Cardiology - Congenital heart disease

Question 1

What is the definition of congenital heart disease (CHD)?

Answer 1

CHD is an abnormal embyrological cardiac development, or persistence of some parts of the fetal circulation after birth, resulting in structural cardiac defects.

The incidence of major defects is 8/1000 live births. Minor defects are more common, e.g. bicuspid aortic valve affects 2%.

Question 2

How is congenital heart disease classified?

Answer 2

Classification of CHD is divided into 3 groups:
1) Shunts = communications between the right and left heart

2) Valvular defects = abnormal valve development, usually resulting in valvular stenosis or atresia (= total absence of a valve orifice)
- aortic or pulmonary stenosis
- bicuspid aortic valve; predisposes to later aortic stenosis
- tricuspid atresia

3) Complex lesions = combinations of valvular defects, septal defects, often with failure of normal great vessel and/or cardiac chamber development
- Fallot’s tetralogy
- transposition of the great vessels
- Ebstein’s anomaly

Question 3

How common are ventricular septal defects?

Answer 3

VSD comprises 25% of CHD. A defect in the interventricular septum allows systolic blood flow from the left to right ventricle (due to the pressure difference present between blood in the 2 chambers). Although more common at birth, most VSDs close spontaneously in childhood, so that the overall incidence in adults is lower than that for ASDs. Only 20% of VSDs occur in isolation; most are associated with other cardiac abnormalities.

Question 4

How is the size of a VSD related to its clinical effects?

Answer 4

A small defect produces very high velocity jets and a loud murmur (maladie de Roger) that is not of haemodynamic significance.

Large defects may have a quiet murmur and a large left to right shunt. Untreated this may cause pulmonary hypertension and Eisenmenger’s syndrome. Treatment is surgical closure before pulmonary hypertension develops.

There is a high risk of endocarditis (especially in small defects) so antibiotic prophylaxis is essential.

Question 5

Where is the most common site for a VSD to develop?

Answer 5

VSDs can either be - membranous, infundibular or muscular.

The ventricular septum is usually formed by the fusion of a muscular ridge that grows upwards from the apex of the heart to a thinner membranous partition that grows downwards from the endocardial cushions.The basal (membranous) region is the last part of the septum to develop and is the site of approximately 90% of VSDs.

Question 6

What is an atrial septal defect?

Answer 6

ASDs comprise 10% of CHD. A defect in the interatrial septum allows shunting of blood from the left to the right side of the heart. The secundum type of ASD is most commonly, accounting for 70% of cases.

Primum ASD accounts for 30% and often involves the atrioventricular valves with mitral or tricuspid regurgitation. These may be associated with other defects including VSD.

Question 7

How does the interatrial septum develop? What is the difference between an ASD and a patent foramen ovale?

Answer 7

During normal cardiac development, patency is maintained between right and left atria by a series of ostia (primum and secundum) that eventually become the foramen ovale. This arrangement allows oxygenated blood from the maternal circulation to flow from the right to the left atrium thereby sustaining the fetus. At later stages of development, tissue flaps (septum primum, septum secundum) grow to occlude the foramen ovale and in 80% of cases, the higher left sided pressures in the heart that occur at birth permanently fuse the septa against the foramen ovale. In the remaining 20% of cases a patent foramen ovale results.

Although the flap is of adequate size to cover the foramen, the unsealed septa can potentially allow transient right to left blood flow. Paradoxical embolism, defined as venous emboli (e.g. from the deep veins) that enter the arterial circulation may also occur if right sided atrial pressures increase, such as with pulmonary hypertension or a Valsalva manourver. In contrast to a patent foramen ovale, an ASD is an abnormal FIXED opening in the atrial septum that allows unrestricted blood flow between the atrial chambers. A majority (90%) of ASDs are so called ostium secundum defects in which growth of the septum secundum is insufficient to occlude the second ostium.

Question 8

What are the clinical features of ASDs?

Answer 8

Left to right shunting increases pulmonary blood flow, producing a systolic pulmonary flow murmur, wide fixde splitting of the second heart sound and right ventricular hypertrophy (RVH). An ECG shows right bundle branch block (RBBB) with right axis deviation and RVH (secundum) or left axis deviation with RVH (primum). Supraventricular tacchycardias - e.g. AF - are common. ASDs may be undetected until adult life when they present with exertional dyspnoea and fatigue. The diagnosis is confirmed by transoesophageal cardiac ultrasound. Treatment is closure of the defect, either by surgery or by percutaneous closure device.

Question 9

Can blood flow through an ASD reverse?

Answer 9

ASDs initially cause left to right shunts, as a consequence of the lower pressures in the pulmonary circulation and the right side of the heart. In general, these defects are well tolerated, especially if they are less than 1 cm in diameter. Even larger lesions do not usually produce any symptoms in childhood. Over time however, chronic volume and pressure overloads can cause pulmonary hypertension.

