Ventricular septal defect

Ventricular septal defect (VSD) is the persistence of one or more holes in the septum that separates the left and right ventricles of the heart. The ventricles are a single chamber at about four weeks of gestation but by eight weeks it has been divided into 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. In adults a VSD may be acquired as a complication of myocardial infarction or trauma.

Classification¹

Classification of VSDs still remains a matter for debate. However, the most widely accepted classification which is useful both clinically and surgically describes VSDs based on their location in the ventricular septum.

• The ventricular septum is divided into a small membranous portion and a large muscular portion. The muscular septum has three components: the inlet septum, the trabecular septum, and the outlet (or infundibular) septum.

• Defects in the membranous septum often extend into different parts of the muscular septum and are labelled as perimembranous defects. These include inlet, trabecular and infundibular perimembranous defects. Perimembranous defects are the most common.

• Defects confined to the muscular septum are called muscular defects and further described according to their location in the muscular septum. Muscular defects can be found in or between the inlet septum, trabecular septum or infundibular septum.

• Defects in the area of the septum adjacent to the arterial valves are termed as subarterial infundibular defects. These defects are also called supracristal defects and because of the complete deficiency of the infundibular septum, allow prolapse of the aortic valve cusps into the right ventricular outflow tract. This can result in development of aortic regurgitation. These defects account for 5-7% of all defects in the western world but about 30% in far eastern countries.

• Inlet or AV canal VSDs lie beneath the septal leaflet of the tricuspid valve. They are not associated with defects in the atrioventricular (AV) valves and account for 5-8% of all 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 poor² .

Epidemiology³

• VSDs are the most common congenital heart defect in children, occurring in 50% of all children with congenital heart disease and in 20% as an isolated lesion.

• The incidence of VSDs has increased significantly with advances in imaging and screening of infants and ranges from 1.56 to 53.2 per 1,000 live births. The ease with which small muscular VSDs can now be detected has contributed to this increase in incidence.

• In the adult population VSDs are the most common congenital heart defect, excluding bicuspid aortic valve.

Associated conditions

Factors affecting the developing fetal heart can be associated with development of VSDs. These include genetic conditions (chromosomal, single gene or polygenic) as well as environmental influences.

• Chromosomal disorder caused by absent or duplicated chromosomes may be associated with VSDs. These include the trisomies (Edwards' syndrome, Patau's syndrome and Down's syndrome), 22q11 deletion and 45,X deletion (Turner syndrome). Recurrence risk in the offspring is that of the chromosomal disorder. If antenatal diagnosis has shown a VSD, it is reasonable to proceed to fetal karyotyping in case of chromosomal abnormality⁴ .

• Single gene disorders are caused by deletions, mutations or duplications within a single gene and there is high risk of recurrence in first-degree relatives. An example is Holt-Oram syndrome.

• Polygenic disorders encompass many congenital heart defects, including the majority of VSDs. No genetic testing is available but the recurrence risk can be used for genetic counselling for future pregnancies. The recurrence risk is estimated to be between 3% and 5%.

• VSD is also more likely with diabetes in pregnancy⁵ .

• It can occur with fetal alcohol syndrome.

• There may be an association with maternal use of cannabis⁶ .

Presentation

How haemodynamically significant a VSD is depends on its size, pressure in the individual ventricles and pulmonary vascular resistance³ . The presence of a VSD may not be obvious at birth because of nearly equal pressures in both the ventricles with little or no shunting of blood. As the pulmonary vascular resistance drops, the pressure difference between the two ventricles increases and the shunt becomes significant allowing the defect to become clinically apparent. An exception to this rule is Down's syndrome where the pulmonary vascular resistance may not fall and the VSD may not become clinically apparent, first presenting with pulmonary hypertension. All babies with Down's syndrome should therefore be screened for congenital heart disease no later than 6 weeks of age⁷ .

The clinical presentation varies with the severity of the lesion:

• With a small VSD, the infant or child is asymptomatic with normal feeding and weight gain and the lesion may be detected when a murmur is heard at a routine examination.

