Cardiac disorders
Recent developments in paediatric cardiac disease are:
• Lesions are being increasingly identified on antenatal ultrasound screening
• Most lesions are diagnosed by echocardiography, the mainstay of diagnostic imaging
• MRI allows three-dimensional reconstruction of complex cardiac disorders, assessment of haemodynamics and flow patterns and assists interventional cardiology, reducing the need for cardiac catheterisation
• Most defects can be corrected by definitive surgery at the initial operation
• An increasing number of defects (60%) are treated non-invasively, e.g. persistent ductus arteriosus
• New therapies are available to treat pulmonary hypertension and delay transplantation
• The overall infant cardiac surgical mortality has been reduced from approximately 20% in 1970 to 2% in 2010.
Epidemiology
Heart disease in children is mostly congenital. It is the most common single group of structural malformations in infants:
• 8 per 1000 liveborn infants have significant cardiac malformations
• Some abnormality of the cardiovascular system, e.g. a bicuspid aortic valve, is present in 1–2% of live births
The nine most common anomalies account for 80% of all lesions (Box 17.1), but:
Aetiology
Genetic causes are increasingly recognised in the aetiology of congenital heart disease, now in more than 10%. These might affect whole chromosomes, point mutations or microdeletions (Table 17.1). Polygenic abnormalities probably explain why having a child with congenital heart disease doubles the risk for subsequent children and the risk is higher still if either parent has congenital heart disease. A small proportion are related to external teratogens.
Table 17.1
Causes of congenital heart disease
| Cardiac abnormalities | Frequency | |
| Maternal disorders | ||
| Rubella infection | Peripheral pulmonary stenosis, PDA | 30–35% |
| Systemic lupus erythematosus (SLE) | Complete heart block (anti-Ro and anti-La antibody) | 35% |
| Diabetes mellitus | Incidence increased overall | 2% |
| Maternal drugs | ||
| Warfarin therapy | Pulmonary valve stenosis, PDA | 5% |
| Fetal alcohol syndrome | ASD, VSD, tetralogy of Fallot | 25% |
| Chromosomal abnormality | ||
| Down syndrome (trisomy 21) | Atrioventricular septal defect, VSD | 30% |
| Edwards syndrome (trisomy 18) | Complex | 60–80% |
| Patau syndrome (trisomy 13) | Complex | 70% |
| Turner syndrome (45XO) | Aortic valve stenosis, coarctation of the aorta | 15% |
| Chromosome 22q11.2 deletion | Aortic arch anomalies, tetralogy of Fallot, common arterial trunk | 80% |
| Williams syndrome (7q11.23 microdeletion) | Supravalvular aortic stenosis, peripheral pulmonary artery stenosis | 85% |
| Noonan syndrome (PTPN11 mutation and others) | Hypertrophic cardiomyopathy, atrial septal defect, pulmonary valve stenosis | 50% |
ASD, atrial septal defect; PDA, persistent ductus arteriosus; VSD, ventricular septal defect.
Circulatory changes at birth
In the fetus, the left atrial pressure is low, as relatively little blood returns from the lungs. The pressure in the right atrium is higher than in the left, as it receives all the systemic venous return including blood from the placenta. The flap valve of the foramen ovale is held open, blood flows across the atrial septum into the left atrium and then into the left ventricle, which in turn pumps it to the upper body (Fig. 17.1).
With the first breaths, resistance to pulmonary blood flow falls and the volume of blood flowing through the lungs increases six-fold. This results in a rise in the left atrial pressure. Meanwhile, the volume of blood returning to the right atrium falls as the placenta is excluded from the circulation. The change in the pressure difference causes the flap valve of the foramen ovale to be closed. The ductus arteriosus, which connects the pulmonary artery to the aorta in fetal life, will normally close within the first few hours or days. Some babies with congenital heart lesions rely on blood flow through the duct (duct-dependent circulation). Their clinical condition will deteriorate dramatically when the duct closes, which is usually at 1–2 days of age but occasionally later.
Presentation
Congenital heart disease presents with:
Antenatal diagnosis
Checking the anatomy of the fetal heart has become a routine part of the fetal anomaly scan performed in developed countries between 18 and 20 weeks’ gestation and can lead to 70% of those infants who require surgery in the first 6 months of life being diagnosed antenatally. If an abnormality is detected, detailed fetal echocardiography is performed by a paediatric cardiologist. Any fetus at increased risk, e.g. suspected Down syndrome, where the parents have had a previous child with heart disease or where the mother has congenital heart disease, is also checked. Early diagnosis allows the parents to be counselled. Depending on the diagnosis, some choose termination of pregnancy; the majority continue with the pregnancy and can have their child’s management planned antenatally. Mothers of infants with duct-dependent lesions likely to need treatment within the first 2 days of life may be offered delivery at or close to the cardiac centre.
