Fetal circulatory pathways

The fetal circulation consists of parallel systemic and pulmonary pathways in contrast to the normal postnatal circulation, in which the systemic and pulmonary circulations exist in series ( Fig. 28.1 ). For the most part, prenatal survival is possible with even major structural cardiovascular malformations, provided that either the right or left ventricle is able to pump blood derived from the great veins into the fetal aorta. It is this remarkably adaptive nature of the fetal circulation which enables fetuses with complex malformations such as those with atresia of either of the semilunar valves to survive throughout pregnancy. In the fetus, oxygenated blood returns from the placenta via the umbilical vein into the inferior caval vein, either through the portal system or through the venous duct. The proportion of blood channelled through these different routes changes as pregnancy progresses and will adapt continuously to the metabolic demands of the fetus by flow regulation in the venous duct. The stream of inferior caval blood entering the right atrium is divided as it hits the superior rim of the oval foramen and the majority of the blood enters the left atrium through the foramen. As pregnancy advances, the proportion crossing into the left atrium falls. Superior caval vein blood enters the right atrium and the majority will enter into the right ventricle via the tricuspid valve. Almost all of the right ventricular (RV) output will be directed through the arterial duct into the systemic circulation, bypassing the high-resistance pulmonary circulation. The proportion of pulmonary blood flow also changes with gestation, increasing during the third trimester. Just as in postnatal life, the fetal pulmonary vascular bed is reactive. Fetal pulmonary blood flow can be increased by manipulation of the pulmonary vasculature bed with pulmonary vasodilator agents (such as oxygen) administered to the mother (Rasanen et al. 1998). As pregnancy progresses, the effective cardiac output increases to a maximum of approximately 250 ml/kg/min by term, with the right ventricle contributing 55% and the left ventricle 45% of the fetal cardiac output. Of the combined output, 65% returns to the placenta and 35% to the fetal organs and tissues ( ).

Schematic representation of the fetal circulatory pathways. The placenta is drawn to a greatly reduced scale.

( Reproduced with permission from Gray’s Anatomy, 40th ed. Elsevier Inc. Fig 59.17.)

Function of the fetal heart

Compared with the normal adult heart, there are a number of differences both within the fetal heart itself as well as between the physiological environment during fetal and postnatal life which explain many of the observations of fetal cardiac function. In early fetal life, the expression of contractile proteins is different from the postnatal pattern ( ). In addition, the expression of different types of collagen within fetal heart muscle results in reduced compliance of the fetal heart compared with the postnatal heart ( ). With advancing gestation, there is continuing maturation of excitation–contraction coupling as well as increasing autonomic innervation ( ). As a result, the immature fetal heart is much less compliant and less able to generate contractile force than its adult counterpart, for the same degree of stretch. However, the observation that the Starling curve in the fetus is blunted should not be attributed to the differences in the fetal myocardium alone. It is significantly influenced by the external constraints existing around the heart in the fetus, including the fluid-filled lungs and rigid chest wall.

Changes at birth

The most dramatic events that occur with birth are a shift from a circulation in parallel to one in series, as well as a marked increase in cardiac output from both ventricles. At term, the cardiac output from each ventricle approximately equals the combined cardiac output from both ventricles in the immediately preterm fetus. With inspiration, there is a rapid fall in pulmonary vascular resistance (PVR), as lung expansion allows new vessels to open and existing vessels to enlarge. Reduced resistance and decreased pulmonary artery pressures increase pulmonary blood flow. Simultaneously, the lower resistance placental circulation is removed from the systemic circulation as the cord is cut. The increased preload occurring from placental return can now be converted into useful increased cardiac output, once the external constraints of fluid-filled lungs around the heart are replaced by more compliant air-filled lungs. The sudden increase in oxygen tension produced by breathing alters local prostaglandin synthesis, resulting in a constriction of both the arterial and venous ducts. For most neonates, functional closure of the arterial duct will have occurred within 24–72 hours and anatomical closure is complete within 1–2 weeks. The oval foramen and venous duct may remain patent for some time after birth, with the potential to allow shunting. This can mask the signs of underlying structural congenital cardiovascular malformations, such as infracardiac total anomalous pulmonary venous drainage or, occasionally, transposition of the great arteries (TGA). The oval foramen is functionally closed in the majority of cases by the third month of life. Continued patency may contribute to clinical problems in some conditions ( Table 28.1 ).

