(a) The five axial views for optimal fetal heart screening. The colour image shows the trachea, heart and great vessels, liver and stomach, with the five planes of insonation indicated by polygons corresponding to the grey-scale images, as indicated. (I) Most caudal plane, showing abdominal situs. (II) Four-chamber view. (III) Left ventricular (LV) outflow tract. (IV) Right ventricular (RV) outflow tract/three-vessel view (3VV). (V) Three vessels and trachea view (3VTV). Ao aorta, dAo descending aorta, PA pulmonary artery, SVC superior vena cava, Tr trachea (Modified with permission from Carvalho et al. and Yagel et al. © ISUOG [66, 67]). (b) Increase in number referrals for suspected cardiac abnormalities, 2003–2013, Fetal Medicine Unit, St George’s Hospital, London, UK
In practice, it is difficult to ensure that guidelines are followed at national and international level in order to deliver equal care to all pregnant women worldwide. It is well accepted that the effectiveness of any screening programme is highly dependent on training, so that professionals responsible for screening can deliver such care [70–72]. Data from the UK National Institute for Cardiovascular Outcomes Research  shows that the percentage of infants requiring surgery or catheter intervention for CHD has increased over the years since 2003. A steeper increase around 2010 suggests this may be related to introduction of the FASP cardiac protocol.
1.5 Fetal Cardiology Assessment
The role of a fetal cardiologist, beyond making an accurate diagnosis, is to provide the parents with a comprehensive, evidence-based picture of the outcome possibilities, starting with pregnancy, through childhood, and into adult life . This is not an easy task. Surgical results and outcomes are constantly changing and naturally, counselling is lesion specific (e.g. tetralogy of Fallot) and within each lesion, it is further tailored to the scan findings in each individual fetus (e.g. tetralogy of Fallot with pulmonary stenosis versus pulmonary atresia).
Ideally, fetal cardiac assessment happens within a fetal medicine unit or in close collaboration with a fetal medicine specialist to facilitate a multidisciplinary approach. In the fetus with a cardiac abnormality, risk of extra-cardiac, chromosomal or genetic abnormalities and the option of invasive tests (amniocentesis or cordocentesis) need to be discussed. The first step, however, is to establish an accurate diagnosis. Similarly to postnatal cardiology, it is important to adopt a structured approach, often based on a sequential segmental analysis (SSA) of the heart [75–77].
1.5.1 Structural Fetal CHD
Being able to confirm normality of the fetal heart is as important as making the diagnosis of CHD, simple or complex. For the pregnant woman who is aware of the increased risk of cardiac malformation in her unborn child, reassurance is of paramount importance. For those referred because of a suspected abnormality, accuracy of diagnosis forms the platform for subsequent pregnancy management. Neither scenario can be underestimated. In both instances, it is important to approach the fetal heart in a logical manner. The SSA offers a step-by-step approach to describing the cardiac anatomy in normal and malformed fetal hearts. Determination of situs, cardiac connections and associated defects facilitates understanding of the pathophysiology of abnormalities, which is essential for counselling families.
When applied to the fetus, the SSA differs, in that prior to ascertaining abdominal situs and by inference, atrial arrangement, it is imperative to determine fetal laterality [69, 77]. This is achieved by assessing fetal lie within the maternal abdomen so that the right and left sides of the fetus can be established. Subsequently, the same 7postnatal rules and definitions used in the SSA apply.
The diagnosis of major CHD involving abnormalities of cardiac connections is often straightforward, such as in tricuspid atresia and complete transposition of the great arteries (Fig. 1.2). More complex lesions, including those seen in the setting of atrial isomerism, can also be identified accurately but are also more challenging. It can be more difficult to exclude relatively minor defects, e.g. a small to moderate perimembranous ventricular septal defect, than to diagnose a complex abnormality. If images are suboptimal, additional scans may be needed.