Heart murmurs
The most common presentation of congenital heart disease is with a heart murmur. Even so, the vast majority of children with murmurs have a normal heart. They have an ‘innocent murmur’, which can be heard at some time in almost 30% of children. It is obviously important to be able to distinguish an innocent murmur from a pathological one.
Hallmarks of an innocent ejection murmur are (all have an ‘S’, ‘innoSent’):
During a febrile illness or anaemia, innocent or flow murmurs are often heard because of increased cardiac output. Therefore it is important to examine the child when such other illnesses have been corrected.
Differentiating between innocent and pathological murmurs can be difficult. If a murmur is thought to be significant, or if there is uncertainty about whether it is innocent, the child should be seen by an experienced paediatrician to decide about referral to a paediatric cardiologist for echocardiography. A chest radiograph and ECG may help with the diagnosis beyond the neonatal period.
Many newborn infants with potential shunts have neither symptoms nor a murmur at birth, as the pulmonary vascular resistance is still high. Therefore, conditions such as a ventricular septal defect or ductus arteriosus may only become apparent at several weeks of age when the pulmonary vascular resistance falls.
The features of an innocent murmur can be remembered as the five Ss:
‘InnoSent’ murmur = Soft, Systolic, aSymptomatic, left Sternal edge.
Heart failure
Signs
Signs of right heart failure (ankle oedema, sacral oedema and ascites) are rare in developed countries, but may be seen with long-standing rheumatic fever or pulmonary hypertension, with tricuspid regurgitation and right atrial dilatation.
In the first week of life, heart failure (Box 17.2) usually results from left heart obstruction, e.g. coarctation of the aorta. If the obstructive lesion is very severe then arterial perfusion may be predominantly by right-to-left flow of blood via the arterial duct, so-called duct-dependent systemic circulation (Fig. 17.2). Closure of the duct under these circumstances rapidly leads to severe acidosis, collapse and death unless ductal patency is restored (Case History 17.1).
After the first week of life, progressive heart failure is most likely due to a left-to-right shunt (Case History 17.2). During the subsequent weeks, as the pulmonary vascular resistance falls, there is a progressive increase in left-to-right shunt and increasing pulmonary blood flow. This causes pulmonary oedema and breathlessness.
Such symptoms of heart failure will increase up to the age of about 3 months, but may subsequently improve as the pulmonary vascular resistance rises in response to the left-to-right shunt. If left untreated, these children will develop Eisenmenger syndrome, which is irreversibly raised pulmonary vascular resistance resulting from chronically raised pulmonary arterial pressure and flow. Now the shunt is from right to left and the teenager is blue. If this develops, the only surgical option is a heart-lung transplant, if available, although medication is now available to palliate the symptoms.
Cyanosis
• Peripheral cyanosis (blueness of the hands and feet) may occur when a child is cold or unwell from any cause or with polycythaemia
• Central cyanosis, seen on the tongue as a slate blue colour, is associated with a fall in arterial blood oxygen tension. It can only be recognised clinically if the concentration of reduced haemoglobin in the blood exceeds 5 g/dl, so it is less pronounced if the child is anaemic
• Check with a pulse oximeter that an infant’s oxygen saturation is normal (≥94%). Persistent cyanosis in an otherwise well infant is nearly always a sign of structural heart disease.
Cyanosis in a newborn infant with respiratory distress (respiratory rate >60 breaths/min) may be due to:
• Cardiac disorders – cyanotic congenital heart disease
• Respiratory disorders, e.g. surfactant deficiency, meconium aspiration, pulmonary hypoplasia, etc.
• Persistent pulmonary hypertension of the newborn (PPHN) – failure of the pulmonary vascular resistance to fall after birth
• Infection – septicaemia from group B streptococcus and other organisms
Case History
A 2-day-old baby had been discharged home the day after delivery following a normal routine examination. He suddenly collapsed and was rushed to hospital. He was pale, with grey lips. The right brachial pulse could just be felt, the femoral pulses were impalpable and his liver was significantly enlarged. Blood gases showed a severe metabolic acidosis. The differential diagnosis was:
He was ventilated and treated with volume support. Blood cultures were taken and antibiotics started for possible sepsis. Blood and urine samples were taken for an amino acid screen and urine for organic acids. As the femoral pulses remained impalpable, a prostaglandin infusion was started. Within 2 hours, he was pink and well perfused and the acidosis was resolving. Severe coarctation of the aorta (Fig. 17.3) was diagnosed on echocardiography. He had developed shock from a left heart outflow tract obstruction once the arterial duct had closed.