Diagnosis

Fetal cardiac anatomy, function and rhythm have been determined by transabdominal scanning from 18 weeks’ gestation for the last two decades ( ). An approach using both abdominal and (when necessary) transvaginal scanning in high-risk cases at 10–13 weeks allowed interpretable images in over 80% of cases ( ), with a probable low false-positive rate, although verification was incomplete. Screening fetal cardiac anatomy with a four-chamber view at 18 weeks is a routine part of the general anomaly scan, but this will pick up under 50% of cases of structural heart lesions, even in experienced hands ( ; ). Heart lesions picked up by a four-chamber screening scan are generally the more complex ones with a poorer outlook both prenatally and after delivery. If views of the outflow tracts are obtained in addition to the four-chamber view, the range of abnormalities detectable is increased ( ). In particular, transposition, tetralogy of Fallot and similar lesions should be detected.

Detailed evaluation of fetal cardiac anatomy by ultrasound is much more time-consuming and is usually reserved for women with an increased risk of having a fetus with a cardiac problem ( Table 28.2 ). However, when detailed echocardiography was used on all pregnancies, reported 86% sensitivity and 100% specificity. The conditions missed were mainly atrial septal defects (ASDs) and small ventricular septal defects (VSDs). Other workers have pointed out the difficulty in diagnosing coarctation and total anomalous pulmonary venous connection (TAPVC) in the fetus ( ). Abnormalities of fetal heart rhythm can be determined by M-mode and Doppler studies.

There are ethical aspects to fetal diagnosis and practitioners in this field need to be sensitive to parental views. Fetal cardiac scanning should be carried out in the context of expertise in all aspects of fetal medicine, including the provision of support to families. The association with non-cardiac abnormalities is strong and these are often major influences in the natural history in utero and after birth, as well as in decisions about continuation of pregnancy. For example, in one study in which cardiac scans were performed for a variety of indications, 70% of fetuses with a cardiac anomaly had an underlying chromosome abnormality ( ).

Treatment

Accurate diagnosis of structural heart disease in a fetus allows information to be given to families and provides for greater choice. Some parents will opt for termination of pregnancy and about 5% of fetuses with structural cardiac abnormalities will die in utero ( ). Cardiac diagnosis and prognosis must be considered in the context of full fetal assessment, as non-cardiac abnormalities may well be more important in determining the overall prognosis. The combination of a structural cardiac abnormality and an extracardiac abnormality will often influence outcome more adversely than anticipated for either lesion alone.

In pregnancies progressing to viability, a cardiac diagnosis will, in a minority of cases, influence place, time or mode of delivery, but non-cardiac factors also need to be taken into account. The most important point with respect to early postnatal management of heart disease is whether or not the lesion is likely to be duct-dependent, thereby allowing prostaglandin to be used before symptoms develop. Progressive underdevelopment of the ventricle in the fetus with severe arterial valve stenosis is well recognised ( ; ) and prenatal arterial valve balloon valvuloplasty has been performed with limited proven efficacy ( ; ). Some structural lesions do not progress with advancing gestation and, in those that do, only a tiny minority are suitable for any form of prenatal intervention. There is evidence that fetal diagnosis of severe duct-dependent congenital heart disease (CHD) results in babies reaching a cardiac centre in better condition than those not diagnosed until after delivery ( ). Benefit from fetal diagnosis in terms of improved survival and morbidity has been shown for coarctation ( ), and in improved mortality in transposition ( ) and hypoplastic left heart ( ), although, in the last two conditions, the benefit from prenatal diagnosis has been difficult to demonstrate ( ). Reassurance of normality or the chance to prepare for the arrival of an abnormal baby is valued by many parents but has not been formally quantified.

