<scp>ISUOG</scp> Practice Guidelines (updated): fetal cardiac screening

Abstract

The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) is a scientific organization that encourages sound clinical practice and high-quality teaching and research related to diagnostic imaging in women's healthcare. The ISUOG Clinical Standards Committee (CSC) has a remit to develop Practice Guidelines and Consensus Statements as educational recommendations that provide healthcare practitioners with a consensus-based approach, from experts, for diagnostic imaging. They are intended to reflect what is considered by ISUOG to be the best practice at the time at which they are issued. Although ISUOG has made every effort to ensure that Guidelines are accurate when issued, neither the Society nor any of its employees or members accepts liability for the consequences of any inaccurate or misleading data, opinions or statements issued by the CSC. The ISUOG CSC documents are not intended to establish a legal standard of care, because interpretation of the evidence that underpins the Guidelines may be influenced by individual circumstances, local protocol and available resources. Approved Guidelines can be distributed freely with the permission of ISUOG ([email protected]). Effective fetal cardiac screening should maximize detection of structural anomalies and (according to available expertise and resources) abnormalities of function and rhythm, as part of routine prenatal care. This document provides recommendations for low-risk fetal cardiac ultrasound screening during the second trimester, updated from previously published Guidelines1. The practical implementation of late first-trimester and early second-trimester cardiac screening, when technically feasible, is also considered. These Guidelines encourage the use of color flow Doppler ultrasound and introduce new sections on quality assurance and the use of a checklist (Appendix 1). Healthcare workers can also use these Guidelines to identify pregnancies at risk for genetic anomalies2 and to provide timely guidance for patient counseling, obstetric management and multidisciplinary care. Cases with suspected heart anomalies and/or those at increased risk require fetal echocardiography3-6. Congenital heart disease (CHD) has a prevalence of 8.2 per 1000 live births and is a leading cause of infant morbidity and mortality7. Prenatal diagnosis can improve birth outcome prior to intervention8, particularly for certain types of cardiac lesion9-15. Prenatal awareness of CHD and parental education allow preparation for the birth of a neonate that will require specialized care and services. The impact of prenatal diagnosis may also be relevant to long-term neurodevelopmental outcome16, 17 and it maximizes options for the family. However, prenatal detection rates vary widely in different geographic regions and for various types of CHD, with fewer than one half of cardiac anomalies being identified before birth7, 18, 19. Some variation can be attributed to differences in examiner ability, transducer frequency, patient body habitus, abdominal scars, gestational age, amniotic fluid volume and fetal position20-23. Continuous feedback-based training of healthcare professionals, a low threshold for echocardiography referrals, use of standardized ultrasound protocols and easy access to fetal-heart specialists can improve the performance of a screening program14, 24-26. Details of the grades of recommendation and levels of evidence used in ISUOG Guidelines are given in Appendix 2. Despite the well-documented utility of the four-chamber and outflow-tract views, one should be aware of the potential diagnostic pitfalls that can prevent timely detection of CHD27-29. Detection rates can be optimized by performing a thorough screening examination of the heart, recognizing that the four-chamber and three-vessel views require much more than a simple count of cardiac structures, understanding that some lesions are not discovered until later in pregnancy, and being aware that certain types of abnormality (e.g. transposition of the great arteries, aortic coarctation) may not be evident in the four-chamber plane alone. Complementing the four-chamber view with outflow-tract and great-vessel views in the cardiac screening examination has played an important role in improving detection of CHD24, 30, 31. The cardiac screening examination is performed optimally between 18 and 22 weeks' gestation (GOOD PRACTICE POINT). Screening at 20–22 weeks is less likely to require an additional scan for completion of this evaluation when compared with screening at 18–20 weeks, although many patients would prefer to know about major defects as early as possible in the pregnancy32. Many anatomical structures can be visualized satisfactorily beyond 22 weeks and some major cardiac defects may be identified during the late first and early second trimesters, especially when increased nuchal translucency thickness raises suspicion or if attempts are made to visualize the fetal heart during earlier scans33-39. Higher-frequency probes will improve the likelihood of detecting subtle defects, at the expense of reduced acoustic penetration. The highest possible transducer frequency should be used for all examinations, recognizing the trade-off between penetration and resolution. Tissue harmonic imaging provides improved images, especially for patients with increased abdominal wall thickness and during the third trimester of pregnancy40 (GOOD PRACTICE POINT). Cross-sectional grayscale imaging is the basis of a reliable fetal cardiac scan. System settings should emphasize a high frame rate, with increased contrast and high resolution. Low persistence, a single acoustic focal zone and a relatively narrow image field