The sonographic approach to the detection of fetal cardiac

Transcription

1 Ultrasound Obstet Gynecol 2002; 19: The sonographic approach to the detection of fetal cardiac Blackwell Science Ltd anomalies in early pregnancy M. BRONSHTEIN* and E. Z. ZIMMER* *Department of Obstetrics and Gynecology, Rambam Medical Center, Technion-Israel Institute of Technology, Faculty of Medicine, Haifa, Israel KEYWORDS: Congenital, Fetus, Heart defect, Ultrasound ABSTRACT Background Transvaginal sonography enables imaging of the fetal heart in various planes and directions in early pregnancy. This study summarizes our experience in early detection of fetal cardiac anomalies. Methods Transvaginal sonographic examination was performed in consecutive fetuses in both high- and lowrisk pregnancies. More than 99% of cases were evaluated at weeks gestation. Examination of the cardiovascular system did not rely on still images of the classic views but instead was performed in a dynamic mode visualizing the heart and great vessels from different directions and in various scanning planes. Results Cardiac anomalies were detected in 173 fetuses, giving an overall incidence of 1 in 210 pregnancies. In 44% of these, the cardiac anomaly was isolated. An abnormal karyotype was detected in 27 of the 72 cases that underwent chromosomal analysis. An abnormal nuchal translucency finding was observed in 59 fetuses. The sonographic diagnosis was confirmed after delivery or at postmortem in 90 cases. Ten fetuses had a cardiac anomaly which differed from the anomaly suggested by sonography. In the remaining cases, a postmortem examination was not possible because termination of pregnancy was performed by dilatation and curettage. In four cases we did not detect the cardiac anomaly in early pregnancy. Two of them were detected at rescanning in mid-pregnancy. Conclusion Early detection of fetal cardiac anomalies is now possible. Most anomalies occur in low-risk pregnancies. We suggest performing a detailed early multidirectional dynamic continuous sweep ultrasound examination of the fetal cardiovascular system in all pregnancies. INTRODUCTION There are at present four concepts guiding the sonographic examination of the fetal heart Fetal echocardiography is difficult to perform and is timeconsuming. 2 Fetal echocardiography should be performed only in selected cases of high-risk pregnancies. 3 The optimal time to perform fetal echocardiography is at weeks gestation. 4 Fetal echocardiography relies mainly on the four-chamber view, the short-axis view and the long-axis view. The present study challenges these concepts and documents our experience regarding these issues. We present a systematic approach to the examination of the normal and abnormal hearts and provide our data on fetal heart scanning in early pregnancy. MATERIALS AND METHODS This study summarizes the data on consecutive fetuses which were evaluated with transvaginal ultrasound at weeks gestation during a study period of 14 years. More than 99% of examinations were performed at weeks gestation. Eighty-three percent of patients were regarded as having low-risk pregnancies. Examinations were performed by two sonographers with ESI 1000 and ESI 3000 ultrasound machines (Elscint Ltd, Haifa, Israel) using 6.5-MHz mechanical and 7.5-MHz annular transvaginal probes. A complete survey of all fetal organs was performed in all cases. During some stage of the examination, which lasts min, the fetus is usually in a position that is ideal for cardiac examination. Once this position has been obtained, a detailed cardiovascular examination is possible. Imaging of the heart does not rely on only still images of the classic views, but is instead performed in a dynamic continuous sweep mode, visualizing the heart in different directions and scanning planes. The four chambers are imaged in two main planes. One comprises a lateral or perpendicular scanning plane (left or right) in which the ultrasound beam is perpendicular to the septum, enabling the symmetry between the ventricles and the contractility of the myocardium to be assessed. In the Correspondence: Dr E. Z. Zimmer, Department of Obstetrics and Gynecology, Rambam Medical Center, Haifa 31096, Israel ( ALKOL@netvision.net.il) Accepted ORIGINAL PAPER