Accurate diagnosis of fetal dysrhythmias is essential to avoid unnecessary intervention and to allow appropriate treatment which can almost always improve the outlook for the fetus with a haemodynamically compromising rhythm disturbance. Diagnosis and management of abnormal fetal rhythms are discussed in the section on neonatal rhythm disturbances ( p. 661 ).

Normal adaptation

Normal adaptation of the fetal circulation at birth may have adverse haemodynamic effects in some congenital cardiac malformations just as failure of normal changes to occur may be disadvantageous under certain circumstances.

Ductus venosus

Closure of the ductus venosus is of importance in that it removes the possibility of central venous access being obtained via the umbilical vein for monitoring, balloon septostomy or cardiac catheterisation. It will also result in marked deterioration in cases of TAPVC to the portal vein as it will cause severe pulmonary venous obstruction with pulmonary congestion ( Fig. 28.2 ). In this condition, closure of the ductus venosus may not occur until some days after birth. Delay in or failure of closure of the ductus venosus is probably rare and never of significance.

(A) Anteroposterior chest X-ray in a neonate with obstructed total anomalous pulmonary venous connection showing pulmonary venous congestion and normal heart size. (B) Volume-rendered three-dimensional magnetic resonance imaging reconstruction in the same patient viewed from behind showing four pulmonary veins entering into a vertical confluence behind the left atrium, which is drained by a large descending vein entering into the hepatic venous system. The descending vein is narrowed as it crosses the diaphragm and the hepatic veins, with which it communicates, are dilated.

Dysmorphic features and non-cardiac malformations

These must be carefully sought and described in detail in relation to all body systems. They are clearly important if a syndrome is to be diagnosed and may influence treatment plans and prognostic information given to families. It may be relevant to investigate other systems on the basis of certain cardiac diagnoses, for example chromosome analysis or immunological assessment. In some circumstances, recognition of an abnormality in an infant will result in a diagnosis being made in a parent, for example 22q11 deletion or Noonan syndrome. When certain non-cardiac structural abnormalities are recognised, a detailed cardiac evaluation is appropriate, as in Down syndrome and many gastrointestinal abnormalities ( ). Of all children with chromosomal abnormalities, at least 30% have a congenital cardiac defect ( ).

Pulses

Impalpable or weak femoral pulses in the presence of good-volume upper limb pulses suggest coarctation of the aorta, in which case other signs may well be present and might include upper limb hypertension, systolic pressure difference between arms and legs, evidence of aortic valve abnormality (ejection click), a bruit between the scapulae and signs of heart failure. If all pulses are weak, then left ventricular outflow obstruction, hypovolaemia or left ventricular dysfunction should be considered. Hypoplastic left heart may be associated with stronger femoral than right brachial pulses before the DA closes. A preterm infant severely compromised by PDA may have very weak femoral pulses. A baby with interrupted aortic arch usually collapses in the first week of life; the diagnosis and the site of interruption can sometimes be deduced by comparing arm and neck pulses as they will be much stronger proximal to the interruption.

Blood pressure

Blood pressure (BP) should be measured in both arms and in one leg in any newborn infant with cardiac symptoms and in an asymptomatic infant if other signs raise the possibility of coarctation. A difference in systolic BP of 20 mmHg or more between arm and leg is strongly suggestive of coarctation, although smaller gradients in term babies can be normal and the absence of such a difference may not rule out the diagnosis of coarctation if the DA is still patent. BP should also be measured in any unwell baby, as well as in those with urinary tract abnormalities, those on steroids, in CLD and in the infants of drug-addicted mothers. It is essential that the baby is settled; results on crying babies are misleading. Monitoring BP is part of the management of severely ill babies and this should be carried out invasively wherever possible. Obtaining a definitive non-invasive BP requires patience and attention to detail. The arterial pulse can be detected by palpation or with a Doppler probe. Both methods will only give a systolic value. Auscultation is very difficult and the flush method is rarely used. Oscillometric monitors may be useful in sequential BP monitoring of immobile babies but even then are subject to error at low pressures in infants with extremely low birthweight. Cuff size is important and for the arm it should cover 75% of the distance from axilla to elbow or have a width that is 40–50% of the arm circumference ( ). The bladder should virtually encircle the arm. Leg BP can be measured using the same cuff around the calf with detection of a dorsalis pedis or posterior tibial pulse. Normal BP values are given in Appendix 4 .