• With a moderate-to-large VSD, although the babies are well at birth, symptoms generally appear by 5-6 weeks of age. The main symptom is exercise intolerance and since the only exercise babies do is feeding, the first impact is on feeding. Feeding tends to slow down and is often associated with tachypnoea and increased respiratory effort. Babies are able to feed less, and weight gain and growth are soon affected. Poor weight gain is a good indicator of heart failure in a baby. Recurrent respiratory infections may also occur.

• With very large VSDs the features are similar but more severe. If appropriate management is not carried out promptly in infants with large VSDs, excessive pulmonary blood flow may lead to increase in pulmonary vascular resistance and pulmonary hypertension. These babies may develop a right-to-left shunt with cyanosis or Eisenmenger's syndrome.

Physical signs

Again, these depend on the severity of the lesion with, one exception, the loudness 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 'the louder the sound, the smaller the lesion' is untrue.

• With a small VSD the infant is well developed and pink. The precordial impulse may be greater than usual but is usually normal. 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, which 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 or large VSD there is enhanced apical pulsation as well as a parasternal heave. A grade 2 to 5/6 systolic murmur is audible at the lower left sternal border. It may be pansystolic or early systolic. A prominent third sound with a short early mid-diastolic rumble is audible at the apex with a moderate-to-large shunt (because of increased flow through the mitral valve during diastole). S2 is loud and single in patients with pulmonary hypertension.

• Large defects with no shunts or those with Eisenmenger physiology and right-to-left shunt may have no murmur.

Heart sounds

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

Investigations¹

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

ECG

• The ECG is usually normal in patients with small VSDs.

• With a moderate VSD, left ventricular hypertrophy (LVH) and occasionally left atrial hypertrophy (LAH) may be seen.

• With large VSDs the ECG shows biventricular hypertrophy (BVH) with or without LAH.

• In those with pulmonary hypertension, right axis deviation, right ventricular hypertrophy (RVH) and right atrial hypertrophy (RAH) may be seen.

CXR

• CXR is normal in patients with small VSDs.

• With larger defects cardiomegaly of varying degrees is present involving the left atrium, the left ventricle and sometimes the right ventricle. Pulmonary vascular markings are increased.

• In those who have developed pulmonary hypertension the main pulmonary artery and hilar pulmonary arteries are enlarged significantly but the peripheral lung fields are oligaemic and heart size is usually normal.

Echocardiography

• Transthoracic two-dimensional and Doppler echocardiography can identify the number, size and exact location of the defect. Any obstruction of the right ventricular outflow tract or insufficiency of the aortic valve can be identified. It can also provide a haemodynamic evaluation of the defect and estimate pulmonary artery pressure using the modified Bernoulli equation.

• In those with problems with image quality further information may be obtained using trans-oesophageal echocardiography.

• 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.

• Three-dimensional echocardiography may be used to estimate the size of VSDs more accurately as part of planning for surgical or catheter closure⁸ .
  

Cardiac catheterisation

• With advances in echocardiography, diagnostic cardiac catheterisation is used far less frequently than in the past. Apart from information about the location and number of defects, it can provide accurate measurement of pulmonary vascular resistance, pulmonary reactivity and volume of shunting.

Differential diagnosis

• Although VSD murmur is one of of the easier murmurs to recognise, sometimes an innocent physiological murmur can be mistaken for a VSD.

• Occasionally patent ductus arteriosus and pulmonary stenosis can be mistaken for a VSD.

Management¹

Medical management

• Management in the infant and child depends on symptoms, with small asymptomatic defects needing no medical management, and unlikely to need any intervention.

• First-line treatment for moderate or large defects affecting feeding and growth is with diuretics for heart failure and high-energy feeds to improve calorie intake.

• Angiotensin-converting enzyme inhibitors are used to reduce afterload which promotes direct systemic flow from the left ventricle, thus reducing the shunt. Digoxin can also be given for its inotropic effect.

• Any patient needing significant medical management should be referred for surgical assessment.

Surgical management

• Surgical repair is required if there is uncontrolled heart failure, including poor growth. Even very small babies may be considered for surgery.

