Cardiac Path Online
Pathology of Congenital Heart Disease
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 (Example: 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) ]
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 %)
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.
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:
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:
Tetralogy of Fallot is due to embryologic antero-superior displacement of the infundibular septum.
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:
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.
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 (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.
Clinical manifestations depend on the location and severity of the constriction.
Most occur just distal to the ductus or ligamentum arteriosus (postductal).
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.
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:
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:
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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