Cyanosis

Peripheral cyanosis is very common in normal newborn babies. Central cyanosis in the presence of structural cardiac disease is caused by three main mechanisms, which may coexist. The commonest is obstruction to pulmonary blood flow with a right-to-left shunt. Cyanosis is also evident when there are discordant ventriculoarterial connections (as in transposition) with adverse streaming of blood within the heart. Thirdly, cyanosis will also occur where there is common mixing of blood, which can occur at atrial, ventricular or great artery level, allowing the mixed systemic and pulmonary venous return to be distributed to both the aorta and the pulmonary arteries.

Central cyanosis in the neonate may have a respiratory cause but can also be mimicked by facial petechiae (traumatic cyanosis) and can be seen in markedly polycythaemic infants. Plethoric infants with a low normal oxygen saturation may have enough deoxygenated haemoglobin to give true central cyanosis. Pigmentation of the lips can also confuse the observer and it is important to look at the tongue to get the best possible assessment of saturation. Anaemia and desaturation make a baby look pale grey rather than really blue, and methaemoglobinaemia gives babies a slate black or grey colour which is often mistaken for cyanosis. Cyanotic, often termed ‘dusky’, episodes are very common and are only occasionally a presenting feature for structural heart disease; persistent cyanosis is far more likely to be cardiac, although it may vary in intensity. Cyanosis whilst crying is rarely pathological if colour and behaviour return to normal rapidly when the infant stops crying. Hypercyanotic episodes, as seen in tetralogy of Fallot and related conditions, are rare in the newborn period.

Heart failure

Fetal echo has shown that prenatal cardiac failure can be caused by myocardial dysfunction, structural abnormalities and arrhythmias. In newborns, early heart failure usually results from myocardial dysfunction, left-heart obstructive lesions, tachyarrhythmias and large arteriovenous malformations (AVMs). These result in tachycardia, tachypnoea with recession, liver enlargement and cardiomegaly. These conditions are a medical emergency. With advancing age, lesions that cause a large left-to-right shunt are the most frequent cause of heart failure (large VSD or big PDA). They manifest as PVR falls and signs appear more quickly when there are combinations of lesions. The signs of heart failure in the older neonate are subtly different, with poor feeding, slow weight gain and tachypnoea being the most common. Common features of neonatal heart failure are listed in Table 28.6 .

Heart murmur

Heart murmurs in the newborn are common, occurring in up to 0.6% of newborns ( ). They may be associated with both major and minor cardiac lesions but also can be a normal physiological finding. Many serious cardiac conditions have unimpressive or even no murmurs in the newborn period. Other auscultatory and general cardiovascular signs are therefore very important in assessing the significance of a murmur. The absence of any other features of cardiac disease as well as the presence of certain positive murmur characteristics are required to diagnose innocent heart murmurs. The typical heart murmur in newborn babies comes from the pulmonary artery branches and disappears before 6 months of age in term infants. In practice, cardiac murmurs in the newborn that are associated with additional cardiac symptoms or signs justify prompt echocardiographic assessment unless the diagnosis has been documented prenatally, in which case knowledge of the diagnosis and clinical assessment should determine the timing of investigation. Asymptomatic murmurs will almost always need formal investigation with echocardiography but this can usually be undertaken on an elective basis.

Airway obstruction

This uncommon presentation is usually associated with inspiratory stridor. When associated with a structural cardiac abnormality, the manifestations are usually caused by a vascular ring such as a pulmonary artery sling or a double aortic arch. Major airway obstruction can occur as part of the absent pulmonary valve syndrome in association with tetralogy of Fallot.

