Congenital heart disease (CHD) refers to structural heart defects present at birth. Diagnosis involves history, physical exam, chest X-ray, ECG, and echocardiogram. Most CHDs can be corrected with surgery if done in a timely manner. Echocardiography can identify and determine severity of specific lesions. Pediatricians must also identify any associated conditions that could impact outcomes.

1. G.ERIC MD4

2. Congenital heart disease (CHD) encompasses a broad and
diverse range of conditions that manifest from prenatal
period to late adulthood. In common usage, CHD refers
to structural heart defects that are present at birthHistory,
physical examination, chest X-ray, ECG and echocardiography
help in identifying the presence of CHD, except
perhaps in the early newborn period where the diagnosis
can be challenging. Palliative or corrective surgery is
feasible for most patients with CHD, provided if undertaken
in a timely fashion. It is also possible to identify
and determine the severity of specific lesions through
echocardiography. systems, or
specific chromosomal and single gene disorders. Pediatricians
need to identify associated conditions, since they
might have significant bearing on outcomes.

3.  Prenatal exposure that increase risk of congenital
 heart disease
 Gestational diabetes (transposition,
atrioventricular septal
 defects, hypoplastic left heart, cardiomyopathy,
PDA)
 Febrile illness in first trimester (increased risk)
 Rubella (PDA, peripheral pulmonary stenosis,
VSD)
 Lupus (complete heart block)
 Phenylketonuria (VSD, TOF, PDA, single ventricle)
 Vitamin deficiency (increased risk of heart
disease)
 Teratogens, (first trimester) e.g. anticonvulsants,

4. The heart assumes its normal four-chambered shape by
the end of six weeks of intrauterine life. From then on only
minor changes occur and consist mainly in the growth of
the heart as a whole with increasing age of the fetus. For
the exchange of gases the fetus is dependent on placental
circulation, whereas the neonate is dependent on the
lungs. Immediately following birth, with the first inspiration,
the lungs expand with air and the gas exchange
function is transferred from the placenta to the lungs. This
necessitates circulatory adjustments following birth to
transform the fetal circulation to the postnatal circulation.

5. Blood oxygenated in the placenta is returned by way of
umbilical veins, which enter the fetus at the umbilicus and
join the portal vein. The ductus venosus
provides a low resistance bypass between the portal vein
and the inferior vena cava. Most of the umbilical venous
blood shunts through the ductus venosus to the
inferiorvena cava. vena cava. On reaching the right
atrium the blood stream is divided into two by the inferior
margin of septum secundum-the crista dividens. About
one-third of the inferior vena cava blood enters the left
atrium, through the foramen ovale, the rest two-thirds
mixes with the venous return from the superior vena cava
to enter the right ventricle.

6. The blood reaching the left atrium from the right atrium
mixes with small amount of blood reaching the left
atrium
through the pulmonary veins and passes to the left
ventricle. The left ventricle pumps out the blood into the
ascending aorta for distribution to the coronaries, head
and upper extremities. The superior vena cava stream,
comprising blood returning from the head and arms,
passes almost directly to the right ventricle. Only minor
quantities (1 to 3%) reaches the left atrium. The right
ventricle pumps out blood into the pulmonary trunk. A
small amount of this blood enters the pulmonary
circulation, the rest passes through the ductus arteriosus
into the descending aorta to mix with the small amount
of blood reaching the descending aorta from the aortic
arch (derived from the left ventricle).

7. The main differences between the fetal and postnatal
circulation are: (i) presence of placental circulation, which
provides gas exchange for the fetus; (ii) absence of gas
exchange in the collapsed lungs; this results in very little
flow of blood to the lungs and thus little pulmonary venous
return to left atrium; (iii) presence of ductus venosus, joining
the portal vein with the inferior vena cava, providing a low
resistance bypass for umbilical venous blood to reach the
inferior vena cava; (iv) widely open foramen ovale to enable
oxygenated blood (through umbilical veins) to reach the left
atrium and ventricle for distribution to the coronaries and
the brain; and lastly ( v) wide open d uctus arteriosus to
allow
right ventricular blood to reach the descending aorta, since
lungs are non-functioning.