• Infundibular defects may be considered for closure even if they are asymptomatic because of their location.

• Development of aortic valve prolapse and aortic regurgitation in perimembranous VSDs may be an indication for surgical closure.

• Most defects are closed nowadays by directly placing a patch from the right ventricular side, usually with the surgeon working through the tricuspid valve.

• Patients with large muscular VSDs which are difficult to see or those with multiple holes (Swiss cheese septum) presenting as neonates or infants need initial palliation in the form of pulmonary artery banding followed many months later by corrective surgery and removal of the pulmonary artery band.

Catheter closure

• Advances in catheter techniques and devices mean that many muscular and perimembranous VSDs can now be closed percutaneously. This is in the setting of normal atrioventricular and ventriculoarterial connections and absence of any atrioventricular or arterial valve override.

• Transcatheter techniques are useful because they avoid cardiopulmonary bypass. There are, however, recognised complications for device closure of perimembranous VSDs, including complete heart block needing permanent pacemaker⁹ .

• The National Institute for Health and Care Excellence (NICE) has provided detailed guidance on indications, efficacy and complications of the procedure¹⁰ .

• It is safer to close muscular VSDs using a device but muscular VSDs which are haemodynamically significant are likely to be seen in only young infants, making catheterisation difficult and challenging. Hybrid procedures increasingly being used involve insertion of the device in the operation theatre after surgical exposure of the defect¹¹ .

Endocarditis prophylaxis

• NICE guidelines (2008) do not recommend routine peri-procedure antibiotic prophylaxis against infective endocarditis in children or adults with congenital heart disease¹² .

Complications

• Perimembranous defects (especially the doubly committed type) can develop prolapse of aortic valve leaflets with eventual development of aortic regurgitation. Even small perimembranous defects are kept under regular cardiology follow-up.

• Some VSDs can be associated with development of muscular obstruction in the right or left ventricular outflow tract.

• Reversal of shunt with development of Eisenmenger's syndrome occasionally happens.

• Infective endocarditis is a lifelong risk in unoperated patients (18.7 per 10,000 patient-years) and in those with residual defects³ .

• Right bundle branch block may be caused by operative trauma, and occasionally complete heart block can occur. This has a late mortality.

Prognosis

• The prognosis for a patient with an isolated VSD is excellent.

• Spontaneous closure is common in children under 1 year old but less likely after the age of 2 years.

• Spontaneous closure in muscular VSD occurs with higher frequency and earlier than in perimembranous VSD. Approximately 80-90% of isolated muscular VSDs close spontaneously by 12 months of age¹³ .

• Subarterial infundibular VSDs do not close.

• In those needing surgery the surgical outcome is excellent and most units report a surgical mortality approaching zero.

• Prognosis is much worse in those with pulmonary hypertension or Eisenmenger physiology. These patients often have progressive exercise intolerance and worsening right ventricular function. They need specialised management including vasodilator therapy.

• As children with the perimembranous type grow older, the risk of aortic valve prolapse and regurgitation increases¹⁴ .

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-hour 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 consideration. Not all contraceptive methods can be safely used in adults with heart disease, and pregnancy may significantly increase cardiac risk in some types of heart disease. Specialist advice regarding contraception and pregnancy should be available to all adults with congenital heart disease and is best provided by cardiologists with a good understanding of their condition¹⁵ .

• Generally, small VSDs or operated VSDs do not pose additional cardiac risk with pregnancy and the risks associated with contraception are no higher than those of the general population.

• Maternal mortality is remarkably high (nearly 50%) in women with pulmonary hypertension of any cause. Pregnancy needs to be avoided in this group of patients as it may be life-threatening.

• Combined hormonal contraceptives are contra-indicated in women with pulmonary hypertension because of the thrombogenic effect of the oestrogen component. The progestogen-only pill (mini-pill) is safe but relatively ineffective and therefore not recommended. However, Cerazette® (prodrug of progesterone present in Implanon®) is a safe alternative with an efficacy similar to combined pills.

• Progestogen-only subdermal implants are almost as effective as sterilisation and recommended as long-acting reversible contraceptives.