Chest radiography

CXR is less valuable in the newborn period in the evaluation of CHD because the appearance can be normal even in the presence of a severe congenital cardiac malformation. Its value lies in its availability, cost and the additional information it provides. Visceral situs, cardiac position, cardiac size and bony abnormalities of the chest are all well seen on the CXR. Features to look for in this context are listed in Table 28.7 ; examples are shown in Figures 28.3–28.6 and see Ch. 43 . The role of the CXR has diminished with the more widespread use of transthoracic echocardiography.

Posteroanterior chest X-ray showing marked cardiomegaly with pulmonary plethora in association with congestive cardiac failure.

Posteroanterior chest X-ray showing normal abdominal situs with dextrocardia.

Posteroanterior chest X-ray showing abdominal situs inversus with a midline liver and dextrocardia.

Posteroanterior chest X-ray showing massive cardiomegaly in a neonate with severe Ebstein’s anomaly.

Electrocardiogram

The ECG provides useful information in a number of areas ( Table 28.8 ), providing attention is paid to technical aspects of obtaining a good recording, which can be difficult in a neonatal nursery. Systematic reading of the ECG will optimise the information obtained and reference should be made to normal values ( Appendix 3 ) and to a standard text for detailed interpretation of ECGs ( ).

QRS axis

The frontal QRS axis can be calculated as shown in Figure 28.9 . An abnormal QRS axis may be an important diagnostic clue in a number of conditions, including AVSD ( Fig. 28.10 ) and tricuspid atresia (QRS usually −30°); in the former case it makes the ECG a valuable screening investigation in newborn infants with Down syndrome, in whom clinical features of AVSD may be absent or very subtle.

Electrocardiogram standard leads, superior QRS axis (−90°), newborn with complete atrioventricular septal defect.

Hexaxial reference system for calculating the frontal plane axis of the QRS complex (and of P and T waves if required). The frontal axis of the QRS complex can be estimated from the diagram showing polarity of electrocardiogram leads I, II, III, aVL, aVF and aVR. To obtain the frontal axis of a QRS complex:

• 1
  

  Identify the lead in which the R and S waves are most nearly of equal size.

  
  
• 2
  

  Look at right angles (190° and 290°) to the lead identified in step 1.

  
  
• 3
  

  One of the leads identified in step 2 will be predominantly positive, the other predominantly negative.

  
  
• 4
  

  The predominantly positive lead identified by step 3 is approximately the QRS axis (depolarisation towards a lead produces a positive deflection).

  
  
• 5
  

  The approximate QRS axis obtained from step 4 can be made more accurate by estimating the equiphasic lead (step 2) more accurately by ‘imagining’ it between actual leads.

If all leads appear equiphasic, the QRS axis is described as indeterminate; this is rarely normal.

Pulse oximetry

Pulse oximetry has been advocated as a screening tool for CHD in newborns. Because newborns with complex CHD will often deteriorate within 48 hours of age, oximetry would be performed ideally within 24 hours of birth. However, saturations in newborns vary considerably during the first 24 hours, which can increase the false-positive rate. Most healthy newborns are now discharged before 24 hours of age, which limits the use of this technique. Oximetry should be performed on the foot of a baby breathing air. A value of less than 95% is found in about 5% of apparently well infants ( ). If these infants are further evaluated (by repeating the test initially), few cases of important structural heart disease are overlooked and some other potentially unwell infants are also detected. The American Heart Association and American Academy of Pediatrics have recently reviewed the question of pulse oximetry screening after 24 hours of age in some detail ( ). Ten studies with a population of 123 846 infants were summarised, with a false-positive rate of 0.035% when screening was done after 24 hours. Most studies used a cut-off of 95%. The detection rate for many conditions was good, but the authors conclude that additional studies are needed to determine whether this practice should become a standard of care.