9. Circulatory adjustments continue to occur for a variable
period following birth. This change is brought about
because of a shift from placental dependence for gasexchange in
the fetus to pulmonary gas exchange in the
neonate. Loss of placental circulation and clamping of the
umbilical cord, after birth, results in a sudden increase in
systemic vascular resistance with the exclusion of the low
resistance placental circulation. This tends to increase the
aortic blood pressure and the left ventricular systolic
pressure. The left ventricular diastolic pressure also tends to
rise and increases the left atrial pressure. The loss of placental
circulation results in a sudden reduction of flow through
the ductus venosus that closes off. Flow through the ductus
venosus disappears by the 7th day of postnatal life. The loss
of placental flow results in a decrease in the volume of blood
returning to the right atrium.

10. The right atrial pressure
decreases. The left atrial pressure becomes higher than the
right atrial pressure and the septum primum, which acts as
a valve of the fossa ovalis, approximates with the septum
secundum to close off the foramen ovale. Functional closure
of the foramen ovale occurs relatively quickly. Over a period
of months to years, the septum primum and septum
secundum become firmly adherent resulting in anatomical
closure of the foramen ovale. Sudden expansion of lungs with the first few
breaths
causes a fall in pulmonary vascular resistance and an
increased flow into the pulmonary trunk and arteries. The
pulmonary artery pressure falls due to lowering of
pulmonary vascular resistance. The pressure relations
between the aorta and pulmonary trunk are reversed so
that the flow through the ductus is reversed. Instead of
blood flowing from the pulmonary artery to aorta, the
direction of flow through the ductus, is from the aorta to
pulmonary trunk

11. The increased saturation following birth
causes the ductus arteriosus to constrict and close.
Somefunctional patency and flow can be demonstrated
through
the ductus arteriosus for a few days after birth. The ductus
arteriosus closes anatomically within 10 to 21 days.
This results in the establishment of the postnatal
circulation. Over the next several weeks, the pulmonary
vascular resistance continues to decline. There is fall in
the pulmonary artery and right ventricular pressures. The
adult relationship of pressures and resistances in the
pulmonary and systemic circulations is established by the
end of approximately two to three weeks

12. CHD has been broadly classified as cyanotic and acyanotic
heart disease. While broad classifications
work for most situations, there are patients who cannot
be classified into common physiologic categories.
Additionally there are often specific issues such as valve
regurgitation that determine the clinical manifestations.
The following physiological concepts are important to
understand common congenital malformations:
i. Pre-tricuspid versus post-tricuspid shunts
ii. The VSD-PS physiology
iii. Single ventricle physiology
iv. Duct dependent lesions
vi. Unfavorable streaming and parallel circulation

13. Pre-tricuspid versus post-tricuspid shunts Acyanotic
heart disease with left to right shunts is traditionally
classified as pre-tricuspid and post-tricuspid shunts. There
are important differences in physiology that impact clinical
manifestations and natural history. Left to right shunts ator
proximal to the level of the atria are known as pretricuspid
shunts. They include atrial septal defects and
partial anomalous pulmonary venous connection. The left
to right shunt and the consequent excessive pulmonary
blood flow is dictated by relative stiffness of the two
ventricles. Since the right ventricle is relatively stiff
(noncompliant)
at birth and during early infancy the shunt is
small.

14. Over the years the right ventricle progressively
enlarges to accommodate the excessive pulmonary
blood
flow. The pulmonary vasculature also becomes
capacious
to gradually accommodate the excessive blood flow.
This
explains why atrialseptal defects (ASD) seldom manifest
with symptoms of pulmonary over-circulation during
infancy and childhood. The clinical signs are also easily
explained by the physiology of pre-tricuspid shunts.
Thediastolic flow murmur of ASD is across the much
larger
tricuspid valve and is therefore relatively subtle or even
inaudible.