should also be used and are usually incorporated in cardiac presets. Advanced postprocessing of images has also been added to current ultrasound systems and contributes further to improved image display (GOOD PRACTICE POINT). Images should be magnified until the heart fills at least one-third to one-half of the screen. The cine-loop feature should be used to assist the real-time evaluation of normal cardiac structures, for example, to confirm movement of heart valve leaflets throughout the cardiac cycle. Image magnification and use of cine-loop may also help in identifying abnormalities (GOOD PRACTICE POINT). For the structures and views noted in this Guideline, we recommend archiving of still frames and videoclips, while also considering local/national standards. The examination should be recorded in a manner that will allow subsequent review to verify its diagnostic adequacy, with appropriate patient identification and labeling of image laterality and orientation, when appropriate (GOOD PRACTICE POINT). The cardiac screening examination should include the fetal situs and the four-chamber, outflow-tract and great-vessel views30, 31, 41-49. This evaluation increases the detection rates for major cardiac malformations above those achievable using the four-chamber view alone24, 30, 31, 50, 51. The inclusion of outflow-tract and great-vessel views enables detection of anomalies such as tetralogy of Fallot, transposition of the great arteries, double-outlet right ventricle and truncus arteriosus44-47, 52-57. This standardized workflow (Appendix 1) can also identify abnormalities of the semilunar valves, such as aortic and pulmonary stenosis, which may progress in severity as the pregnancy advances58, 59 (GRADE OF RECOMMENDATION: C). To assess cardiac situs, it is necessary first to determine fetal laterality, i.e. to identify fetal right and left sides, based on the position of the fetus in utero, prior to ascertaining that both stomach and heart are on the left side of the fetus48, 60-62. In the second trimester, the heart is positioned in a horizontal plane within the chest, held in place by the fetal liver, which extends to the left side of the fetal abdominal wall63, 64. A transverse sweep with cephalad movement of the transducer, from the fetal abdomen towards the fetal chest, allows visualization of the abdominal situs and the four-chamber view (Figures 1 and 2). The abdominal situs is obtained at the level of the standard abdominal circumference measurement, with the stomach visible on the left side. Additionally, cross-sectional views of the descending aorta and inferior vena cava are seen on the left and right sides of the spine, respectively (Figure 3). Identification of normal abdominal situs is a surrogate for normal atrial situs (situs solitus, i.e. right atrium to the right and left atrium to the left). Assessment of the four-chamber view involves careful evaluation of specific criteria. The main elements for examination of the four chambers are shown in Table 1 and Figures 4 and 5. A normal heart is usually no larger than one-third of the area of the chest. A small amount of pericardial fluid is commonly seen during the second and third trimesters (≤ 2 mm in thickness, at end-systole) and is a normal finding65. Some views may also reveal a small hypoechogenic rim around the fetal heart, and care should be taken not to mistake this for pericardial effusion66. The heart is situated mainly on the left side of the chest and its long axis normally points to the left by about 45 ± 20° (2 SD)67 relative to the anteroposterior axis of the chest (Figure 4). Careful attention should be paid to cardiac axis and position, which can be evaluated easily even if the four-chamber view is not visualized satisfactorily68. Situs abnormalities should be suspected when the fetal heart and/or stomach are not found on the left side. An abnormal cardiac axis increases the risk of a cardiac malformation, especially involving the outflow tracts69. This finding may also be associated with a chromosomal anomaly. Abnormal displacement of the heart from its normal anterior left position can be caused by a diaphragmatic hernia or space-occupying lesion, such as congenital pulmonary airway malformation. Position abnormalities can also be secondary to fetal lung hypoplasia or agenesis70. A shift of the axis to the left may also occur with fetal gastroschisis and omphalocele. Normal heart rate and regular rhythm should be confirmed. The normal rate ranges from 120 to 160 beats per min (bpm). Skipped (or ectopic) beats are the most common rhythm disturbance. Often, these are benign and resolve spontaneously. In low-risk populations, they are not associated with an increased risk of structural fetal heart disease71, 72. However, frequent episodes (more than every three to five beats) or a persistently irregular cardiac rhythm (> 1–2 weeks) are an indication for further assessment5, 6, 71, 73-75. Bradycardia, often associated with transducer pressure on the abdomen, is observed transiently in normal second-trimester fetuses. Persistent bradycardia (≤ 110 bpm) in a well fetus requires timely evaluation by a fetal cardiac specialist76, 77. Possible causes include frequent blocked atrial ectopic beats, atrioventricular block and sinus bradycardia78, 79. Repeated heart-rate decelerations during the third trimester can be caused by fetal hypoxia. Mild, transient tachycardia (160–180 bpm) can occur as a normal variant during fetal movement. Persistent tachycardia (≥ 180 bpm)78, 80, however, should be evaluated further for more serious tachydysrhythmias or fetal hypoxia. Both atrial chambers normally appear similar in size and the foramen ovale flap moves within the left atrium. The lower rim of atrial septal tissue, the