the great arteries with and without VSD. Ao, aorta; LA, left atrium; LV, left ventricle; PT, pulmonary trunk; RA, right atrium; RV, right ventricle.

Question 5

What are the four cardinal features of the TOF?

Answer 5

The four cardinal features of the tetralogy of Fallot (TOF) are

• (1) VSD,
• (2) obstruction of the right ventricular outflow tract (subpulmonary stenosis),
• (3) an aorta that overrides the VSD, and
• (4) right ventricular hypertrophy ( Fig. 12-6A ).

All of the features result embryologically from

anterosuperior displacement of the infundibular septum.

Question 6

All the features of the TOF result from what?

Answer 6

All of the features result embryologically from

anterosuperior displacement of the infundibular septum.

Question 7

What is the hallmark morphology of TOF in xray?

Answer 7

Morphology.

The heart is often enlarged and may be “boot-shaped” as a result of marked
right ventricular hypertrophy, particularly of the apical region.

Question 8

What is the reason why TOF has a “ boot-shaped “ appearance?

Answer 8

Morphology.

The heart is often enlarged and may be “boot-shaped” as a result of marked right ventricular hypertrophy, particularly of the apical region.

Question 9

Desribe TOF VSD features.

Answer 9

The VSD is usually large.

Question 10

Describe the overiding feature of the TOF as one of its features.

Answer 10

The aortic valve forms the superior border of the VSD, thereby overriding the defect and both
ventricular chambers.

Question 11

Desribe why subpulmonic stenosis occurs in TOF.

Answer 11

The obstruction to right ventricular outflow is most often due to narrowing of the infundibulum (subpulmonic stenosis) but can be accompanied by pulmonary
valvular stenosis.

Question 12

What is necessary for survival of patient’s with TOF when there sometimes there is complete atresis?

Answer 12

Sometimes there is complete atresia of the pulmonary valve and variable portions of the pulmonary arteries, such that blood flow through a patent ductus arteriosus, dilated bronchial arteries, or both, is necessary for survival.

Aortic valve insufficiency or an
ASD may also be present; a right aortic arch is present in about 25% of cases.

Question 13

Is it true that even untreated patients with TOF survive into adult life?

T or F

Answer 13

True

Even untreated, some patients with TOF survive into adult life (in reports of untreated patients
with this condition, 10% were alive at 20 years and 3% at 40 years). [49]

Question 14

What are the clinical consequences of TOF?

Answer 14

The clinical consequences depend primarily on the severity of the subpulmonary stenosis, as this
determines the direction of blood flow.

If the subpulmonary stenosis is mild, the abnormality
resembles an isolated VSD, and theshunt may be left-to-right, without cyanosis (so-called pink
tetralogy).

As the obstruction increases in severity, there is commensurately greater resistance
to right ventricular outflow. As right-sided pressures approach orexceed left-sided pressures, right-to-left shunting develops, producing cyanosis (classic TOF).

With increasingly severe
subpulmonic stenosis, the pulmonary arteries become progressively smaller and thinner walled
(hypoplastic), and the aorta grows progressively larger in diameter.

As the child grows and the
heart increases in size, the pulmonic orifice does not expand proportionally, making the
obstruction progressively worse.

Most infants with TOF are cyanotic from birth or soon
thereafter.

The subpulmonary stenosis, however, protects the pulmonary vasculature from pressure overload, and right ventricular failure is rare because the right ventricle is decompressed by the shunting of blood into the left ventricle and aorta.

Complete surgical
repair is possible for classic TOF but is more complicated for persons with pulmonary atresia
and dilated bronchial arteries.

Question 15

When will a TOF resemble an isolated VSD?

Answer 15

If the subpulmonary stenosis is mild, the abnormality
resembles an isolated VSD, and the shunt may be left-to-right, without cyanosis (so-called pink
tetralogy).

Question 16

When does a classic TOF happens?

Answer 16

As the obstruction increases in severity, there is commensurately greater resistance to right ventricular outflow.

As right-sided pressures approach or exceed left-sided pressures, right-to-left shunting develops, producing cyanosis (classic TOF).

With increasingly severe
subpulmonic stenosis, the pulmonary arteries become progressively smaller and thinner walled
(hypoplastic), and the aorta grows progressively larger in diameter.