15. The excessive blood in the right ventricle is
ejected into the pulmonary artery resulting in an ejection
systolic murmur. The second heart sound splits widely
and is fixed because of the prolonged right ventricular
ejection time and prolonged "hang-out" interval resulting
from increased capacitance of the pulmonary circulation.
Pulmonary arterial hypertension (P AH) is typically absent
or, at most, mild. The presence of moderate or severe P AH
in ASD is uncommon but worrisome and may suggest
the onset of irreversible changes in the pulmonary
vasculature. Post-tricuspid shunts are different in that there is
direct
transmission of pressure from the systemic to the
pulmonary circuit at the ventricular level (VSD) or great
arteries (PDA and aorto-pulmonary window). The
shunted blood passes through the lungs and finally leads
to a diastolic volume overload of the left ventricle.

16. The
hemodynamic consequences are dictated by the size of
the defect. For patients with large post-tricuspid shunts,
symptoms begin in early infancy, typically after some
regression of elevated pulmonary vascular resistance in
the newborn period together with progressive
development of the pulmonary vascular tree. The excessive
pulmonary blood flow returns to left
atrium and flows through the mitral valve resulting in
apical diastolic flow murmur that is a consistent marker
of large post-tricuspid shunts. The left atrium and ventricle
are dilated as a result of this extra volume. Elevated
pulmonary artery pressure is an inevitable consequence
of large post-tricuspid shunts, and is labeled hyperkinetic
P AH. This needs to be distinguished from elevated
pulmonary vascular resistance that results from longstanding
exposure to increased pulmonary blood flow.

17. This situation
is characterized by a large communication at the
ventricular
level together with varying degrees of obstruction
to pulmonary blood flow. Typically, this is in the form of
subvalvar (infundibular), valvar, annular (small annulus)
and occasionally supra-valvar stenosis. The free
communication
between the two ventricles results in equalization
of pressures. Severity of PS dictates the volume of blood
flowing through pulmonary arteries and therefore
amount
of oxygenated blood returning via pulmonary veins.
Severe PS results in right to left shunt across the VSD
with
varying degrees of hypoxia and, consequently, cyanosis.

18. Cyanosis is directly proportionate to the severity of PS.
Because the right ventricle is readily decompressed by the
large VSD, heart failure is unusual. The best example of
VSD-PS physiology is tetralogy of Fallot (TOF). In its least
severe form, TOF is often not associated with cyanosis
(pink TOF). Here PS is significant enough to result in a
large pressure gradient across the right ventricular
outflow tract (RVOT), but not severe enough to result in areduction in
pulmonary blood flow. Pink TOF is typically
associated with a loud ejection systolic murmur because
of a reasonable volume of blood flowing across the RVOT.
As the severity of PS increases, pulmonary blood flow
declines and the intensity of murmur declines
progressively. Identical symptoms and physical findings
are present in (i) complete transposition of great arteries
with VSD and pulmonic stenosis, (ii) double outlet right
ventricle with pulmonic stenosis and a large subaortic
VSD, (iii) tricuspid atresia with diminished pulmonary
blood flow, (iv) single ventricle with pulmonic stenosis,
and (v) corrected transposition of great arteries with VSD
and pulmonic stenosis.

19. This refers to a group of
conditions where there is complete mixing of pulmonary
and systemic venous returns. In addition to single ventricle
( double inlet ventricle), a variety of conditions come under
the category of single ventricular physiology. Atresia of one
of the AV valves, severe hypoplasia of one of the ventricles,
severe straddling of one of the AV valves over a large VSD
are all examples of situations where there is mixing of
pulmonary and systemic venous returns. The clinical
manifestations are dictated by the whether or not there is
PS. In absence of PS, there is excessive pulmonary flow
especially in infants because of the relatively lower
pulmonary vascular resistance. The proportion of
oxygenated blood from pulmonary veins that mixes with
the systemic venous return is high. Cyanosis is minimal and
measured oxygen saturation may be in the 90s. However,
the price for preserved oxygenation is heart failure and
permanent elevation of pulmonary vascular resistance
(pulmonary vascular obstructive disease or PVOD). If the
child survives infancy, pulmonary vascular resistance
progressively increases with increasing cyanosis.