(a) Four-chamber view obtained from a fetus with tricuspid atresia, obtained at 32 weeks of gestation. Left panel, 2D and right panel, with colour Doppler. The arrow points to the absent right atrioventricular connection. (b) Images obtained from a fetus at 23 weeks of gestation, with complete transposition. Left panel (2D) and right panel (e-flow mapping) are sagittal views of the fetus showing the parallel arrangement of the two vessels with an anterior aorta and posterior pulmonary artery. (c–e) Images obtained from a hydropic fetus at 25 weeks of gestation, with supraventricular tachycardia, partially controlled on dual maternal therapy. (c) Shows fetal ascites, (d) four-chamber view shows cardiomegaly and mitral and tricuspid regurgitation, (e) M-mode recoding shows 1:1 atrioventricular conduction with heart rate = 215 bpm. Pretreatment rate was 270 bpm. The rhythm was sinus a few days afterward. Ao aorta, LA left atrium, LV left ventricle, RA right atrium, RV right ventricle, PA pulmonary artery, * rudimentary RV
An important consideration in fetal heart disease relates to potential progression of obstructive lesions as pregnancy advances [78–80]. A classical example is seen in critical aortic stenosis in mid-pregnancy that is likely to progress to hypoplastic left heart syndrome (Fig. 1.3). Also to be taken into account in predicting postnatal presentation of CHD are the physiological perinatal circulatory changes. In addition to closure of the foramen ovale, ductus arteriosus and ductus venosus, changes in right and left ventricular preload and afterload may alter the appearances of the normal and abnormal heart. This is particularly relevant in cases of borderline left ventricle when trying to predict if it will be able to sustain a biventricular circulation after birth.
(a–c) Images obtained from a fetus at 21 weeks of gestation with critical aortic stenosis. (a) Four-chamber view in diastole on 2D (left panel) and colour flow (right panel) shows a dilated left atrium. The left ventricle reaches the cardiac apex and shows areas of hyperechogenicity. (b) Left ventricular outflow tract view in systole. Note the presence of important mitral regurgitation and a narrow jet (arrow) of forward flow across the aortic valve. (c) Pulsed wave Doppler shows high aortic velocity (290 cm/s, normal for gestation ~60–70 cm/s). (d–f) Images obtained from a fetus at 14 weeks of gestation with hypoplastic left heart syndrome. (d) Four-chamber view in diastole, on 2D (left panel) and e-flow mapping (right panel). Note filling of the right ventricle only. (e) Transverse view through upper mediastinum at the level of the three-vessel view. E-flow mapping shows a large ductal arch only. No aortic flow seen at this level. (f) Sagittal view demonstrates forward flow across the ductal arch and reversed flow in the transverse aortic arch. Ant anterior, LA left atrium, LV left ventricle, Post posterior, RA right atrium, RV right ventricle, VMax maximal velocity
1.5.2 Fetal Arrhythmias
Fetal cardiac rhythm should be regular and heart rate roughly ranges from 120 to 160 beats per minute (bpm). M-mode echocardiography and pulsed-wave Doppler are the most commonly used methods to assess rhythm in the fetus, based on simultaneous recording of atrial and ventricular activities . The most common rhythm disturbances are intermittent extrasystoles, which are of little clinical relevance. Arrhythmias that potentially affect fetal well-being or have postnatal implications for the newborn and child are relatively uncommon. Less than 10 % of referrals are due to sustained tachy- or bradyarrhythmias .
Intermittent extrasystoles are frequently encountered, usually of atrial origin and generally considered to be ‘benign’. They are often described as ‘skipped’ or ‘missed’ beats, which can cause a lot of anxiety, even if the vast majority resolve spontaneously and require no treatment. In about 2 % of cases, skipped beats may represent incomplete heart block  or be associated with intermittent tachycardia. Therefore, it is important that these possibilities be excluded. A scan performed locally by the sonographer or obstetrician usually suffices. If heart rate is within normal range, with no fluid accumulation in any fetal compartment and the cardiac screening views are normal, the pregnant woman can be reassured. Urgent referral to a specialist is only warranted in a few selected cases when either heart rate and/or the scan findings are abnormal . If the ectopic beats occur ‘very frequently’ (i.e. the rhythm is irregular most of the time), there is a slightly higher risk of fetus developing a tachyarrhythmia  and a referral is also warranted, after the initial assessment in the local hospital.