A general rule with shunt pathophysiology is as follows. If an ASD, VSD or PDA is mild-moderate then left to right shunts occur which increases pulmonary blood flow. The right heart enlarges and hypertrophies as PA pressure rises.

If the shunts are large, irreversible pulmonary hypertension plus right to left shunting (leading to cyanosis) may occur.

Question 10

What is a patent ductus arteriosus (PDA)?

Answer 10

PDA comprises 15% of CHD and is another form of left to right shunt. The ductus arteriosus fails to close after birth resulting in left to right shunting from the aorta to the pulmonary artery and a continuous (machinery) murmur. A large duct with a significant shunt leads to left ventricular hypertrophy (LVH) and heart failure, or pulmonary hypertension and Eisenmenger’s syndrome. Duct endocarditis is a significant long term risk.

Question 11

How is PDA treated?

Answer 11

Treatment in neonates involves indomethacin blockade of prostaglandin production, which may provoke duct closure. Ducts remaining open require surgical ligation or percutaneous closure (coil or umbrella devices). Generally speaking, isolated PDAs should be closed as early in life as is feasible, but preservation of ductal patency (by administering prostaglandin E) can be lifesaving when a PDA is the only means to sustain systemic or pulmonary blood flow (e.g. in infants with aortic or pulmonic atresia).

Question 12

What is Eisenmenger’s syndrome?

Answer 12

This describes irreversible pulmonary hypertension (from the high pulmonary blood flow of large left to right shunts) with shunt reversal (from left to right, to right to left) resulting from high right sided heart pressures. Patients experience worsening symptoms with breathlessness, there is cyanosis, clubbing and signs of severe pulmonary hypertension. Surgical closure of left to right shunts must be undertaken before Eisenmenger’s syndrome develops. The only surgical treatment for established Eisenmenger’s syndrome is heart-lung transplantation.

Question 13

What is an important feature of right to left shunts?

Answer 13

Cardiac malformations associated with right-to-left shunts are distinguished by early cyanosis. This occurs because poorly oxygenated blood from the right side of the heart flows directly into the arterial circulation. Cyanotic heart diseases all have T in their names (as opposed to D’s which denotes left to right shunting). Two of the most important conditions associated with cyanotic congenital heart disease are tetralogy of Fallot and transposition of the great vessels. Clinical consequences of severe, systemic cyanosis include clubbing (hypertrophic osteoarthropathy), polycythaemia, and paradoxical embolisation.

Question 14

What is tetralogy of Fallot?

Answer 14

This is the most common “complex” CHD (10% of CHD), involving a combination of VSD with right to left shunting, due to:

• pulmonary stenosis, either infundibular or valve
• right ventricular overload and hypertrophy
• dextro position of the aorta so that it overrides the VSD

Question 15

What are the clinical features of tetralogy of Fallot?

Answer 15

There is cyanosis, clubbing, signs of RVH and a pulmonary systolic murmur (the large VSD does not generate a murmur). Children with Fallot’s tetralogy experience exertional breathlessness, dizziness and growth retardation.

Squatting kinks the femoral vessels, increasing systemic vascular resistance and reduces the right to left shunt.

Question 16

How is tetralogy of Fallot treated?

Answer 16

Surgery is the mainstay of treatment. It aims to:

• totally correct the defects, if the pulmonary arteries are large enough
• alternatively, pulmonary blood flow is increased using systemic to pulmonary artery shunts - e.g. Blalock-Taussig (subclavian artery to pulmonary artery), Waterston’s shunt (ascending aorta to right pulmonary artery), Pott’s shunt (descending aorta to left pulmonary artery)

Question 17

What is the main cause of tetralogy of Fallot?

Answer 17

All the cardinal features of ToF result from anteriorsuperior displacement of the infundibular septum leading to abnormal septation between the pulmonary trunk and the aortic root.

Question 18

Describe the morphology of the heart in tetralogy of Fallot?

Answer 18

The heart is large and “boot shaped” as a consequence of right ventricular hypertrophy. The proximal aorta is usually dilated while the pulmonary trunk is hypoplastic. The left sided cardiac chambers are of normal size, while the right ventricular wall is markedly hypertrophic, sometimes exceeding even the thickness of the left ventricular wall. The VSD is usually large, and normally in the membranous portion of the interventricular septum. The aortic valve lies immediately over the VSD (overriding aorta) and is the major site of egress for blood from both ventricles. The obstruction of the right ventricular outflow tract most often is due to narrowing of the infundibulum (subpulmonic stenosis) but can also be caused by pulmonary valve stenosis or complete atresia of the valve and the proximal pulmonary arteries. In such cases, a PDA or dilated bronchial arteries may be the only route for blood to reach the lungs.

Question 19

Why do the clinical features of ToF depend on the degree of pulmonary outflow obstruction?

