Ventricular Septal Defects

Ventricular septal defect is failure of development of the septum between the two ventricles of the heart. The ventricles are a single chamber at about 4 weeks gestation but by 8 weeks it has been divided in two. Failure of development of any part of the septum results in a defect. It may vary considerably in terms of size and haemodynamic consequences.

There are a number of classifications of VSDs but the following is generally accepted as the most useful for both clinical and surgical purposes:

• Perimembranous, also called infracristal VSDs lie in the left ventricular outflow tract just below the aortic valve. These account for 80% of all VSDs. They have been subclassified as:
  • Perimembranous inlet
  • Perimembranous outlet
  • Perimembranous muscular
• Supracristal defects are also called conal, infundibular, subpulmonary, subarterial and outlet and comprise 5 to 8% of isolated VSDs but in Japan the figure is 30%. The defect lies beneath the pulmonary valve and communicates with the right ventricular outflow tract above the supraventricular crest and is associated with aortic regurgitation due to prolapse of the right aortic cusp. This occurs in only around 5% of outlet VSDs except in Japan where it may occur in as many as 50%.
• Muscular or trabecular VSDs are bounded entirely by muscular septum and are often multiple. Hence the term Swiss cheese septum for multiple holes. Other subclassifications depend on the location. These account for 5 to 20% of all defects.
• Posterior, also called canal-type, endocardial cushion-type, AV septum-type and inlet VSDs lie posterior to the septal leaflet of the tricuspid valve. It is not associated with defects in the AV valves and it accounts for 8 to 10% of VSDs.
• Acquired VSD can occur as a result of a septal myocardial infarct but such a finding is much rarer than congenital lesions and prognosis tends to be poor.¹

• Some form of anomaly of the heart or great vessels is present in about 8 per 1,000 live births and of these around 50% are VSD, either alone or in association with other anomalies. The best known serious anomaly in which VSD is just a part is Fallot's tetralogy of right ventricular outflow obstruction, VSD, aortic root overrides the VSD and there is subsequent right ventricular hypertrophy.
• Isolated VSD accounts for 20% of congenital heart disease. There is a slight female preponderance at about 55%:45%.
• It is possible that the true incidence is higher than thought and many small defects are undetected and either close spontaneously or cause no trouble in life.

There are a number of chromosome abnormalities that are associated with VSD although they account for less than 5% of the total. They especially include the trisomies, Edwards' syndrome, Patau's syndrome and Down's syndrome. Where antenatal diagnosis has shown a VSD, it is reasonable to proceed to fetal karyotyping in case of chromosomal abnormality.² It has been suggested that deletion of part of chromosome 22q11 should be sought.³ This is the chromosome abnormality of Di George's syndrome in which there is maldevelopment of the 3rd and 4th branchial arch so as to produce failure of development of the parathyroids causing hypocalcaemia and thymic aplasia causing lack of T lymphocytes.⁴ VSD is 3 times more likely if a sibling has the condition but even in identical twins the discordance is high. About 3% of offspring of those with VSD will also have the condition.⁵ VSD is also more likely with diabetes in pregnancy.⁶ It can occur with fetal alcohol syndrome.⁷ There may be an association with maternal use of cannabis.⁸

This will depend upon the severity of the lesion:

• Small lesions will cause little or no symptoms. Feeding and weight gain is normal and the lesion may be detected when a murmur is heard at a routine examination.
• With moderate size defects, early symptoms include tachypnoea with increased respiratory effort, excessive sweating due to increased sympathetic tone, and fatigue when feeding. Feeding is exercise for a baby and a detailed feeding history is important. Poor weight gain is a good indicator of heart failure in a baby. The typical findings are that the baby is of a normal length but of low weight. These features usually begin between 4 and 6 weeks of age when the pulmonary resistance starts to fall but they occur earlier in premature babies. Respiratory infections may occur and increased pulmonary venous pressure can produce pulmonary oedema.
• With large VSDs the features are similar but more severe. If there is cyanosis it suggests a more severe and complex condition such as Fallot's tetralogy but acquired cyanosis may represent a very serious complication with pulmonary hypertension and a right to left shunt causing an Eisenmenger syndrome.

