Pathology of Congenital Heart Disease


Atrial Septal Defect

 There are many types of atrial septal defects, these are:

  • Secundum atrial septal defect is due to a defect in the foramen ovale membrane
  • Sinoseptal defect is involves the atrial septum between the sinus venosus component of the two atria, this could be:
    1. Sinus venosus atrial septal defect, a defect of the atrial septum adjacent to the superior vena cava entrance into the right atrium. The right upper pulmonary vein typically would drain into the right atrium. It may or may not be aberrant in itís communication to the left atrium
    2. Inferior vena cava sinus venosus atrial septal defect is when the defect is inferior & closer to the right atrium-inferior vena cava junction
    3. Unroofed coronary sinus, this will lead to a communication (and shunting) between the LA and the coronary sinus.

True anomalous pulmonary venous connection with the inferior vena cava type sinus atrial septal defect is seen in scimitar syndrome. Scimitar syndrome is when one or more of the right pulmonary veins drain into the IVC with hypoplasia of right lung with or without pulmonary blood supply of the affected lung tissue from the descending aorta instead of the pulmonary circulation, this may be associated with an atrial septal defect.

Rarely does anomalous pulmonary venous drainage occur with an intact atrial septum.

  • Primum atrial septal defect is when the atrial septum does not attach to the atrio-ventricular valve apparatus leading to an inter-atrial communication just above the atrioventricular valve. This may be associated with atrioventricular valve defect or cleft of the mitral valve.
  • Common atrium m is when the entire atrial septum is missing. Right to left shunting occur with this anomaly leading to cyanosis. This is associated with mitral valve prolapse(MVP).

Ventricular Septal Defect

Membranous ventricular septal defect:

The membranous septum is very small, therefore ventricular septal defects usually extend into the surrounding muscle septum, this is called perimembranous ventricular septal defect. This kind of ventricular septal defect is very close to the tricuspid valve septal leaflets which may be damaged by shunting across the defect whether it is involved , or not in forming an aneurysmal pouch leading which may lead to ventricular septal defect closure. This type of ventricular septal defect is most common accounting for 75% of all ventricular septal defects. It is associated with malalignment of the outflow septum as in tetralogy of Fallot.

Muscular ventricular septal defect:

This is the second most common type of ventricular septal defects. It might be in the apical portion or mid portion, either anteriorly or posteriorly. These ventricular septal defects may be single but appear as multiple from the right ventricular side.

Outflow tract ventricular septal defect:

These affect the outflow tract septum, it has the tendency to cause aortic valve cusp damage, which may lead to aortic regurgitation, this is more common in the oriental population.

Endocardial cushion type:

This is the least common type of ventricular septal defects, is located underneath the tricuspid valve. It may be associated with superior axis deviation on electrocardiography.


Patent Ductus Arteriosus

The ductus arteriosus originates embryologicaly from the left aortic arch artery therefore it connects the left pulmonary artery to the aortic arch opposite to the left subclavian artery. Patent ductus arteriosus when it closes it usually does so beginning from the pulmonary artery end, leaving a diverticulum in the aortic site which eventually closes. The patent ductus arteriosus goes into the left pulmonary artery even in right aortic arch. Rarely does it originates from the right pulmonary artery. In tetralogy of Fallot the patent ductus arteriosus is usually absent or small. In pulmonary atresia the patent ductus arteriosus is small because in-utero the blood shunts left-to-right in small volumes to the lungs. In premature babies the patent ductus arteriosus closes later than it would in term babies. However, if the prematurity is taken into consideration it closes about the same time. Patent ductus arteriosus closes with high oxygen tension which explains why at high altitude the patent ductus arteriosus remain patent for a longer time. Oxygen concentration above atmospheric level does not assist in closing the patent ductus arteriosus faster then it would naturally. The etiology of higher incidence of patent ductus arteriosus in maternal rubella infection is not clear but it could be due to tissue changes in the ductus arteriosus similar to those observed in right pulmonary artery and left pulmonary artery branches. Indomethicin if given to the mother at pre-term will cause the patent ductus arteriosus to constrict. This is due to interference with the arachidonic derivative causing lack of Prostaglandin. Supplemental oxygen will cause the patent ductus arteriosus to close in full term but not in premature babies. On the other hand, prostaglandin is better at keeping the patent ductus arteriosus open in premature babies versus full term babies. Polycythemia in patent ductus arteriosus with pulmonary vascular obstructive disease and right-to-left shunting tends to be more so than other cyanotic congenital heart disease. This is thought to be because of increased cyanotic blood flow to the kidneys triggering the mechanism for polycythemia.