Tachycardia is defined as rate ≥180 bpm. If persistent, it may lead to congestive heart failure and hydrops fetalis (Fig. 1.3). If it is intermittent or not, urgent referral to the fetal cardiologist is required. However, not all cases need treatment as sometimes the arrhythmia resolves spontaneously. Thus, if the fetus is stable, close monitoring of fetal heart rate for 24 h or so to determine if the arrhythmia persists may be appropriate, before initiating therapy. If there is sustained tachycardia or it persists for >50 % of the time, or the fetus is compromised, fetal treatment or delivery of the baby (if gestational age ≥37 weeks) is indicated. Choice of medication varies from centre to centre and with experience. Maternal transplacental transfer is the preferred option to deliver the chosen drug to the fetus. Currently, a randomized controlled trial for treatment of fetal tachyarrhythmia is on its early implementation phase .
Traditionally, fetal bradycardia has been defined as rates <100 bpm but current obstetric threshold is 110 bpm . More recently, gestational age-specific heart rates have been developed and centile charts are available . Transient periods of sinus bradycardia during scanning are common and benign. Persistent sinus bradycardia is relatively rare and may be a manifestation of long QT syndrome . More commonly however, fetal bradycardia is due to blocked atrial bigeminy, which typically presents with heart rate around 70–80 bpm. This can be transient or last for days or weeks. Whilst it is well tolerated by the fetus and of no hemodynamic consequence, it is important to differentiate blocked bigeminy from second-degree atrioventricular block with 2:1 conduction . Heart block is often caused by transplacental passage of circulating maternal IgG antibodies (anti-Ro/ SSA and anti-La/SSB), which causes injury to the conduction tissue with subsequent fibrous replacement. Certain forms of CHD can also lead to fetal heart block, notably cases which are associated with left isomerism, but it can also occur in the presence of atrioventricular discordance. The prognosis for autoimmune-mediated complete atrioventricular block is better than if associated with CHD but there still is significant mortality and morbidity. Most survivors require pacemaker implantation in the first year of life .
1.5.3 Inherited Cardiac Conditions
Despite recent advances in genetics and better understanding of inherited cardiac conditions that may confer a 50 % risk to the fetus, little has been reported in fetal life. Inherited cardiomyopathies are relatively uncommon in the fetus . Hypertrophic cardiomyopathy rarely manifests prenatally, but can be associated with Noonan syndrome. Among channelopathies, recent data on prenatal manifestation of long QT syndrome, bradycardia with rates below the 3rd centile for gestational age, has increased interest in identifying affected fetuses . Among aortopathies and related conditions, there are scarce fetal reports, mainly related to the infantile type of Marfan syndrome .
1.5.4 Early Fetal Echocardiography
Initial observations of CHD diagnosed in the first trimester of pregnancy were made by obstetricians utilizing a transvaginal approach [91, 92]. Subsequently, it became clear that the transabdominal route could also be used in clinical practice to image the fetal heart at less than 14 weeks gestation . Over the years, this practice has become more common. The number of fetal cardiologists offering a detailed assessment of the fetal heart at 15–16 weeks has increased but it is not yet universally available. Early scans can be challenging due to the small fetal heart size and additional technical limitations sometimes imposed by fetal position and maternal characteristics. Nevertheless, its clinical utility in high-risk pregnancies has been shown by a number of investigators [94–97]. Similarly to mid-gestation, it is very important that the fetus with CHD identified early in pregnancy be assessed by a multidisciplinary team, especially in cases referred because of increased NT measurements. Figure 1.3 illustrates a case of hypoplastic left heart syndrome diagnosed at 14 weeks in a woman referred with family history of CHD.
1.6 Counselling and Pregnancy Options
Counselling a woman who attends for a fetal echocardiogram should start before the scan is performed. For each family, the perceived risks of encountering an abnormality during the scan and/or the likelihood of the scan being normal should be discussed. Limitations posed by early scans (<16 weeks) should be highlighted. This prepares the woman for what to expect, especially when she is referred due to a suspected abnormality.
