Ventricular septal defect

These comprise around 30% of all cardiac defects. They vary from tiny defects, of pinhole size, to huge defects. Small defects are more common than large ones and are usually asymptomatic. Defects are frequently situated in the region of the membranous septum (perimembranous defects), but VSDs involving the muscular septum are also common (Fig. 15.2.1). Very tiny muscular defects may be demonstrated by echocardiography in infants with no clinical signs to suggest a septal defect.

Fig. 15.2.1 Sites of ventricular septal defect (VSD). In the left panel, the defect is close to the membranous part of the ventricular septum (perimembranous VSD). In the right panel, the defect is in the muscular septum. IVC, inferior vena cava; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle; SVC, superior vena cava.

Patent ductus arteriosus

Failure of the ductus arteriosus (which connects the pulmonary artery to the descending aorta) to close in the newborn period may be due to severe prematurity or to a congenital abnormality. The duct typically closes in the first few days of life. The clinical findings depend on the size of the duct and the amount of blood flow across the vessel. Patients with a small PDA are usually asymptomatic, with the only abnormality being a continuous murmur audible at the upper left sternal border or left infraclavicular area.

Such murmurs may be present throughout the cardiac cycle (‘machinery murmur’), but may disappear during diastole and be mistaken for a systolic murmur, especially if the duct is large and there is associated pulmonary hypertension.

With a large duct, the large left-to-right shunt causes left heart dilatation. Symptoms such as failure to thrive, dyspnoea and recurrent chest infections are similar to those of a large VSD. Bounding pulses may be palpable. The apex may be displaced and forceful, and an apical mid-diastolic murmur may be heard; as with a VSD, this is due to increased flow through the mitral valve.

The presence of cardiomegaly and pulmonary plethora on the chest X-ray indicates a large shunt, and left ventricular hypertrophy may be seen on the ECG. The diagnosis can be confirmed by echocardiography.

In symptomatic premature infants, medical treatment with indomethacin or other non-steroidal anti-inflammatory drugs, which inhibit prostaglandin synthesis, may be effective in promoting ductal constriction. Unfortunately, drug treatment is typically not effective in mature infants and in such patients intervention to close the ductus is indicated. This should be carried out at an early stage in symptomatic patients (including premature infants if indomethacin is ineffective) but may be delayed in asymptomatic patients. With small PDAs, intervention is indicated to eliminate the risk of infective endocarditis, rather than to treat cardiac failure or pulmonary hypertension. The risk of endocarditis occurring, however, is very small. The preferred method of duct occlusion is by a transcatheter approach. The type of device used depends on the size and shape of the PDA. Large ducts, especially those in small infants, may, however, require surgical ligation, typically from a left lateral thoractomy.

Atrial septal defect

Defects of the atrial septum are usually in the central part of the septum and are termed ‘secundum’ ASD (Fig. 15.2.2). Unlike small VSDs and PDAs (which tend to be associated with loud murmurs), small ASDs may go completely undetected because the volume of blood flow across the defect is small and also the pressure gradient across the defect, and hence the velocity of blood flow, are both low. With larger defects, a significant shunt is present, and this is rarely associated with pulmonary hypertension. Even large ASDs seldom cause symptoms in early childhood. If patients with large defects reach adult life without surgery, they may develop atrial arrhythmias in middle adult life and often have reduced exercise capacity, even if arrhythmias are not a problem. Isolated ASDs hardly ever lead to Eisenmenger syndrome.

Fig. 15.2.2 Common types of atrial septal defect (ASD). Secundum defects are in the fossa ovale (mid-atrial septum). Primum defects are low in the atrial septum and abut on the atrioventricular (AV) valves, which are abnormal and often incompetent. LA, left atrium; RA, right atrium.

The characteristic findings in children with an ASD are related to the increased blood flow through the right side of the heart and right heart enlargement. A parasternal heave related to a dilated right ventricle may be palpable. An ejection systolic murmur, due to increased pulmonary blood flow, is present in the pulmonary area but not usually louder than grade 2/6 and not harsh in character. A soft mid-diastolic murmur may be heard at the lower sternal border, secondary to increased flow across the tricuspid valve. The aortic and pulmonary components of the second heart sound are fixed and widely split (i.e. loss of the normal variation in separation during inspiration and expiration; see Fig. 15.1.2).

The chest X-ray characteristically shows cardiomegaly with pulmonary plethora. The ECG often shows features of partial right bundle branch block. The diagnosis may be confirmed by echocardiography.

Closure of the defect is recommended in patients where there is evidence of a significant shunt as indicated by right heart enlargement. In many cases a transcatheter procedure can be performed with placement of an ‘occluder’ device. This is a non-surgical option for patients with central defects of small to moderate size with good margins that are able to support the device without interfering with surrounding structures such as the mitral valve, right-sided pulmonary veins or the vena cavae. Surgical repair either by direct suture or patch closure may be required for defects that are unsuitable for a transcatheter approach.

Atrioventricular septal defect

This category of defect accounts for approximately 3% of all congenital cardiac defects and includes a group of septal defects low in the atrial septum (primum ASD) that abut on the atrioventricular valves and may involve the upper part of the ventricular septum.

When the ventricular septum is intact (partial AVSD or primum ASD), only an atrial communication is present. In addition to the septal defect, the atrioventricular junction and valves are abnormal in all forms of AVSD. The left-sided atrioventricular valve in this condition typically has three leaflets rather than the usual two-leaflet mitral valve. This is sometimes described incorrectly as a cleft in the mitral valve and is associated with varying degrees of regurgitation. Children with a primum ASD or partial AVSD behave physiologically and symptomatically like those with an ASD. Those with significant regurgitation of the left-sided atrioventricular valve, however, develop symptoms much earlier in infancy and early childhood.