20. Single ventricle and its physiologic variants can be
associated with varying degrees of PS. The features are
similar to VSD-PS physiology except for relatively
severe
hypoxia because of free mixing of systemic and
pulmonary
venous return.
Palliative operations are the only option for the large
number of conditions that come under the category of
single ventricle physiology. Single ventricle palliation is
done in stages. The final procedure is the Fontan
operation
that allows separation of systemic venous return from
pulmonary venous return thereby, eliminating cyanosis.

21. An infant or a newborn with
CHD that is dependent on the patency of the ductusarteriosus
for survival can be termed as having a duct
dependent lesion. These are newborns where the systemic
blood supply is critically dependent on an open PDA (duct
dependent systemic circulation, DDSC) or pulmonary
blood flow is duct dependent (duct dependent pulmonary
circulation, DDPC). Closure of the PDA in DDSC results
in systemic hypoperfusion (often mistaken as neonatal
sepsis), as in hypoplastic left heart syndrome where theentire systemic
circulation is supported by the right
ventricle through the PDA and interrupted aortic arch
where the descending aortic flow is entirely through the
PDA. Neonates with duct dependent physiology require
prostaglandin El (PGEl) for survival. Early recognition
of a duct dependent situation allows early initiation of
PGEl and stabilization until definitive procedure is
accomplished.

22. Recognition and Diagnostic Approach
While it is often easy to recognize the presence of CHD
in
older children, manifestations of heart disease can
often
be subtle in newborns and young infants. Conditions
that
do not primarily involve the cardiovascular system can
result in clinical manifestations that overlap with those
resulting from CHD in the newborn. Nonetheless,
careful
clinical evaluation is often rewarding and allows
identification of CHD in most infants and many
newborns.
The following clinical features should alert the
paediatrician regarding the presence of CHD.

23. Cyanosis. Parents seldom reportcyanosis unless itis relatively
severe (saturation <80%). It is often easier for them to notice
episodic cyanosis (when the child cries or exerts).
Difficult feeding and poor growth. The parent of an infant
with CHD may complain that the child has difficulty with
feeds. This is usually a feature of an infant with congestive
heart failure resulting from CHD. The history may be of
slow feeding, small volumes consumed duritiring easily following
feeds and requirement of periods
of rest during feeds. Excessive sweating involving
forehead or occiput is commonly associated. Not
infrequently, no history of feeding difficulty may be
obtained, but examination of the growth charts will reveal
that the child's growth rate is not appropriate for age. A
recent decline in growth rate (falling off the growth curve)
or weight that is inappropriate for age (<5th centile) may
result from a large left to right shunt. Characteristically,
growth retardation affects weight more that heightng each feed,

24. Difficult breathing. Tachypnea (respiratory rates more than
60/min in infants <2 months; >50/min in older infants;
>40/min after 1 yr) is a characteristic manifestation of
heart failure in newborns. For infants, subcostal or
intercostal retractions together with flaring of nostrils are
frequently associated with tachypnea.
Frequent respiratory infections. The association of respiratory
infections that are frequent, severe and difficult to treat
with large left to right shunts is not a specific feature.
Specific syndromes. The presence of chromosomal anomalies
or other syndromes that are associated with CHD should
alert the clinician to the presence of specific cardiac defects.
Trisomy 21 is the commonest anomaly associated with
heart disease; others include trisomy 13 and 18, Turner
and Noonan syndromes, and velocardiofacial and Di
George syndromes (

25. Nadas' Criteria
The assessment for presence of heart disease
can be done
using the Nadas' criteria. Presence of one
major or two
minor criteria are essential for indicating the
presence of
heart disease. It is important to recognize
that these criteria are of limited use in
newborns, where
clinical signs are subtle.