septum primum, should be present and forms part of the cardiac ‘crux’, the point at which the lower part of the atrial septum meets the upper part of the ventricular septum and where the atrioventricular valves insert. Pulmonary veins can often be seen entering the left atrium and, when technically feasible, visualization of at least one of these veins on B-mode is recommended. Although color flow can facilitate their visualization, this should not be considered mandatory. color Doppler ultrasound should be B-mode images to The a that the right ventricular is seen the and is in identification of the right The left ventricular and forms the of the Both should appear similar in size and no evidence of Although ventricular can occur as a normal variant in the third trimester of pregnancy, in further of the left heart and pulmonary can be important causes of this The ventricular septum should be for cardiac wall defects from the to the and, if a sweep should be performed which at the most part of the septum and moves towards the outflow defects may be to The septum is best seen when the of is to the ultrasound is to the ventricular a the may be suspected because of an acoustic septal defects can be to confirm if the ultrasound imaging to provide a of especially if the fetal size and position are However, in most these are of clinical and may even in atrioventricular valves should be seen to and The septal of the valve is the septum to the when compared with that of the valve normal Abnormal of the atrioventricular valves can be a finding for cardiac anomalies such as atrioventricular septal The left and right ventricular outflow-tract views and the three-vessel and views are considered an part of the fetal cardiac screening is important to of the great arteries, to the their size and their position relative to and normal and of the semilunar A obstetric ultrasound of 18 the practice of the four-chamber view and, when technically feasible, evaluation of the outflow the routine second-trimester ultrasound that an four-chamber view also associated with evaluation of the outflow rates for the for the and for both outflow of the ventricular outflow and as a that the great are in major in their size should to further they from their three should be confirmed. in a normal the first great from the left ventricle and its anterior wall is with the ventricular not this to be the in a normal the great that the this to be the pulmonary the great should In to the outflow-tract views, the related and should be used to help anomalies involving the outflow aortic and left vena and that may be include transposition of the great arteries, tetralogy of and aortic and pulmonary The more cephalad and more evaluation of the position of the aortic and and their to the is particularly for detection of aortic abnormalities such as of the and right a transverse sweep with cephalad movement of the transducer from the four-chamber view towards the upper chest allows of the cardiac structures and provides the views necessary to of the outflow and and views, and (Figures 1 and (GOOD PRACTICE POINT). In an these views can be obtained with relative the fetal is additional examination time or a second examination may be the outflow-tract and great-vessel views are obtained by movement of the transducer towards the fetal by small in from a four-chamber to visualize the normal of the aorta and main pulmonary at their Details of the pulmonary can also be a variation in the for the outflow in the fetus has been the This from a four-chamber view of the heart, with the transducer first being towards the fetal right This performed more easily when the septum is to the ultrasound may require visualization of the especially the part of the septum that is in with the anterior wall of the also allows visualization of the both the view is the transducer is cephalad until the pulmonary is observed with a to that of the The relative of the and are best using than still The and are additional views of the aorta and pulmonary and their with the vena cava and These views can be obtained by further cephalad movement of the transducer towards the fetal from the by small in to the best possible for the different structures in The as well as the transverse aortic can also be at this The view the of a great from the left ventricle (Figure and from the of the should be between the ventricular septum and the anterior wall of this to of the However, it is the of the and from it that this as the The aortic valve should freely and should not be is possible to the aorta its from which three the However, views of the aortic and and of the are not considered part of the routine cardiac screening examination (Figure The view to identify ventricular septal defects and as well as aortic valve abnormalities that are not visible in the four-chamber the between the various structures in the and (Figures is a of many cardiac as specific still images, it is that the in the plane of the pulmonary and and aortic a of that may vary on the of the transducer, the fetal and the plane in a still frame (Figure This is likely to be more reliable during live or on review of a cine-loop than from a of still images The view the of a great the pulmonary from the right ventricle (Figures and and a The pulmonary valve should freely and should not be The normal pulmonary towards the left of the more which is seen in is usually larger than the aorta during fetal and the aorta anterior and cephalad to the at a right this the vena cava is seen to the right of the The and as a to the four-chamber with the of the of the cardiac screening the to the pulmonary aorta and vena cava and their relative and (Figure This involves an of and left to the are the pulmonary aorta and