Again these are dependent upon the severity of the lesion with, however, the exception of the murmur. Murmurs are caused by turbulence of blood flow. There may be more turbulence with a small hole than with a large defect. The loudness of the murmur gives no indication of the size of the lesion. Even the adage that the louder the sound, the smaller the lesion is untrue.

• In mild disease there may be very little abnormality. The precordial impulse may be greater than usual. If it can be heard, the physiological splitting of the second sound is normal but there is a harsh systolic murmur that is best heard at the left sternal edge that may obliterate the second sound. The murmur tends to be throughout systole but if the defect is in the muscular portion it may be shorter as the hole is closed as the muscle contracts.
• With a moderate lesion there is enhanced apical pulsation as well as a parasternal heave. There will be a systolic murmur, perhaps with a thrill. A thrill is simply a palpable murmur. A prominent third sound with a short early mid-diastolic rumble is audible at the apex when pulmonary blood flow is twice the systemic flow or greater. S2 is usually more narrowly split with an enhanced P2.
• With a large lesion there may be a right to left shunt and with it central cyanosis and clubbing of the fingers. There is a prominent right ventricular heave. The systolic murmur may be short or absent. S2 is loud and there may be a right ventricular S3. Children with cyanotic congenital heart disease like to squat. This is a typical feature of Fallot's tetralogy.

This is usually a harsh murmur that is uniform throughout systole right up to the normally split S2.

Again the degree of abnormality will depend upon the severity of the lesion.

• In significant disease, CXR will show an enlarged heart and more prominent pulmonary vascular markings. An enlarged left atrium may be visible in a lateral film. With more severe disease there may be evidence of right ventricular hypertrophy. If there is a marked increase in pulmonary vascular resistance, the heart may be more normal in size and the peripheral vascular fields not abnormal.
• Nowadays echocardiography can provide much information that previously required cardiac catheterisation. Two-dimensional echocardiography, along with Doppler echocardiography and colour flow imaging can assess the size and location of virtually all VSDs. Doppler echocardiography also provides physiological information including right ventricular pressure, pulmonary artery pressure and the difference in pressure between the ventricles. Measurement of left atrial and left ventricular diameter provides semi-quantitative information about shunt volume. Defect size is often given in terms of the size of the aortic root. Defects that are about the size of the aortic root are classified as large, those one third to two thirds of the diameter of the aorta are moderate, and those less than one third of the aortic root diameter are small.
• Measurement of left atrial and left ventricular diameter provides semi-quantitative information about shunt volume. Defect size is often expressed in terms of the size of the aortic root. Defects that approximate the size of the aortic root are classified as large, those one third to two thirds of the diameter of the aorta are classified as moderate, and those less than one third of the aortic root diameter are classified as small.
• ECG findings are often normal with a small lesion. With moderate or large shunts there is left ventricular hypertrophy but there may be biventricular hypertrophy. If pulmonary arterial pressure is high there may be no left ventricular hypertrophy but right ventricular hypertrophy. Large defects may involve the conducting tissue and left axis deviation occurs.
• It is only if the above investigations have failed to clarify the anatomy that cardiac catheterisation is required.
• In cyanosis there is polycythaemia and a high haematocrit.
• In terms of differentiating a pathological from a physiological murmur, the ECG appears to add nothing and the echocardiogram makes the paediatric cardiologist change his opinion very rarely.⁹

The main differential diagnosis is with patent ductus arteriosus and pulmonary stenosis. It is important to distinguish a VSD from an innocent physiological murmur.