Atrio-Ventricular Canal Defect

The ventricular septal defect can be very large extending beyond what endocardial cushion contributes to the ventricular septum. It is rare for a ventricular septal defect to be present with small primum atrial septal defect and even more rare without an atrial septal defect. The atrial septal defect is very variable in size. Primum atrial septal defect is seen with no VSD or a tiny inlet VSD. Cleft mitral valves are seen with primum atrial septal defect. A double inlet mitral valve is sometime noted with primum atrial septal defects. Tricuspid valve may override the ventricular septum when chordea insert into the left ventricle causing right atrial output to be directed into the left ventricle which may lead to hypoplasia of the right ventricle. The left ventricular papillary muscles may be single or close to each other causing mitral stenosis. AV canal defect is present in 50% of all children with Downs syndrome and congenital heart disease. It is rare to have ventricular size discrepancy in children with AV canal and Down syndrome in comparison to other children with AV canal defect. Tetralogy of Fallot or pulmonary stenosis could also be present with AV canal defect. Other types of congenital heart disease are common with AV canal defects except in those with Down syndrome that tend to have either a straight forward AV canal defect or AV canal defect with Tetralogy of Fallot or pulmonary stenosis.

Types of AV canal:

  • Type A: The anterior leaflet is divided and attached to the crest of the VSD.
  • Type B: Anterior leaflet is divided and chordae from left sided leaflet crosses and inserts in the RV.
  • Type C: Anterior leaflet is ridging (single) with no chordal attachment (free floating).



Pulmonary Stenosis

The pulmonary valve leaflets may be fused or the valve leaflets may be thickened. The opening may be eccentric when the valve leaflets are thick, sometimes the leaflets are immobile with a variably small annulus. The right and left coronary arteries are usually dilated because of poststenotic jet effect. Right ventricular hypertrophy is proportional to the degree of stenosis. Right ventricular outflow tract obstruction may be noted due to muscular hypertrophy of the moderator band. This is usually seen in association with membranous ventricular septal defect, however, the septal defect may close leaving right ventricular outflow obstruction. It is not known if it is possible to develop this pathology without ever having had a VSD. Tetralogy-like pulmonary stenosis with intact ventricular septum is rare. Left and right pulmonary arteries hypoplasia together with pulmonary stenosis is seen after congenital Rubella syndrome. Diffuse pulmonary stenosis is seen with Alagille syndrome where there is pulmonary valve stenosis as well as diffuse main and branch pulmonary artery stenosis. Peripheral pulmonary stenosis is seen in Noonanís syndrome. Peripheral pulmonary stenosis and main pulmonary artery stenosis is seen with Williamis syndrome.


Aortic Stenosis

The commissures may be fused, the valve ring is occasionally hypoplastic. The orifice of the aortic valve could be eccentric. The valve is commonly bicuspid in aortic stenosis and the leaflets are asymmetric in 40% of cases. There is occasionally more than one level of obstruction in the left ventricular outflow tract or supravalvar area together with aortic stenosis. 10% of patients with aortic stenosis have subvalvar aortic stenosis. Supravalvar aortic stenosis is rarely associated with aortic stenosis. 50% of valvar aortic stenosis are associated with aortic insufficiency. Aortic stenosis most probably begets aortic stenosis rather than being a result of bicuspid aortic valve since bicuspid aortic valve is 10-20 times as common as aortic stenosis. Therefore, a small number of bicuspid valve will lead to aortic stenosis and the majority will not develop into aortic stenosis. Right-to-left commissures have worse prognosis in bicuspid aortic than anteroposterior commissures in developing aortic stenosis. Also eccentric orifices have worse prognosis than central orifices in developing aortic stenosis.