Hyperoxia test and blood gas analysis

The hyperoxia (or nitrogen washout) test was described in the era before echocardiography was available and was designed to help distinguish cardiac from respiratory cyanosis without resorting to cardiac catheterisation. Babies with cyanotic heart disease usually show little rise in arterial oxygen tension in response to increased inspired oxygen. A rise of P a o ₂ to a value below 20 kPa after 10 minutes in 85% or more inspired oxygen makes heart disease likely, whereas an increase in P a o ₂ above 20 kPa makes respiratory disease likely. There are some exceptions to this pattern in that babies with desaturating cardiac disease with high lung blood flow (as in unobstructed TAPVC and double-inlet ventricle, for example) will pass, whereas those with very severe respiratory disease and with PPHN may fail.

When it is essential to have an accurate measurement of arterial oxygen content, an arterial blood sample must be obtained, and further information of importance in the management of ill infants will also be available from a blood gas analysis. Transcutaneous oxygen tension monitors placed on the right upper chest (that is, preductal) can be used instead of arterial sampling as a screening test if other information is not required. Oxygen pulse saturation monitors will not provide the same assurance of a pass, as an infant will show 100% saturation at a P a o ₂ value well below 20 kPa. The role of the hyperoxia test has therefore changed since its inception, but it is still helpful in two circumstances:

• 1
  

  When a well baby seems dusky and there is uncertainty as to whether a cyanotic cardiac condition is present. A failed transcutaneous or pulse oximeter hyperoxia test strongly points to cyanotic heart disease.

  
  
• 2
  

  A well baby with signs of heart disease who looks pink may fail the hyperoxia test, thus alerting the physician to the presence of a more complex lesion.

Echocardiography

Transthoracic echocardiography has revolutionised the diagnosis and management of neonatal heart disease. The non-invasive, immediate and portable nature makes this modality ideally suited to the investigation of even the smallest babies. It can define structure and function and has resulted in a dramatic reduction in the need for diagnostic cardiac catheterisation. It is now widely used to guide interventions such as balloon atrial septostomy on the intensive care unit.

The sequential and segmental approach forms the basis of diagnosis of all CHD. A detailed description of this is beyond the scope of this chapter but can be found in . This systematic approach ensures that subtle complex problems are not overlooked even in the most complex malformations. All examinations should begin with indirect evaluation of atrial situs using the great vessels at the level of the diaphragm ( Figs 28.11 and 28.12 ). This is followed by establishing the position of the cardiac apex in the chest from a subcostal view. The same echocardiographic window allows identification of the systemic and pulmonary venous drainage and evaluation of the atrial septum. This is followed by establishing the AV connection and assessment of the AV valves. Next, the position and morphology of the ventricles are established and the ventricular septum is assessed; this is most easily viewed from the cardiac apex. Following this, the ventriculoatrial connections are documented together with the relationship of the great arteries. Assessment of the semilunar valves is followed by documentation of the coronary arteries. From the parasternal views, the branch pulmonary arteries are identified and the aortic arch with the head and neck vessels seen from the suprasternal position. Finally, assessment of function is evaluated using m-mode from a parasternal long-axis view.

Diagrammatic representation of echocardiographic images of arrangement of great vessels at the level of the diaphragm in: (A) normal atrial situs, (B) mirror-imaged arrangement, (C) right and (D) left atrial isomerism.

Schematic representation of: (A) normal situs, (B) mirror-imaged arrangement, (C) right and (D) left atrial isomerism.

All ultrasound modalities have a role in evaluating the cardiovascular system ( Table 28.9 ). Newer ultrasound modalities such as three-dimensional and four-dimensional imaging as well as new Doppler techniques including Doppler tissue imaging and strain imaging are becoming more widely used in the management of CHD but have limited applications in routine neonatal practice at present. More detailed descriptions of these techniques are found in other sources ( ).

Standard two-dimensional imaging gives anatomical detail. Doppler identifies or clarifies shunt lesions and regions of turbulent flow and allows quantification of stenosis by measuring blood velocity. This enables calculation of a pressure difference across a valve or between ventricles through a VSD using the modified Bernoulli equation ( P = 4 V ² , where P = instantaneous peak systolic pressure gradient in mmHg, V = velocity distal to the site of obstruction in m/s).