2 second view (a parallel approach), the ultrasound beam is almost parallel to the septum. Scanning may be performed in the posterior anterior direction; however, we have found that the anterior posterior direction is more informative. In this view, the septum and insertion of the atrioventricular (AV) valves is best depicted. Sonographers should be aware that, in order to avoid an acoustic shadow, it is necessary to perform the examination with the smallest insonation angle (to the septum) possible. This view is important for the detection of ventricular septal defects (VSDs) which are larger than the axial resolution but smaller than the lateral resolution. Other major anomalies detected in the four-chamber views are the common AV canal, Ebstein s anomaly and corrected transposition of the great arteries. The insertion of at least two pulmonary veins into the inlet of the left atrium can be imaged from any direction. The image of the outflow tracts refers to the whole course in the mediastinal space occupied by the aorta and a right vessel which consists of the main pulmonary artery in its proximal part and the ductus arteriosus in its distal part. Of note, there is no sonographic marker to define the transition from the pulmonary artery to the ductus arteriosus. The great vessels should be imaged up to the connection of the ductal arch and descending aorta. The preferred way of scanning is to image both great vessels in a continuous and simultaneous mode and follow their course. This will give a good idea regarding the size, shape and location of the vessels, as well as the connected circulation. It is our experience that the best images are obtained while scanning the fetus from the direction of its right shoulder. However, from the left side it is also possible to scan in anterior posterior or posterior anterior directions. The great vessels should be of equal size along their course. Special attention should be paid to three specific images of the vessels that may be described by the letters X, P and Y (Figures 1 and 2). Figure 1 Top: schematic presentation of the normal configuration of the great arteries in the thoracic space. The regions of the X, P and Y views are marked. Middle: superposition of the schematic presentation on autopsy at about 15 weeks gestation. a, aorta; r, right outlet. Bottom: sonographic image of the appropriate regions with (left) and without (right) demarcation. T, trachea (marked by arrowheads); SVC, superior vena cava. Figure 2 Sonographic image (left) and schematic representation (right) of a high transverse P view at 15 weeks gestation. A, aorta; M, main pulmonary artery; D, ductus arteriosus; SVC, superior vena cava; t, trachea; S, spine; MPA, main pulmonary artery; DUCT, ductus arteriosus. Ultrasound in Obstetrics and Gynecology 361

3 Image X In the proximal part of the outflow tract, there is normally continuity between the interventricular septum and the anterior wall of the aorta. The angle between the septum and the anterior wall of the ascending aorta is 135. This image is actually the traditional long-axis view. Absence of this angle is an important marker of an overriding aorta. While depicting this angle, the transducer should be rotated through 90 to the previous plane in order to visualize the main pulmonary artery as it crosses over the aorta. This point of crossing, which can be viewed in any direction (right, left, anterior, posterior or oblique) resembles the letter X (Figure 1). Absence of the X sign and the appearance of parallel vessels is a clue to transposition of the great vessels or double outlet right ventricle. Image P The medial part of the outflow tract is observed in the upper transverse section of the mediastinum. Normally, the right outlet vessel will be depicted as a straight vessel while the aorta resembles an arch in both rostrocaudal and transverse planes. The image obtained resembles an inverted letter P (Figures 1 and 2). These scanning planes may assist in the diagnosis of anomalies such as corrected and non-corrected transposition of the great arteries, interruption of aortic arch, truncus arteriosus, tetralogy of Fallot, left or right hypoplastic ventricles and other rare conditions in which the flow in one of the vessels is diminished. Image Y The distal part of the vessels at the connection point of the aorta and ductus arteriosus provides an ideal place for comparison between blood flow from both sides of the heart and outflow tracts 5. This point resembles the letter Y. Normally, the aorta and ductus arteriosus are of equal size at their connection in early pregnancy, whereas in cases of coarctation of the aorta, the ductus arteriosus is significantly larger 5. While obtaining these views, the relationship between the aorta and trachea should be determined. The trachea is depicted as an echogenic circle near the connection of the aorta and the ductus arteriosus (Figures 1 and 2). This deep paratracheal view will disclose if there is a vascular ring, double aortic arch or right aortic arch 6. Scanning of the large veins is an integral part of the fetal examination. A right sagittal plane will visualize the inferior and superior vena cavae and the ductus venosus. RESULTS The fetal heart examination was completed, in most cases, in the first scanning session. In only < 1% of cases did we fail to image the heart in all directions and patients were rescheduled for a second examination. The common causes for failure were the presence of uterine myomas, fetuses which did not move and whose position did not change sufficiently during the evaluation and multiple pregnancies in which one of the fetuses was positioned out of the optimal scanning zone. Cardiovascular anomalies were detected in 173 fetuses (Table 1). Note that only the main anomaly for each fetus is presented in the table even though some fetuses had several cardiac anomalies. It should also be noted that defects such as a small isolated VSD or valvular stenosis are not reported in the study since the size of the defect might be beyond the resolution limit of current ultrasound machines. Forty-six anomalies (26%) were detected in high-risk pregnancies and 127 (74%) in low-risk pregnancies. Nine cases with anomalies in the low-risk group were referred to us for a second opinion regarding a possible cardiac anomaly. The overall incidence of cardiac anomalies was 1 in 210 pregnancies. The incidence in low-risk pregnancies was 1 in 238 excluding those cases referred for a second opinion. Seventy-seven (44%) fetuses had an isolated cardiovascular anomaly while the other 56% fetuses had associated anomalies. An abnormal fetal karyotype was detected in 27 (37.5%) of 72 patients who underwent amniocentesis. Abnormal nuchal translucency findings were observed in 59 (34%) of the 173 fetuses with a cardiac anomaly; amniocentesis was performed in 31 of these fetuses and 22 (70%) of the fetuses had an abnormal karyotype. Cardiac anomalies detected by imaging the great vessels Most anomalies are detected by finding a discrepancy in size between the right and left outflow tracts. However, sonographers should be aware that until 14 weeks gestation the transverse section of these vessels has a slightly more elliptical rather than a round appearance. After 15 weeks gestation, an elliptical appearance may be observed in a few cases in the right outflow tract. Therefore, the size of the tracts should be Table 1 Cardiovascular anomalies detected in 173 fetuses Anomaly n EWD Tetralogy of Fallot/double outlet right ventricle Hypoplastic left heart Coarctation of aorta Transposition of the great arteries Corrected transposition of the great arteries 5 15 Heart failure* Common AV canal Vascular ring Isolated VSD 9 15 Truncus arteriosus 5 14 Ebstein s anomaly 3 14 Ectopia cordis 3 11 Interruption of IVC 3 15 Hypoplastic right heart 1 15 Single ventricle 2 14 Absent ductus venosus 1 15 ASD as an isolated anomaly 1 16 Aortic aneurysm 1 15 Interruption of aortic arch 1 15 Tricuspid atresia 1 16 EWD, earliest week of detection; AV, atrioventricular; VSD, ventricular septal defect; IVC, inferior vena cava; ASD, atrial septal defect. *Cardiomyopathy, endocardial fibroelastosis, supraventricular tachycardia. 362 Ultrasound in Obstetrics and Gynecology