Answer 19

The haemodynamic consequences of ToF are right to left shunting, decreased pulmonary blood flow and increased aortic volumes. If pulmonary obstruction is mild, the condition resembles an isolated VSD because high left sided pressures cause only a left to right shunt with no cyanosis. More commonly, more severe degrees of pulmonic stenosis cause early cyanosis. As the child grows and the heart size increases, the pulmonic orifice does not expand proportionately, leading to progressive worsening of functional stenosis.

Question 20

Do patients with ToF tend develop pulmonary hypertension?

Answer 20

Pulmonic outflow stenosis protects the pulmonary vasculature from pressure and volume overloads, so that pulmonary hypertension does not develop and right ventricular failure is rare. Nevertheless, patients develop the typical sequelae of cyanotic heart disease, such as polycythaemia with hyperviscosity, hypertrophic osteoarthopathy. Right to left shunting also increases the risk of infective endocarditis and systemic embolisation.

Question 21

What is Ebstein’s anomaly?

Answer 21

The tricuspid valve is displaced downwards into the right ventricle, resulting in a very small right ventricular cavity and a very large right atrium. There is tricuspid regurgitation and usually an ASD; 20% have Wolff-Parkinson-White syndrome.

Question 22

What is transposition of the great vessels?

Answer 22

Transposition of the great vessels is a discordant connection of the ventricles to their vascular outflow tracts. The embryonic defect is an abnormal formation of the truncal and aortopulmonary septa so that the aorta arises from the right ventricle and the pulmonary artery from the left ventricle. The atrium to ventricle connections however, are normal.

Question 23

What is the functional outcome of transposition of the great vessels?

Answer 23

Separation of the systemic and pulmonary circulations, a condition incompatible with post natal life unless a shunt such as a VSD exists for adequate mixing of oxygenated and deoxygenated blood to the aorta. VSDs occur in about 1/3 of cases.

There is marked right ventricular hypertrophy, since this chamber operates as the systemic ventricle, the left ventricle is atrophic, since it pumps only to the low resistance pulmonary circulation.

Some patients with transposition have a patent foramen ovale or PDA that allows oxygenated blood to reach the aorta, but these tend to close. As a result, such infants require emergency surgical intervention within the first few days of life.

Question 24

What are the clinical features of transposition?

Answer 24

The dominant feature is cyanosis, with the prognosis dependent on the magnitude of shunting, the degree of tissue hypoxia and the ability of the right ventricle to maintain systemic pressures. Without surgery (even with stable shunting) most patients with transposition of the great vessels die in the first few months of life.

Question 25

How is transposition treated?

Answer 25

Surgically.
- balloon septostomy (Rashkind): increases shunting and reduces cyanosis

• Intra-atrial shunt (Mustard or Senning operation): direct systemic venous return from the right heart across the ASD into the left ventricle, pulmonary venous return passes in the opposite direction and into the aorta
• Arterial switch operation: totally corrects the defect by reconnecting the aorta to the left ventricle and the pulmonary artery to the right ventricle
• Congenitally corrected transposition: the right and left ventricles and AV valves are interchanged (venous return drains via the right atrium into the morphological left ventricle, which ejects blood into the pulmonary artery). Usually well tolerated in childhood, but heart failure may occur in adult life (the morphological right ventricle cannot sustain pressures for long)

Question 26

How common is coarctation of the aorta?

Answer 26

Coarctation accounts for 5% of CHD and is a type of obstructive lesion. Coarctation means narrowing. Males are twice as affected as females although females with Turner’s syndrome more frequently have coarctation.

Question 27

What are the two forms of coarctation?

Answer 27

There are two classic forms: “infantile” form featuring hypoplasia of the aortic arch proximal to a PDA, and an “adult” form consisting of discrete, ridge like infolding of the aorta , adjacent to the ligamentum arteriosum.

Coarctation can occur as a solitary defect, but in more than half the cases it is accompanied by bicuspid aortic valve.

Question 28

What are the clinical features of coarctation of the aorta?

Answer 28

Clinical features depend almost entirely on the severity of the narrowing and the patency of the ductus arteriosus:
1) Preductal coarctation with a PDA - usually presents early in life, classically as cyanosis localised to the lower half of body; without intervention, most affected infants do not survive the neonatal period

2) Postductal coarctation without a PDA - is usually asymptomatic and the disease may go unrecognised into adult life. Classically, there is upper extremity hypertension paired with weak pulses (radio-femoral delay) and relative hypotension in the lower extremities, associated with symptoms of claudication and coldness. Exuberrant collateral circulation around the coarctation often develos through markedly large intercostal and internal mammary arteries; expansion of blood flow through these vessels can lead to radiologically visible “notching” of the ribs

In most cases, significant coarctations are associated with systolic murmurs and occasionally palpable thrills. Balloon dilation or surgical resection with end to end anastomosis (or replacement of the affected aortic segment by prosthetic graft) provide good results.