26. Major criteria
(i) Systolic murmur grade III or more in intensity. A pansystolic
murmur is always abnormal no matter what is its intensity.
There are only three lesions that produce a pansystolic
murmur, and these are (a) VSD, (b) mitral regurgitation
and (c) tricuspid regurgitation. An ejection systolic murmur
may be due to an organic cause or it may be functional. An
ejection systolic murmur associated with a thrill is an
organic murmur. Grade III ejection systolic murmur of a functional type may
be heard in anemia or high fever
especially in small children.
A number of children around the age of 5 yr may have a soft
ejection systolic murmur. If it is accompanied with a normal
second sound then it is unlikely to be significant. Before
discarding a murmur as of no significance, it is necessary
to obtain an electrocardiogram, and a thoracic
roentgenogram. If they are also normal, one can exclude
heart disease, but at least one more evaluation after six
months is essential.

27. (ii) Diastolic murmur. The presence of a diastolic murmur
almost always indicates the presence of organic heart
disease.
(iii) Central cyanosis. Central cyanosis suggests that either
unoxygenated blood is entering the systemic circulation
through a right to left shunt or the blood passing through
the
lungs is not getting fully oxygenated. The oxygen saturation
of the arterial blood is less than normal, the normal being
around 98%. If the blood is not getting fully oxygenated
in the lungs, it is called pulmonary venous desaturation and
indicates severe lung disease. Cyanosis due to a right to
left cardiac shunt indicates presence of heart disease.
Central cyanosis is present in fingers and toes as well as
in the mucous membranes of mouth and tongue. It results
in polycythemia and clubbing.

28. Peripheral cyanosis does not imply the presence of heart
disease. Peripheral cyanosis is the result of increased oxygen
extraction from the blood by the tissues. It is seen in fingers
and toes but not in mucous membrane of mouth and
tongue. The arterial oxygen saturation is normal. Presence
of central cyanosis always indicates presence of CHD if
lung disease has been excluded. However, cyanosis that
is obvious clinically usually results from significant
desaturation (typically <85%). Poor lighting, anemia, dark
skin complexion may further mask hypoxia. Routine use
of the pulse oximeter allows detection of milder forms of
hypoxia. Saturations of 95% or lower while breathing
room air are abnormal.
(iv) Congestive cardiac failure. Presence of congestive cardiac
failure indicates heart disease except in neonates and
infants, who might show cardiac failure due to extracardiac
causes, including anemia and hypoglycemia.

29. Minor criteria
(i) Systolic murmur less tlzan grade III. It is emphasized that
soft, less than grade three murmurs by themselves do not
exclude heart disease.
(ii) Abnormal second sound. Abnormalities of the second
sound always indicate presence of heart disease. It has
been included as a minor criterion only because
auscultation is an individual and subjective finding.
(iii) Abnonnal electrocardiogram. Electrocardiogram is used
to determine the mean QRS axis, right or left atrial
hypertrophy and right or left ventricular hypertrophyCriteria
for ventricular hypertrophy, based only on voltage
criteria are not diagnostic for the presence of heart disease.
The voltage of the QRS complexes can be affected by
changes in blood viscosity, electrolyte imbalance, position
of the electrode on the chest wall and thickness of the chest
wall.

30. (iv) Abnormal X-ray. The reason for considering
abnormal
X-ray as a minor criterion is twofold. In infants and
smaller
children, the heart size varies considerably in expiration
and inspiration. If there is cardiomegaly on a good
inspiratory film, it suggests presence of heart disease.
The
second reason is the presence of thymus in children up
to
the age of two years, which might mimic cardiomegaly.
Fluoroscopy is helpful in separating the shadow of the
thymus from the heart.
(v) Abnormal blood pressure. It is difficult to obtain
accurate
blood pressure in smaller children. It is important to use
appropriate sized cuffs while measuring blood pressure.