Subaortic Membrane

Discrete type:

Fibromuscular ridge, sometimes also called membranous ridge.
Close to aortic valve.
Orifice may be eccentric.
The aortic valve leaflets may be damaged by stenosis jet causing deformity and aortic insufficiency.
It is commonly associated with coarctation, interrupted aortic arch, VSD as well as defects of the mitral valve.
This lesion is usually overlooked in infancy.

The tunnel type:

A variety of fibromuscular ridge but with some length approximately 1 cm.
Because of its length the mitral valve is involved.
Hypertrophic subaortic stenosis:
Due to hypertrophic cardiomyopathy with asymmetrical hypertrophy of the interventricular septum.

Obstructive bulbo-ventricular foramen:

Due to small outlet chamber, for example, d-transposition of the great arteries with small subaortic chamber and restrictive VSD (bulbo ventricular foramen).

Accessory endocardial cushion tissue:

Due to accessory tissue from the common AV valve leaflet or bridging leaflet in the LVOT causing obstruction.


Coarctation of the Aorta

Embryology: One theory suggests decreased blood flow in the aorta leading to coarctation, another theory proposes that coarctation is the result of a lasso ring of ductal tissue surrounding the aortic arch, consequently restricting after birth leading to coarctation of the aorta. Or coarctation of the LPA in patients with pulmonary atresia or critical pulmonary stenosis with in-utero left-to-right shunting at the PDA due to ductal tissue which may lasso the LPA leading to LPA stenosis after birth.

Coarctation of the aorta could be associated with multiple stenotic lesions of the left heart as seen in Shones syndrome.

Narrowing could be proximal or distal to the PDA. As the narrowing becomes significant more and more collaterals develop. The amount of collaterals may be so large that it will decrease any pressure gradient across the coarctation and lower extremity blood pressures will be close to the upper extremity blood pressures. Pressure gradient across the coarctation may be more than the difference between the upper and lower extremity blood pressure due to collateral vessels bypassing the area of coarctation.


Tertralogy of Fallot

The ventricular septal defect is located in the membranous septum, it is subaortic and sometimes extends to the subpulmonic valve area. The VSD is large causing equalization of LV and RV pressures. These defects do not usually get smaller and are not known to close spontaneously. The right ventricular outflow tract is hypoplastic and almost always obstructive. Occasionally at birth the RVOT shows no significant obstruction and results in the so-called "pink" tetralogy of Fallot. Mild hypertrophy of the moderator band and ventricular septal defect should be distinguished from tetralogy of Fallot as the prognosis is different in each case. The pulmonary valve annulus is typically small in tetralogy of Fallot and the leaflets are deformed. The main pulmonary arteries in contrast to pulmonary stenosis is small as well as the branch pulmonary arteries. There might be branch pulmonary artery stenosis as well as peripheral pulmonary artery stenosis in addition to the RVOT and pulmonary valvar stenosis. Bronchial arterial collaterals are sometimes present which connect to the peripheral pulmonary arteries. The main pulmonary artery is occasionally atretic and the pulmonary arteries are fed either by patent ductus arteriosus or collateral vessels. The aortic valve is typically large.

Ten per cent (10%) of tetralogy of Fallot patients have pulmonary atresia. Of those patients, 70% have the pulmonary arteries fed by patent ductus arteriosus and 30% by collateral. In patients who have collateral blood vessels supplying the pulmonary arteries the pulmonary arteries may be significantly small which would necessitate utilizing the collaterals in a unifocalization process. Forty per cent (40%) of patients with tetralogy of Fallot have patent foramen ovale and 25% have a right aortic arch. As the incidence of anomalous coronaries are also higher in patients with tetralogy of Fallot than the normal population where it is seen in 5%. The left anterior descending artery might originate from the right coronary artery and pass in front of the right ventricular tract which is an important thing to know since the surgeon may attempt opening the RVOT and causing damage to the left anterior descending artery.


Tetralogy of Fallot with Absent Pulmonary Valve

This is an uncommon variation of tetralogy of Fallot. The pulmonary valve leaflets are represented by nubbins of tissue. The clinical picture is dominated by pulmonary insufficiency rather than pulmonary stenosis.

