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Congenital heart diseases
encompass a broad spectrum of malformations ranging from mild lesions
that produce minimal symptoms until adult life to severe anomalies
that cause death in the perinatal period.
The cause of most cases of
congenital heart disease is unknown. Genetic and environmental factors
(eg. congenital rubella infection) are responsible for some cases.
Some common
defects like foramen ovale and bicuspid aortic valve are not clinically
significant.
[Foramen
ovale is situated in the inter-atrial wall & is covered by a
moving flap of tissue on the left atrial side. In
intrauterine life, foramen
ovale allows blood flow from right to left atrium, during systole
(high right atrial pressure from collapsed lung).During diastole,
foramen is closed by the flap of tissue due to high left atrial
pressure. After birth,
Foramen is permanently closed within 1-2 days after birth. (low right
atrial pressure due to airy lung & high left atrial pressure) ]
Incidence:
Figures of incidence derived from
several sources are as follows:
Ventricular
septal defect (30-33 %)
Atrial septal
defect (5-8 %)
Patent ductus
arteriosus (8-10 %)
Tetralogy of
Fallot( 8-9 %)
Pulmonary
stenosis (8-10 %)
Aortic stenosis
or atresia (6-8 %)
Coarctation of
aorta (5-6 %)
Transposition of
great arteries (5-10 %)
Total anomalous
pulmonary venous connection (1-2 %)
Truncus
arteriosus (1-2 %)
Ventricular Septal Defect:
Image
This is an
abnormal opening in the ventricular septum that allows free
communication between left and right ventricles. This is the most
common congenital cardiac anomaly.
Image1
;
Image2 .
This is often
associated with Tetralogy of Fallot.
Mostly (90 %) involves the membranous
septum near the aortic valve.
Interventricular septa
develop from above downwards hence, in most of the cases, septal
defects are seen in the basal region, which closes last.
These patients
are at increased risk of infective hepatitis.
Atrial Septal Defect:
Image
This is an
abnormal opening in the atrial septum that allows free communication
of blood. This is the most common congenital cardiac anomaly presenting
in adults and are three types:
i) Primum type:
It is common in Down syndrome. It occurs low in the atrial septum and
occasionally occurs in association with mitral valve deformities.
ii) Secundum
type: This is the commonest type (90 %) and occurs at the foramen
ovale.
iii) Sinus
venosus type: It occurs high in the septum near the superior vena cava
entrance.
Patent Ductus Arteriosus:
In intrauterine
life the ductus arteriosus permits blood flow between the aorta
(distal to the left subclavian artery) and the pulmonary artery.
In a
full-term infant, the ductus usually closes within the first day or
two of life. This is due to relatively high oxygen
tension and reduced local prostaglandin-E synthesis causing ductal
muscular contraction. Persistent patency beyond that
point is generally permanent.
Most of the cases (80-90 %) occur as
isolated defects.
There is associated left ventricle
hypertrophy and pulmonary artery dilation.
Clinical presentation: Initially
asymptomatic, in some cases there may be shortness of breath and poor
feeding habits. Premature infants and those with respiratory distress
syndrome are at increased risk.
In long-standing case it induces
pulmonary hypertension with subsequent right ventricular hypertrophy
and finally right-to-left shunt producing cyanosis.
PDA is also associated with coarctation of the
aorta, transposition of the great vessels, and ventricular septal
defect.
All the above
three conditions i.e.
Ventricular septal defect, atrial septal defect
and patent ductus arteriosus, produce abnormal blood-flow from the
right to left side of heart.
From the outset there is cyanosis as the
poorly oxygenated blood passes into the systemic circulation.
They
also permit emboli from venous sources to pass directly into the
systemic circulation (paradoxic embolism).
Tetralogy of Fallot:
Image
Tetralogy of
Fallot is due to embryologic antero-superior displacement of the
infundibular septum.
Image
Its four cardinal features are :
i) Ventricular
septal defect
ii) Dextroposed
aorta overriding the ventricular septal defect.
iii) Pulmonary
stenosis with right ventricular outflow obstruction.
iv) Right
ventricular hypertrophy.
Additional
cardiac anomalies may be present. Cyanosis is present from birth or
soon after.
Severity of
symptoms is directly related to the extent of right ventricle outflow
obstruction.