31.  Nadas' criteria for
clinical diagnosis of
congenital
 heart disease
 Major
 Systolic murmur
grade III
 or more
 Diastolic murmur
 Cyanosis
 Congestive cardiac
failure
 Minor
 Systolic murmur
grade I or II
 Abnormal second
sound
 Abnormal
electrocardiogram
 Abnormal X-ray
 Abnormal blood
pressure

32. Imaging Studies
Echocardiography Echocardiography has
revolutionised the diagnosis of CHO and its
high
diagnostic yield makes this investigation cost
effective.
This is particularly true for infants and
newborns in whom
excellent images are readily obtained.
Transesophageal
echocardiography can supplement
transthoracic studies

33. Cardiac magnetic resonance imaging Cardiac
magnetic resonance imaging is an important
modality for
evaluation of CHO, especially in older patients and
for
postoperative evaluation. Magnetic resonance
imaging
can also define extracardiac structures such as
branch
pulmonary arteries, pulmonary veins and
aortopulmonary
collaterals. Very useful physiologic data (especially
blood

34. A number of complications occur in patients with CHD.
Pulmonary arterial hypertension (PAH) Lesions that
have the greatest likelihood of developing PAH include
cyanotic heart disease with increased pulmonary blood
flow. Here irreversible changes in pulmonary
vasculature
develops rapidly often during infancy. It is particularly
important to correct or appropriately palliate these
lesions
early (ideally within the first few months of life). Large
acyanotic post-tricuspid shunts are also prone to
early
development of PAH and should be ideally corrected
early, preferably within the first year. In pre-tricuspid
shunts, P AH develops slowly and unpredictably.

35.  Broad physiologic categories of congenital
heart
 disease
 Acyanotic heart disease: Left to right
shunts
 Pre-tricuspid: Partial anomalous pulmonary
venous drainage,
 atrial septa! defect
 Ventricular: Ventricular septa! defects (VSD)
 Great artery: Aorto-pulmonary window,
patent ductus;
 ruptured sinus of Valsalva
 Both pre- and post-tricuspid:
Atrioventricular septa! defect,
 left ventricle to right atrial communications
 Acyanotic heart disease: Obstructive
lesions
 Inflow: Cor-triatriatum, obstructive lesions
of the mitral valve
 Right ventricle: Infundibular stenosis,
pulmonary valve
 stenosis, branch pulmonary artery stenosis
 Left ventricle: Subaortic membrane, valvar
aortic stenosis,
 supravalvar aortic stenosis, coarctation of
aorta
 Miscellaneous: Coronary artery
abnormalities, congenital
 mitral and tricuspid valve regurgitation
 Cyanotic heart disease
 Reduced pulmonary blood flow
 Intact interventricular septum: Pulmonary
atresia with intact
 ventricular septum, critical pulmonic
stenosis with right to
 left shunt at atrial level, Ebstein anomaly;
isolated right
 ventricular hypoplasia
 Unrestrictive ventricular communication:
All conditions listed
 under VSD with pulmonic stenosis
 Increased pulmonary blood flow
 Pre-tricuspid: Total anomalous pulmonary
venous
 communication, common atrium
 Post-tricuspid: All single ventricle
physiology lesions without
 pulmonic stenosis, persistent truncus
arteriosus, transposition
 of great vessels
 Pulmonary hypertension
 Pulmonary vascular obstructive disease
(Eisenmenger
 physiology)
 Miscellaneous
 Pulmonary arteriovenous malformation,
anomalous drainage
 of systemic veins to LA

36. While
most patients with ASD will have mild or no PAH
throughout their lives, a small proportion develop
accelerated
changes in the pulmonary vasculature. Some of
the key features associated with the development of
PAH
include: large size of the defect; presence of pulmonary
venous hypertension; airway obstruction or syndromic
association, (e.g. trisomy 21); prolonged duration of
exposure
to increased pulmonary blood flow; and residence at
high altitude.

37. Infective endocarditis or endarteritis (IE) Endocarditis
can complicate CHD, especially in patients with significant
turbulence created by high-pressure gradients, e.g.
restrictive
VSD and PDA, tetralogy of Fallot, and left ventricular
outflow tract obstruction. Some surgical operations (such as
the Blalock-Taussig shunt) are also associated with
increased
risk of IE or endarteritis. Lesions with little or no turbulent
flows, such as ASD are not associated with increased risk.
The risk of endocarditis increases after dentition, hence the
importance of good dental hygiene in patients with CHD
cannot be over emphasized.