When a significant VSD coexists (complete AVSD; Fig. 15.2.3), the presentation resembles that of a VSD with difficulty feeding and failure to thrive. This defect is commonly associated with Down syndrome.

Fig. 15.2.3 Atrioventricular (AV) septal defect. The complete form is associated with a common AV valve and the septal defect allows communication between all four cardiac chambers. ASD, atrial septal defect.

The chest X-ray usually shows quite marked cardiomegaly and pulmonary plethora, especially in the complete form of the defect. The ECG characteristically shows left-axis deviation accompanied by partial right bundle branch block. The presence of left-axis deviation distinguishes ‘primum’ ASDs from ‘secundum’ defects. Echocardiography confirms the diagnosis and will differentiate partial from complete atrioventricular defects.

Surgical repair is almost always required. When pulmonary hypertension is present, this is generally recommended in the early months of life (3–4 months) in order to obviate the risk of pulmonary vascular disease, particularly in children with Down syndrome. In patients with an isolated primum ASD, when pulmonary hypertension is absent, surgery may be delayed until the age of 2–4 years. Operation involves placement of a patch to close the ASD and repair of the left atrioventricular valve. Although there is an association with both types of AVSD, left ventricular outflow tract obstruction is more likely to occur with partial than complete AVSDs.

Pulmonary stenosis

Pulmonary stenosis usually occurs at valve level and is the commonest of the pure obstructive malformations. The pulmonary valve often has thickened leaflets and partially fused commissures. In some cases the valve may be bicuspid. Other sites of pulmonary stenosis, occurring as isolated abnormalities, are less frequent. These include muscular subpulmonary obstruction involving the right ventricular outflow tract (infundibular stenosis) and supravalvular or branch pulmonary stenosis.

Most patients are asymptomatic in infancy and childhood because very severe (‘critical’) obstruction is uncommon and even moderate obstruction is generally well tolerated. An ejection systolic murmur is heard at the left upper sternal edge and radiates through to the back. An early ejection sound (ejection click) is usually audible at the left sternal border (Fig. 15.2.4) with valvar stenosis.

Fig. 15.2.4 Auscultatory findings in pulmonary and aortic stenosis. The ejection click (EC) is earlier in pulmonary stenosis and the second sound is widely split. In aortic stenosis the click is best heard at the apex.

The size of the heart is usually normal on chest X-ray, but the main pulmonary artery is often prominent due to post-stenotic dilatation. The ECG is normal with mild obstruction but shows right ventricular hypertrophy in more severe cases.

Mild pulmonary stenosis is generally a benign condition and is often non-progressive. More severe pulmonary stenosis leads eventually to effort intolerance and cardiac failure. ‘Critical’ (very severe) pulmonary stenosis may present in early infancy with cyanosis due to right-to-left shunting through the foramen ovale or an associated ASD.

The diagnosis may be confirmed by echocardiography. Treatment involves a catheter technique known as balloon valvuloplasty. This involves manipulating a catheter-mounted balloon to lie across the pulmonary valve, typically using the femoral vein for access, and then inflating the balloon to open the valve more fully. This procedure is simple and effective in most cases, requires only a very short hospital stay and saves the patient an open heart operation. If this is not effective, as is often the case when the valve leaflets are very thickened or the valve annulus is small, surgical valvotomy may need to be performed. Balloon valvuloplasty is not used for subpulmonary obstruction and is rarely effective in supravalve stenosis.

Aortic stenosis

Valve stenosis with thickened, often bicuspid, leaflets and fused commissures is the most common form of aortic stenosis. Subaortic stenosis due to either a fibrous stricture or muscular obstruction in the left ventricular outflow tract, or supra-aortic stenosis (i.e. above the aortic valve) are less common causes of left heart obstruction.

Except in very severe cases, affected children are symptom-free in infancy and early childhood, and present with the chance finding of an ejection systolic murmur over the precordium and in the aortic area. Characteristically, with valvar stenosis the murmur is best heard to the right of the sternum and radiates to the carotids. A thrill is commonly present over the carotids and may also be felt in the aortic area. An ejection click is usually heard with valvar stenosis (see Fig. 15.2.4) and is often most easily audible at the apex or lower left sternal border. In more severe cases a forceful apical impulse due to left ventricular hypertrophy may be apparent. In subaortic stenosis the murmur is best heard at the left sternal edge and a click is not heard. Conversely, the murmur of supravalvar stenosis is often best heard over the carotid artery.

The natural history of aortic stenosis is generally one of gradual progression. With more severe obstruction, symptoms include dizziness and syncope on exertion, chest pain, effort intolerance and sudden death. In a small minority of cases, with ‘critical’ stenosis, severe congestive heart failure may appear in early infancy.

In mild and even moderate aortic stenosis, the chest X-ray and ECG may show little abnormality. In more severe cases the ECG shows left ventricular hypertrophy. Echocardiography allows assessment of the site and severity of the obstruction.

Treatment should be recommended if severe stenosis is present, even in the absence of symptoms. In cases of moderate stenosis the presence of symptoms as described above or ECG changes on exercise are an indication for treatment. Balloon aortic valvuloplasty is an alternative to surgery, but is more likely to induce aortic regurgitation. Surgical repair involves aortic valvotomy using cardiopulmonary bypass.