With a large
ventricular septal defect and mild pulmonary valvular stenosis, there
is a mild left-to-right shunt without cyanosis. More severe pulmonary
stenosis produces a cyanotic right-to-left shunt.
With complete
pulmonary obstruction, survival is permitted only by flow through a
patent ductus arteriosus or dilated bronchial arterial arteries.
Pulmonary
valvular stenosis protects the lung from volume and pressure
overload, and right ventricle failure is rare owing to decompression
into the left ventricle or aorta.
Transposition of Great Arteries:
Image
The aorta arises
from the right ventricle and the pulmonary artery from the left.
Fetal
development occurs as a result of mixing venous and systemic blood
through the patent ductus arteriosis and a patent foramen ovale.
Therefore, postnatal life critically depends on continued patency of
the ductus as well as ventricular septal defect, atrial septal defect,
or patent foramen ovale.
Prognosis
depends on the severity of tissue hypoxia and the ability of the right
ventricle to maintain aortic flow. If untreated, most children die
within the first few months.
This is
particularly common in children of diabetic mothers, and this
malformation causes cyanosis.
Truncus Arteriosus:
Image
This anomaly is
due to developmental failure of separation of the embryologic truncus
areteriosus into the aorta and pulmonary artery. This results in a
single great artery that receives blood from both ventricles
accompanied by an underlying ventricular septal defect, and that gives
rise to the systemic, pulmonary and coronary circulation.
Patients present
with early cyanosis as a result of right-to-left shunting. Eventually,
the flow reverses, and they develop right ventricle hypertrophy with
pulmonary vascular hypertension. The anomaly carries a poor prognosis.
Coarctation of Aorta:
Image
Coarctation
(narrowing or constriction) of the aorta occurs mainly (50 %) as
isolated defects, the remainder with multiple other anomalies. In most
cases, cardiomagaly (chronic pressure overload hypertrophy) occurs.
Image
Clinical
manifestations depend on the location and severity of the
constriction. Most occur just distal to
the ductus or ligamentum arteriosus (postductal).
Preductal
coarctation:
Manifests
early in life and may be rapidly fatal. Survival depends on the
ability of the ductus arteriosus to sustain blood flow to the distal
aorta and lower body adequately.
Even then, there tends to be lower
body cyanosis, where as the head and arms are unaffected because their
blood supply derives from vessels having origins proximal to the ductus.
This form usually involves a 1 to 5 cm segment of aortic root and is
often associated with fetal right ventricle hypertrophy and early
right-sided heart failure.
Postductal
coarctation:
It is generally
asymptomatic unless severe.
It usually leads to upper extremity
hypertension but low flow and hypotension in the lower extremities,
causing arterial insufficiency (claudication, cold sensitivity).
Collateral flow around the coarctation generally develops with
intercostals rib-notching (noted in x-ray) and internal mammary and
axillary artery dilation.
Even without
treatment, mean life span is 40 years.
Death is due to
congestive
heart failure, aortic dissection proximal to the coarctation,
intracranial hemorrhage or infective endocarditis at the site of
narrowing.
Pulmonary
Valve Stenosis or
Atresia with Intact Interventricular Septum:
Image
This
malformation is the obstruction (stenosis or atresia) at the
pulmonary valve with intact interventricular septum. It may occur in
isolation or with other anomalies.
With complete
pulmonary atresia, there is virtually always a hypoplastic right
ventricle and an atrial septal defect with blood entering the lungs
via a patent ductus arteriosus.
Pulmonary
stenosis generally caused by the fusion of the cusps and may vary from
mild to severe.
Pulmonary
outflow obstruction may also be subvalvular or supravalvular or even
multiple.
Mild stenosis is
generally asymptomatic. Progressively more severe stenoses cause
increasing cyanosis with earlier onset.
Aortic Valve Stenosis and Atresia:
Image
Congenital
complete aortic atresia is rare and incompatible with neonatal
survival.
Survival with
congenital aortic valve stenosis (two types- valvular and subvalvular)
depends on the severity of lesion. Rarely, single-cusp aortic valves
are also seen.
The fate of this
anomaly includes infective endocarditis, left ventricle hypertrophy
(pressure overload), post-stenotic dilation of the aortic root and
rarely sudden death.
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