The anatomy is the same as tetralogy of Fallot except that the right ventricular outflow tract is not excessively restrictive. The pulmonary arteries are dilated and sometimes aneurysmal. The pulmonary artery dilatation may extend beyond what is expected from pulmonary insufficiency to several generations of pulmonary arteries causing bronchial constrictions.



Pulmonary Atresia with Intact Ventricular Septum

The pulmonary valve annulus is usually small but not hypoplastic. The pulmonary valve leaflets are well formed but fused. The main pulmonary artery is small but rarely is atretic as seen with pulmonary atresia and ventricular septal defect. The patent ductus arteriosus is usually small because it carries blood from aorta to pulmonary arteries in utero and not the other way around as in normal. Therefore, much less blood travels through the PDA in utero. The right ventricle might be of several types.

Type I is tripartite.

Type II bipartite (atretic body).

Type III unipartite (atretic body and infundibulum).

Tricuspid valve might be deformed and stenotic.

Sinus nodes from the right ventricle cavity to myocardium and from myocardium to coronary arteries. Collateral circulation from the descending aorta to pulmonary arteries is rare. Other congenital heart disease is rarely associated with this one. Right aortic arch is not known to occur in pulmonary atresia with intact ventricular septum.



Double Outlet Right Ventricle

Double outlet right ventricle is diagnosed when one great vessel and all or the majority of the other great vessels emerge from the right ventricle. The great vessels relationship to each other may be in any of the various possibilities but usually they are side by side and parallel. The aortic valve could be to the right or left of the pulmonic valve or in an anteroposterior relationship. Three-quarter of cases have pulmonary stenosis. The VSD could be subaortic, subpulmonic or non-committed or far away from the semilunar valves (as in muscular or AV canal type VSDís). Many other congenital anomalies may be present, for example, hypoplastic left heart, however, this would be with good aortic valve size and ascending aorta and mitral atresia may sometimes be present.

Three types of great vessels arrangement are observed:

The aorta to the right and posterior of the pulmonary valve, the two great vessels intertwine, i.e., normal relationship. This is the most frequent.

The aorta and pulmonary artery are side by side and the great vessels are parallel without intertwining. The aorta is to the right of the pulmonary artery. This is the second most common and also known as the Taussig-Bing variety.

Great vessels are again parallel with aorta to the left. This is the lest common. The VSD and double outlet right ventricle does not change in its location, however, it is in between the two arms of the tribiculo-septal marginalis. The anatomy of the great vessels and conal tissue determine to which arterial valve the VSD is committed.

Taussig-Bing Anomaly:

This is double outlet right ventricle with aortic valve being anterior and to the right of the pulmonary valve, i.e., transposition of the great vessels arrangement. The great vessels are parallel to each other. The VSD is subpulmonic and there is no pulmonary stenosis.

VSD in double outlet right ventricle could be muscular or of the AV canal type and therefore non-committed to any arterial valve.

When the great vessels are normally related the line dissecting the short axis of the arterial valves is parallel to the interventricular septum. Therefore the outlet septum is perpendicular to the interventricular septum and if the outlet septum is well formed and fuses with the interventricular septum this will lead to subaortic VSD but if the outlet septum is hypoplastic than the VSD will be doubly committed.

When the great vessels are of the Taussig-Bing variety the line dissecting the short axis of the arterial valve is perpendicular to the interventricular septum and the infundibulum fold fuses with the interventricular septum and this will determine if the VSD is committed to the pulmonary artery (well fused fold and trabeculoseptal marginalis) were doubly committed (no fusion). Therefore, if the great vessels are normally related a VSD could be subaortic or doubly committed and if great vessels are transposed then the VSD is subpulmonic or doubly committed. The boundaries of the VSD is important to the surgeon since the posterio-inferior border of the VSD may be muscular (when the ventriculo infundibulum both fuses with the trabeculoseptal marginalis) therefore making it safe for the surgeon to close the VSD. However, if these structures are not fused the conduction system will lie close to the rim of the VSD and therefore there is increased risk of AV block when VSD baffle is placed.