Standard echocardiographic windows and images of the heart are shown in Figure 28.13 ; examples of clinical scans are given in Figures 28.14–28.16 . Transthoracic echocardiograms may be technically difficult in babies with severe respiratory disease on assisted ventilation. Many of these infants are premature and of low birthweight. As echocardiographic skills become more widespread, telemedicine provides the means whereby neonatal units can collaborate with cardiac centres to analyse recorded echocardiographic studies, helping in the decision-making about whether a baby needs transfer to a tertiary cardiac unit ( ).

(A) Diagram illustrating echocardiographic cross-sectional planes (two-dimensional). The long-axis plane is approximately sagittal; the four-chambers plane is approximately frontal; the short-axis plane is approximately transverse. (B–F) Diagrammatic representations of normal, cross-sectional views. (B) Long-axis cut as seen with the transducer in the parasternal position. (C) Four-chambers cut as seen from the subxiphoid site. (D) Semi-long-axis cut of the aortic arch as obtained from the suprasternal view. (E) High long-axis cut (parasagittal) to show the ductus arteriosus. (F) Short-axis cut through the great arteries just above the heart. Ao, aorta; Dao, descending aorta; Fo, foramen ovale; LA, left atrium; lpa, left pulmonary artery; LV, left ventricle; m, mitral valve leaflets; PA, pulmonary artery; RA, right atrium; rpa, right pulmonary artery; RV, right ventricle; svc, superior vena cava; t, tricuspid valve leaflets.

(Reproduced from .)

(A) Apical four-chamber view with colour flow showing small mid-muscular ventricular septal defect (VSD). (B) Apical four-chamber view of an atrioventricular septal defect with a common atrioventricular valve orifice (CAVVO) and moderate atrial and ventricular components. The ventricles are balanced. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. (C) Apical four-chamber view showing small hypertrophied right ventricle with small tricuspid valve in a patient with pulmonary atresia and intact ventricular septum (hypoplastic right heart). (D) Apical four-chamber view showing hypoplastic left-heart syndrome with small hypertrophied left ventricle (see Fig. 28.20 ). (E) Apical four-chamber view of double-inlet left ventricle with VSD and hypoplastic right ventricle. (F) Apical four-chamber view of dilated cardiomyopathy with severe left atrial and left ventricular dilatation. Mitral regurgitation is seen on colour flow mapping.

(A) Parasternal long-axis view of a patient with tetralogy of Fallot showing subaortic ventricular septal defect. Note the flow from right ventricle to aorta seen on the colour flow mapping. Ao, aorta; LV, left ventricle; RV, right ventricle; VSD, ventricular septal defect. (B) Parasternal long-axis view showing diagnostic arrangement of the great vessels in transposition of the great arteries, which have a parallel arrangement as they arise from their respective ventricles. Ao, aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RV, right ventricle.(C) Subcostal four-chamber view of the atrial septum showing large secundum atrial septal defect with left-to-right flow seen on colour flow mapping. ASD, atrial septal defect; LA, left atrium; RA, right atrium; SVC, superior vena cava. (D) Suprasternal view showing aortic arch with coarctation. Narrowed area of aortic arch highlighted with flow disturbance seen on colour flow mapping.

(A) Apical four-chamber view showing global pericardial effusion (EFF, effusion). (B) Apical four-chamber view showing tricuspid valve vegetation in bacterial endocarditis (VEG, vegetation). Colour flow mapping shows moderate tricuspid regurgitation associated with the vegetation. (C) Volume-rendered three-dimensional echo image of a secundum atrial septal defect seen from the subcostal projection. (D) Volume-rendered three-dimensional echo image of multiple apical muscular ventricular septal defects seen in a four-chamber projection. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Cardiac catheterisation

Cardiac catheterisation and angiography was once the principal means of investigating babies with CHD. It may be diagnostic for anatomical or haemodynamic information or may be therapeutic. Diagnostic catheterisation is now rarely required in the newborn baby with present-day ultrasound capability and other non-invasive imaging modalities. When it is, usually only a small amount of information is required in order to complement that already obtained by echocardiography. Cardiac catheterisation in small children carries a small but definite risk and almost inevitably requires general anaesthesia. This will influence cardiac physiology and the relevance of the information obtained.