• Irrespective of the size of the lesion, subacute bacterial endocarditis remains a potential problem until the defect is closed either surgically or spontaneously and antibiotic prophylaxis for at-risk procedures is required along the lines laid out in Aortic Valve Disease or Mitral Valve Disease. After closure of the defect the use of antibiotics to cover at risk situations should be continued for a further 6 months.
• With a small lesion the prognosis is excellent and no intervention is required beyond antibiotic prophylaxis where indicated.
• In moderate size lesions a trial of furosemide, ACE inhibitor and digoxin may suffice.
• Surgical repair is required if:
  • There is uncontrolled heart failure, including poor growth. Even very small babies may be considered
  • If the pulmonary artery pressure is raised then repair may be considered before the first birthday
  • Even with normal pulmonary artery pressure, if the ratio of aortic flow: pulmonary flow exceeds 2:1, then repair is required.
• Minimally invasive techniques of video-assisted cardioscopy to undertake repair are so far very promising.¹⁰
• Transcatheter techniques are also looking promising and avoid cardiopulmonary bypass.¹¹

Post-operative problems can occur:

• A small residual VSD (not uncommon). Depending upon heart size, symptoms and degree of shunting it may be necessary to re-operate.
• Right bundle branch block may be caused by operative trauma and occasionally complete heart block can occur. This has a late mortality.
• Ventricular dysfunction and ventricular arrhythmia can be a problem.

• If left untreated, there is enormous variation in outcome ranging from spontaneous closure to congestive cardiac failure and death in infancy.
• Spontaneous closure is common in children under a year old and rare over 2 years old. After more than six years almost a third of all perimembranous and just over two thirds of all muscular defects close spontaneously.¹² Outlet VSDs have a low incidence of spontaneous closure, and inlet VSDs do not close.
• Especially in those with cardiomegaly, arrhythmia and sudden death can occur.¹³
• Emphasise the need for good dental hygiene.
• As children with the perimembranous type grow older, the risk of aortic valve prolapse and regurgitation increases.
• Haemoptysis tends to develop between the ages of 25 and 40.
• The current surgical mortality rate is 3% for single VSDs and 5% for multiple VSD repair.

Exercise

If there is a small VSD and a normal heart otherwise, there is no restriction on exercise. After closure, normal exercise is permitted if there is normal pulmonary arterial pressure, no significant disturbance of rhythm during stress testing and ambulatory 24 hours monitoring, normal ECG and no evidence on echocardiography of aneurysm of the septal wall.

Contraception and reproduction

Improvement in the management of congenital heart disease has meant that congenital heart disease in adults is a growing problem and a recent paper from Holland suggested that prognosis to help assess risks for pregnancy and life assurance require further investigation.¹⁴ Combined oral contraceptives must not be used in primary pulmonary hypertension and should probably be avoided in VSD with pulmonary hypertension but there are plenty of other alternatives. Even progestogen only pills should be used with care but contraceptive implants may provide lower levels of hormone. IUCDs are difficult to fit in the nulliparous and antibiotic cover for insertion is probably wise. There is still much that is uncertain about contraception in this increasing and important group. ACE inhibitors are highly teratogenic and must not be used if pregnancy is desired. Outcome of pregnancy tends to be good¹⁵ especially if the degree of heart failure is no more than NYHA I (New York Heart Association Functional Classification grade 1 or no symptoms and no limitation in ordinary physical activity¹⁶).

The first description of VSD is usually attributed to Roger who published in 1879 at the age of 70. He was a French paediatrician who lived from 1809 to 1891 and his work centred on auscultation of the heart. The small defect is still called Maladie de Roger in remembrance of him. He was not the first to describe the condition but he was the first to produce clinico-pathological observations.

Eisenmenger described a patient with VSD, pulmonary hypertension and cyanosis in 1898. Victor Eisenmenger was an Austrian physician who lived from 1864 to 1932.

The earliest surgical treatment of VSD was pulmonary artery banding. Lillehei and colleagues in Minnesota first repaired a VSD in 1954 by controlled cross circulation with an adult as an oxygenator. The aorta was not clamped to avoid cardiac ischaemia.
In 1956, 20 patients at the Mayo clinic had closure of large VSDs, using a mechanical pump oxygenator. In 1961, Kirklin and colleagues reported primary repair of VSD in infants. Okomoto and associates, in 1969, used the technique of profound hypothermia with surface cooling, total circulatory arrest, and rewarming by a pump oxygenator in infants with VSD.
Routine primary repair of VSD in small infants is superior to pulmonary artery banding. Direct surgical repair using cardiopulmonary bypass is used in most centres today. Pulmonary artery banding, as part of a 2-stage procedure, tends to be reserved for critically ill infants with multiple VSDs or those with other anomalies too.