38. Growth and nutrition This is affected in all
forms of CHD
and is particularly striking in large left to right
shunts.
Children with CHD show high prevalence of
malnutrition,
which improves after correction of the
underlying
condition. Catch up growth is slow if CHD is
corrected late.

39. Myocardial dysfunction Chronic volume overload
results in ventricular enlargement and ventricular
dysfunction that is typically reversed after correction. A
small proportion of patients with severe hypoxia also
develop severe dysfunction involving both ventricles.
Heart failure is mostly the result of hemodynamic
consequences of increased pulmonary blood flow,
mitral
or tricuspid valve regurgitation and severe myocardial
hypertrophy. Systolic dysfunction is a relatively less
common cause.

40. Neurologic and neurodevelopmental consequences
Chronic hypoxia, in utero hypoxia and hypoperfusion
and open-heart surgery contribute substantially
to morbidity. Brain abscess is uniquely associated with
cyanotic heart disease (typically beyond the age of 2 yr)
where the right to left shunt bypasses the pulmonary
filter.
Polycythemia Older children with cyanotic CHD are
prone to complications from a chronically elevated red
cell turnover. These include symptoms of
hyperviscosity,
gout, renal failure and gall stones.

41. Rhythm disorders and sudden death Chronic
enlargement
of heart chambers predispose to tachyarrhythmia.
Chronic right atrial enlargement (such as atrial septal
defect,
Ebstein syndrome, severe tricuspid regurgitation)
predisposes to atrial flutter, which might be
persistent and
refractory. Chronic right ventricular enlargement
predisposes
to ventricular tachycardia and may precipitate
sudden cardiac arrest. This is a significant longterm
concern
after TOP repair where the pulmonary valve is rendered
incompetent. Similarly left ventricular hypertrophy and
dysfunction are associated with high risk of ventricular
tachycardia.

42. Cyanotic spells Patients with the VSD-PS physiology are
prone to cyanotic spells. Cyanotic spells are due to an
acute
decrease in pulmonary blood flow, increased right to
left
shunt and systemic desaturation due to (i) Infundibular
spasm due to increase in circulating catecholamines,
during feeding or crying; (ii) Activation of
mechanoreceptors
in right ventricle (due to decrease in systemic
venous return) or in left ventricle (due to decrease in
pulmonary blood flow), leads to peripheral
vasodilatation
and fall in systemic vascular resistance producing
increased right to left shunt and systemic desaturation.

43. Natural History
Some defects have a tendency towards spontaneous
closure and this can influence the timing of
intervention.
The defects known to close spontaneously are atrial
and
ventricular septal defects, and patent ductus arteriosus.
The variables influencing the likelihood of spontaneous
closure include: age at evaluation (lower likelihood of
closure with increasing age), size of the defect (smaller
defects more likely to close) and location of the defects
(fossa ovalis ASD and perimembranous and muscular
VSDs can close on their own)

44. A review of natural history of common forms of CHD
shows that without correction, many children with CHD
(especially those with cyanotic CHD) will not survive
beyond early childhood. The outcomes are improved by
correction through surgery and, in some situations,
through catheter interventions. Despite curative surgery,
some patients have important longterm sequelae. For
example, patients with tetralogy of Fallot who have
undergone curative repair might show progressive right
ventricular dilation with increased risk of late heart failure
and sudden cardiac death. There are longterm concerns
after the arterial switch operation (aortic root dilation,
silent coronary occlusion), AV canal repair (AV valve
regurgitation) and coarctation (residual hypertension,
aortic aneurysm).

45. Operations that involve placement of
conduits (pulmonary atresia, Rastelli operations)
require
replacement upon growth of the child. Conditions
associated with satisfactory longterm survival include
small left to right shunts and bicuspid aortic valves.
survival is also satisfactory for many patients with atrial
septal defect, coarctation of aorta, pink TOF, mild
Ebstein
anomaly and some forms of corrected transposition of
great arteries.