Magnetic resonance and computed tomographic imaging

MRI provides excellent anatomical images, but, in the newborn, echocardiography often provides adequate information. The range of uses for cardiac MRI scanning in the newborn is continuing to expand as greater experience is obtained in older children and scanning technology improves. It can provide useful non-invasive anatomical information about pulmonary arterial abnormalities previously only obtainable from angiography. MRI involves no radiation hazard, but does require sedation or general anaesthesia in an environment where detailed monitoring is rather more complicated to achieve. In contrast, computed tomographic (CT) imaging, which requires shorter acquisition times and can frequently be performed with sedation alone, does have a role as a non-invasive imaging technique in neonates. It provides excellent information about aortic arch anatomy and other vascular structures ( Fig. 28.17 ) and the relationship of the vascular structures to the airways but its drawback is the radiation dose required to acquire such images.

(A) Volume-rendered computed tomography angiogram (anterior view) showing a right-sided aortic arch with aberrant left subclavian artery (LSCA). (B) Same image (posterior view). This aortic arch anatomy is usually associated with a left-sided arterial duct arising adjacent to the origin of the aberrant left subclavian artery creating a loose vascular ring. (C) Axial contrast-enhanced image, in the same patient, showing a right-sided arch with the origin of LSCA arising posterior to the trachea.

General principles

In principle, medical management for CHD is largely supportive (e.g. heart failure) whereas significant structural abnormalities usually require intervention. Continued improvement in surgical results for congenital cardiac malformations has been one of the triumphs of modern paediatric cardiology. Surgical mortality for malformations, which were, up to recently, considered untreatable (e.g. hypoplastic left-heart syndrome (HLHS)) is now very acceptable. In addition, improvements in surgical results have meant a major shift in surgical emphasis away from surgical palliation towards primary neonatal correction of structural abnormalities with restoration of normal physiology wherever possible. This has been further facilitated by the advances occurring in neonatal intensive care both pre- and postoperatively.

Attention to the general aspects of medical care to achieve stability and optimise condition prior to transfer and intervention of any kind is a very important aspect of minimising morbidity and mortality for any cardiac condition. There are some specific areas related to the care of neonates with cardiac disease that require further mention.

Ductal manipulation

Establishing and maintaining an open DA is a crucial part of the resuscitation of babies with duct-dependent pulmonary or systemic circulations and usually greatly improves oxygenation in TGA. Prostaglandin E ₁ and E ₂ will both dilate the DA. Dosage regimens for both drugs are given in Table 28.10 . Acute side-effects of prostaglandin include apnoea, jitteriness, convulsions, diarrhoea, flushing and fever and are dose-dependent. These are usually manageable without loss of therapeutic effect by stopping the infusion for a few minutes and restarting it at a lower dose. Long-term oral or nasogastric use is described ( ) but of limited value. Manipulation of the DA in order to close it is considered on pages 645–647 .

Table 28.10

Prostaglandin (PG) dosage regimens

DRUG AND ROUTE	DOSE	COMMENT
PGE 1 i.v.	0.005–0.1 µg/kg/min	For severe cyanosis or shock, start at higher dose range for both drugs and increase at 15–30-minute intervals to maximum if no response. More than threefold increase in dose rarely needed. Side-effects increase with higher doses
PGE 2 i.v.	0.005–0.05 µg/kg/min

 

NB. In antenatally diagnosed duct-dependent congenital heart disease, elective prostaglandin infusion should be started at the lowest dose (5–10 ng/kg/min) as this will minimise side-effects whilst maintaining ductal patency.

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