As the child grows and the
heart increases in size, the pulmonic orifice does not expand proportionally, making the
obstruction progressively worse.

Most infants with TOF are cyanotic from birth or soon
thereafter.

The subpulmonary stenosis, however, protects the pulmonary vasculature from pressure overload, and right ventricular failure is rare because the right ventricle is decompressed by the shunting of blood into the left ventricle and aorta.

Complete surgical
repair is possible for classic TOF but is more complicated for persons with pulmonary atresia
and dilated bronchial arteries.

Question 17

What is TGA?

Answer 17

Transposition of the great arteries (TGA) produces ventriculoarterial discordance: the aorta
arises from the right ventricle, and lies anterior and to the right of the pulmonary artery, which
emanates from the left ventricle ( Fig. 12-7 ; see also Fig. 12-5B ).

The AV connections are
normal (concordant), with the right atrium joining the right ventricle and the left atrium emptying
into the left ventricle.

The embryologic defect in complete TGA stems from abnormal formation of the truncal and aortopulmonary septa.

The result is separation of the systemic and
pulmonary circulations, a condition incompatible with postnatal life unless a shunt exists for
adequate mixing of blood.

Question 18

What is the embryologic defect in complete TGA?

Answer 18

The embryologic defect in complete TGA stems from abnormal formation of the truncal and aortopulmonary septa.

The result is separation of the systemic and
pulmonary circulations, a condition incompatible with postnatal life unless a shunt exists for
adequate mixing of blood.

Question 19

Answer 19

FIGURE 12-7 Transposition of the great arteries

Question 20

What is the outlook for infants with TGA?

Answer 20

The outlook for infants with TGA depends on the degree of “mixing” of the blood, the magnitude
of the tissue hypoxia, and the ability of the right ventricle to maintain the systemic circulation.

Question 21

When do patient’s with TGA may have a stable shunt?

Answer 21

Patients with TGA and a VSD (∼35%) may have a stable shunt.

Question 22

Which patient with TGA have an unstable shunts?

Answer 22

Those with only a patent
foramen ovale or ductus arteriosus (∼65%), however, have unstable shunts that tend to close
and therefore require immediate intervention to create a new shunt (such as balloon atrial
septostomy) within the first few days of life.

Right ventricular hypertrophy becomes prominent,
because this chamber functions as the systemic ventricle.

Concurrently, the left ventricle
becomes thin-walled (atrophic) as it supports the low-resistance pulmonary circulation.

Without
surgery, most patients die during the first few months of life. However, as a result of considerable improvements in surgical repair over the past several decades, many persons with TGA now survive to adulthood

Question 23

What is PTA?

Answer 23

Persistent truncus arteriosus (PTA) arises from a developmental failure of separation of the
embryologic truncus arteriosus into the aorta and pulmonary artery.

This results in a single great artery that receives blood from both ventricles and gives rise to the systemic, pulmonary, and coronary circulations.

.

Question 24

Why does PTA produces systemic cyanosis?

Answer 24

Because there is an associated VSD and mixing of blood from the right and left ventricles, PTA produces systemic cyanosis as well as increased pulmonary blood
flow, with the danger of irreversible pulmonary hypertension

Question 25

What is Tricuspid Atresia?

Answer 25

Complete occlusion of the tricuspid valve orifice is known as tricuspid atresia.

Question 26

Tricuspid Atresia results from what?

Answer 26

It results embryologically from unequal division of the AV canal; thus, the mitral valve is larger than
normal, and there is almost always underdevelopment (hypoplasia) of the right ventricle.

The
circulation is maintained to some degree by a right-to-left shunt through an interatrial communication (ASD or patent foramen ovale) and a VSD, which affords communication between the left ventricle and the pulmonary artery that arises from the hypoplastic right
ventricle.

Cyanosis is present virtually from birth, and there is a high mortality in the first weeks
or months of life.

Question 27

What is Total Anomalous Pulmonary Venous Connection?

Answer 27

Total anomalous pulmonary venous connection (TAPVC), in which the pulmonary veins fail to
directly join the left atrium,results embryologically when the common pulmonary vein fails to
develop or becomes atretic.

Fetal development is made possible by primitive systemic venous channels that usually drain from the lung into the left innominate vein or to the coronary sinus.