Following the diagnosis of any form of CHD, the ultrasound findings are explained to the family, often with the help of diagrams to help them understand the anatomy and pathophysiological implications of the defect. An account of the likely postnatal manifestations of the disease, surgical options, risks and need for long-term follow-up is provided. In cases where progression is expected to occur during pregnancy, the need for serial fetal scans is reinforced. Family consultation is often in the presence of a fetal cardiac nurse specialist who provides the family with ongoing support. An obstetric/fetal medicine assessment should also be arranged on the same day or shortly afterwards to exclude or document extra-cardiac abnormalities and review pregnancy risks for chromosomal abnormalities and genetic syndromes.
The option of an invasive procedure (amniocentesis or cordocentesis) to check fetal karyotype is discussed, often jointly between the fetal cardiac and fetal medicine specialists. Depending on the type of CHD, associated abnormalities and gestational age, the option of TOP, if legally possible, is also discussed. Interrupting the pregnancy often involves induction of labour and may require fetocide, depending on gestational age. In the UK, the Royal College of Obstetricians and Gynecologists recommend this be performed at >22 completed weeks of gestation. Spontaneous fetal demise in the absence of heart failure/ hydrops is uncommon, but the risk is increased if there is an associated chromosomal abnormality (e.g. trisomy 21).
There is growing literature – summarized in a recent meta-analysis, indicating that, in the absence of known chromosomal or genetic abnormalities, the child with major CHD is at increased risk of brain abnormalities (detected on neuroimaging) and neurodevelopmental delay [98, 99]. Most of the reported cases are examples of hypoplastic left heart syndrome and complete transposition. In this analysis, the findings were independent of surgical risk, but it did not provide data to indicate if the origin was fetal or postnatal. On a more recent meta-analysis, there is some evidence to suggest that at least in part, some of these changes occur before birth . However, a survey of experts’ attitudes towards counselling families regarding risks of development delay in CHD advises caution . Any information provided needs to be accurate but is inevitably based on current knowledge, which is limited by the retrospective nature of the published studies and lack of correlation between individual neuroimaging abnormalities and developmental outcome. Further research is required in this important area.
1.7 Perinatal Plan for the Fetus with CHD
One of the strengths of prenatal diagnosis is optimization of perinatal care. Fetuses expected to have neonatal intervention require delivery in a hospital with facilities to stabilize the neonate. In some instances, this needs to be at or close to a cardiac unit. However, local delivery is also possible, depending on the abnormality and available local human and medical resources [102–105].
Ideally, babies with CHD will be delivered at term. For those with critical defects, retrospective data suggest that mortality is lower if delivery occurs at 39–40 completed weeks. Delivery before 39 weeks is also associated with increased morbidity. However, premature delivery may be unavoidable, for example, if there is spontaneous labour or obstetric concern about fetal growth.
The neonatal team will be aware that a child with major or critical CHD is to be delivered and should be aware of the initial postnatal management.
1.8 Changing Pattern of Fetal CHD
Traditionally, fetal CHD meant complex CHD. The defects were often associated with worse prognosis, with many abnormalities leading to a univentricular circulation. For many years, abnormal hearts showing a normal four-chamber view were unlikely to be recognized on routine screening. In the mid-1990s only 3 % of infants with complete transposition undergoing surgery were antenatally diagnosed . With improvements in screening and especially the introduction of outflow tract views, fetal diagnosis of less complex abnormalities with potential for biventricular repair has increased. However, there has also been an increase in detection of CHD that may not require intervention or may be considered variants of normal. This new, emerging pattern of fetal CHD will enhance our understanding of natural history. For example, it is clear that many children with an isolated right aortic arch are asymptomatic  and would have not been diagnosed had it not been for prenatal screening. It also seems that persistence of a left superior vena draining into the coronary sinus as an isolated finding is not uncommon. Nevertheless, when a pregnant woman is referred for fetal cardiology assessment, the anxiety generated is not insignificant and prompt evaluation is required in order to clarify if fetal CHD is present and the potential impact it may have on the child and family.
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