Case History
A 5-week-old female infant was referred to hospital because of wheezing, poor feeding and poor weight gain during the previous 2 weeks. Before this, she had been well. Her routine neonatal examination had been normal. She was tachypnoeic (50–60 breaths/min) and there was some sternal and intercostal recession. The pulses were normal. There was a thrill, a pansystolic murmur at the lower left sternal edge and a slightly accentuated pulmonary component to the second heart sound. There were scattered wheezes. The liver was enlarged, palpable at two fingerbreadths below the costal margin. The ECG was unremarkable. The chest radiograph showed cardiomegaly and increased pulmonary vascular markings. An echocardiogram showed a moderate-sized ventricular septal defect (VSD) (Fig. 17.4). Treatment was medical with diuretics and captopril. The VSD closed spontaneously at 18 months.
This infant developed heart failure from a moderate VSD presenting at several weeks of age when the pulmonary resistance fell, causing increased left-to-right shunting of blood. The defect closed spontaneously.
Whether the presentation of congenital heart disease is with a heart murmur, heart failure, cyanosis or shock depends on the underlying anatomic lesion causing:
This is summarised in Table 17.2.
Table 17.2
Types of presentation with congenital heart disease
| Type of lesion | Left-to-right shunt | Right-to-left shunt | Common mixing | Well children with obstruction | Sick neonates with obstruction |
| Symptoms | Breathless or asymptomatic | Blue | Breathless and blue | Asymptomatic | Collapsed with shock |
| Examples | ASD | Tetralogy of Fallot | AVSD | AS | Coarctation |
| VSD | TGA | Complex congenital heart disease | PS | HLHS | |
| PDA | Adult-type CoA |
ASD, atrial septal defect; VSD, ventricular septal defect; PDA, patent ductus arteriosus; TGA, transposition of the great arteries; AVSD, atrioventricular; AS, aortic stenosis; PS, pulmonary stenosis; CoA, coarctation of the aorta; HLHS, hypoplastic left heart syndrome.
Diagnosis
If congenital heart disease is suspected, a chest radiograph and ECG (Box 17.3) should be performed. Although rarely diagnostic, they may be helpful in establishing that there is an abnormality of the cardiovascular system and as a baseline for assessing future changes. Echocardiography, combined with Doppler ultrasound, enables almost all causes of congenital heart disease to be diagnosed. Even when a paediatric cardiologist is not available locally a specialist echocardiography opinion may be available via telemedicine, or else transfer to the cardiac centre will be necessary. A specialist opinion is required if the child is haemodynamically unstable, if there is heart failure, if there is cyanosis, when the oxygen saturations are <94% due to heart disease and when there are reduced volume pulses.
Nomenclature
The European (as opposed to American) system for naming congenital heart disease is referred to as sequential segmental arrangement. The advantage is that it is not necessary to remember the pattern of an eponymous syndrome, e.g. tetralogy of Fallot. The disadvantage is that it is longwinded. The idea is that each component is described in turn, naming the way the atria, then the ventricles and then the great arteries are connected. Hence, a normal heart will be described as situs solitus (i.e. the atria are in the correct orientation), concordant atrioventricular connection and concordant ventriculo–arterial connection. Therefore a heart of any complexity can be described in a logical step-by-step process. This system is not described here, as it is beyond the scope of this book.
Left-to-right shunts
Atrial septal defect
There are two main types of atrial septal defect (ASD):
• Secundum ASD (80% of ASDs) (Fig. 17.5a)
• Partial atrioventricular septal defect (primum ASD, pAVSD) (Fig 17.5b).
Partial AVSD is a defect of the atrioventricular septum and is characterised by:
• An inter-atrial communication between the bottom end of the atrial septum and the atrioventricular valves (primum ASD)
• Abnormal atrioventricular valves, with a left atrioventricular valve which has three leaflets and tends to leak (regurgitant valve).
Clinical features
Physical signs (Fig. 17.5c)
• An ejection systolic murmur best heard at the upper left sternal edge – due to increased flow across the pulmonary valve because of the left-to-right shunt
• A fixed and widely split second heart sound (often difficult to hear) – due to the right ventricular stroke volume being equal in both inspiration and expiration
• With a partial AVSD, an apical pansystolic murmur from atrioventricular valve regurgitation.
Atrial septal defect
Investigations
ECG
• Secundum ASD – partial right bundle branch block is common (but may occur in normal children), right axis deviation due to right ventricular enlargement (Fig. 17.5e)
• Partial AVSD – a ‘superior’ QRS axis (mainly negative in AVF) (Fig 17.5f). This occurs because there is a defect of the middle part of the heart where the atrioventricular node is. The displaced node then conducts to the ventricles superiorly, giving the abnormal axis.
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