Transposition of the Great Arteries

The aorta is anterior and slightly to the right of the main pulmonary artery. The aortic valve is to the right of the pulmonary valve but still anterior to it. The main pulmonary artery is in such a position with the left ventricle allowing direct flow into the right pulmonary artery and it will consequently become larger and more flow to the right pulmonary artery and right lung. Most infants have patent foramen ovale and a patent ductus arteriosus. Fifty per cent (50%) of patients with TGA have ventricular septal defects and 50% have an intact ventricular septum. Pulmonary stenosis is the most commonly associated cardiac defect with transposition of the great vessels. Next are anomalies of the tricuspid valve, then coarctation of the aorta. These anomalies are more commonly associated in transposition of the great vessels with ventricular septal defect and with an intact ventricular septum.

Pulmonary stenosis in patients with transposition of the great arteries particularly those with VSD is due to leftward bowing of the ventricular septum and close proximity of the mitral valve to the ventricular septum leading to dynamic obstruction. Anatomical valvar or valvar PS are rare. One-third (1/3) of patients with d-TGA and VSD will have closure of the VSD in the first year of life. The VSD could be located anywhere in the septum with no particular location more frequently than in patients without d-TGA.

Coronary arteries 60% of patients have a right coronary artery emerging from a right coronary sinus and a left coronary artery which gives the circumflex and left anterior descending coming from the left coronary sinus. In 10% of patients the right coronary artery and the circumflex emerge from the right coronary sinus with the left anterior descending emerging from the left coronary sinus. In these cases the circumflex travels posterior to the pulmonary artery.

In another 10% of the patients the circumflex emerges from the right coronary sinus and the right coronary artery and left anterior descending emerge from the left coronary sinus. The right coronary artery will travel rightwards anterior to the aorta.

In another 10% of patients the right coronary artery emerges from the right coronary sinus and gives the right coronary artery and the left coronary artery. The left coronary artery will travel in between the aorta and the pulmonary artery and give this circumflex and the left anterior descending branches.

The drop in the pulmonary vascular resistance soon after birth will increase the pulmonary blood flow through the PDA and this will result in dilation of the left atrium and stretching of the patent foramen ovale with shunting of blood from the left atrium to the right atrium across the stretched patent foramen ovale. This will allow mixing of blood and better oxygen saturation. Patients with ventricular septal defects tend to have better mixing of the pulmonary and systemic circulations. Patients with a VSD may become more cyanotic as the VSD gets smaller. Patients with an intact ventricular septum tend to have dynamic LVOT obstruction usually reversible after arterial switch operation. Patients with an anatomic left ventricular outflow tract obstruction tend to have better left-to-right shunting in the VSD and less cyanosis than others. d-TGA with intact ventricular septum are best repaired after 1-2 weeks from birth because a drop in the pulmonary vascular resistance will cause deconditioning of the left ventricle making repair difficult at that point. Shunting at the ASD, VSD and PDA are typically as following:

ASD: Left-to-right shunting is in systole and right-to-left in diastole.

VSD: Left-to-right shunting in diastole and right-to-left shunting in systole.

PDA:  Left-to-right shunting in diastole and right-to-left shunting in systole.


Ebstein's Anomalies

There is adherence of the posterior and septal leaflets to the myocardium with apical displacement of effective orifice. Anterior leaflet becomes redundant and fenestrated. The portion of the right ventricle that becomes incorporated into the right atrium because of the apical displacement of the tricuspid valve orifice become atrialized and the annulus of the tricuspid valve become dilated.

Normally, there is some apical displacement of the affected tricuspid valve orifice which should be less than .8 cm/M2 of the body surface area. In mild cases the tricuspid valve leaflets are normal appearing with only mild apical displacement. In moderate to severe cases the leaflets are thick, nodular and focally muscularized and attached to the underlying muscular wall. The chordae of the tricuspid valves are either very few or absent. In most severe cases the whole right ventricular inlet portion is atrialized.


Hypoplastic Left Heart Syndrome

The left ventricle is small with or without mitral atresia and with or without aortic valve atresia.

The ascending aorta may be as small as 2 mm but enough to supply coronary arteries in a retrograde fashion. The PDA is large shunting right-to-left. Babies are not born with coarctation but it frequently develops. A patent foramen ovale could be small or even closed.