right vena The pulmonary is the most anterior and the vena cava is the most relative should from left to abnormalities associated with a normal four-chamber such as transposition of the great arteries, tetralogy of Fallot, right common and pulmonary with ventricular septal will be abnormal in the the a view cephalad with to the in which the transverse aortic is visualized and its with the (Figure This view a transverse plane that the main pulmonary in with the The normal transverse aortic is positioned to the right of the main pulmonary The can be identified as a a small The normal and aortic to the left of the and an The normal right vena cava and the normal are also seen in this The aortic is more to image both may require some transducer from a The is likely to detection of lesions such as of the right aortic and aortic using the and may and management (e.g. prenatal for of (e.g. in transposition of the great and care (e.g. for as well as of potential airway from Although the use of color flow Doppler is not considered in these with its use and it to routine screening is flow is an part of a fetal and its role in the diagnosis of CHD be can be incorporated during routine screening if the with its In a normal fetal heart, color flow will flow the atrioventricular and semilunar valves and great may also facilitate imaging of the various cardiac For example, flow visualization in the aorta and in identifying the as well as abnormal such as atrioventricular valve and flow in the and aortic may also a in the evaluation of cardiac in and may further improve detection rates of major CHD in low-risk color Doppler settings include the use of a narrow color positioned the area of for than the image of the the color to a specific will the frame rate and color image which will allow display of flow valves and image or real-time routine second-trimester screening, the color flow should be at for structures and This and low color flow are usually incorporated in cardiac presets. However, the should be lower if structures (Figure identified as or suspected of an abnormality on routine cardiac ultrasound screening are for a fetal (GOOD PRACTICE POINT). For with a risk for CHD, i.e. when their risk is above that of the fetal echocardiography is also in to routine cardiac screening, on such as local clinical examiner and of screening (GOOD PRACTICE POINT). However, a high of with a CHD are patients any risk or the of quality screening, with timely if this an Healthcare practitioners should be with common for for cardiac evaluation by fetal 6, of risk are beyond the of this Guideline, a of common fetal and patient associated with an increased risk of CHD is shown in Table For example, nuchal translucency thickness mm at weeks' gestation is an indication for a cardiac even if the within the normal echocardiography is best performed by a is with prenatal diagnosis of CHD as well as with the management and The is to a of the fetal heart and, if an abnormality is to about the long-term and outcome and management Prenatal detection of a CHD should also the high prevalence of that is associated with the of fetal it is important to various of the cardiac screening examination to ensure of the image of the standard appropriate interpretation of the views and performance on ultrasound the use of cardiac and appropriate This image quality and the to the in the various color Doppler is the settings should be optimized and the to the structures being (Figures and of prenatal detection of CHD that not to about of However, to abnormal heart on a technically appropriate view for of quality is important for ultrasound and fetal cardiac An based on quality for interpretation and of still images or is an important the use of which is and may the of prenatal diagnostic improving timely detection of ISUOG encourages imaging practice to review local detection rates and diagnostic of CHD and to provide further training as Screening for CHD in the first trimester has been shown to be in low-risk However, it is neither performed nor considered mandatory. In or in which this is early screening can be at the time of the nuchal translucency scan. for early screening include visualization of the heart within the chest and of regular should be in to the small size of the fetal heart in early the rate of visualization of the cardiac structures on is gestational may be the use of to their and use of color and/or high-quality Doppler flow in to grayscale imaging. and Doppler ultrasound should be to the color the to visualization of the flow the small structures in the first-trimester fetal Doppler should be used for screening the four-chamber view and the for The most ISUOG that the various Doppler may be used between and weeks for certain clinical screening for cardiac it is important to the which should be and the time should be as as possible no than The are as part of a early cardiac screening (Figure (GOOD PRACTICE POINT). on grayscale to the normal position of the stomach and heart, both of which should be on the left side of the is also important to assess the cardiac as this is a for using grayscale and color and/or Doppler imaging. the is visualized for of using color and/or Doppler to the aortic and of left and right outflow at this early gestational is often and to both and if early cardiac screening is performed at the time of the nuchal translucency this should be based mainly on situs and the four-chamber view and any suspicion of CHD be at this the patient should be for early fetal These Guidelines should be ISUOG Practice Guidelines fetal cardiac Ultrasound The to from for time and expertise in the cardiac for these is not to this as no new or in this The is not for the or of any by the than should be to the for the