4 determined in various planes in order to confirm that there is a true discrepancy in size between the vessels. Right outflow tract larger than the left outflow tract In severe cases of discrepancy the whole aorta was constricted and was always associated with a hypoplastic left heart. In extreme cases it was difficult to depict the aorta. For cases in which a discrepancy of more than 50% was noted between the left and right sides in the Y zone, a coarctation of the aorta was diagnosed in the newborns or on postmortem examination when termination of pregnancy was performed. In cases with a smaller discrepancy of 25 50% between the left and right sides, some fetuses had coarctation of the aorta while others had a normal outcome. In those with coarctation of the aorta, the discrepancy remained or had even increased on re-examination at 20 weeks gestation. Fetuses in which the discrepancy in size between vessels decreased in mid-pregnancy usually had a normal cardiovascular examination after delivery. Left outflow tract larger than the right outflow tract The diagnosis in most such cases is tetralogy of Fallot or double outlet right ventricle (Figure 3). In each of our 31 cases of these anomalies, we observed a significant discrepancy between the aorta and pulmonary artery and its continuation to the ductus arteriosus. In fact, we believe that a definite prenatal diagnosis of tetralogy of Fallot is doubtful without this sonographic marker. In our experience, the discrepancy between the vessels is also the most easily depicted and most reliable sonographic finding in cases of tetralogy of Fallot. Another sonographic feature of tetralogy of Fallot is the inability to depict the ductus arteriosus. We observed this phenomenon in about 20% of cases. In severe cases of tetralogy of Fallot, it is difficult to recognize the right outlet and the differential diagnosis of a truncus arteriosus should be considered. Single outflow tract A true single outflow tract was depicted in cases of truncus arteriosus. There are two situations in which a pseudo single outlet vessel can be seen: first, in all cases of corrected or non-corrected transposition of great vessels and some cases of a double outlet right ventricle. In such instances, the P view will disclose only a single vessel in an axial upper mediastinal section because the aorta conceals beneath it the main pulmonary artery (Figure 4). The second situation occurs in cases in which one of the outlet vessels is extremely narrow and is hidden beneath the normal vessel or its size is below the resolution limit of the ultrasound machine, (e.g. severe cases of hypoplastic left ventricle or tetralogy of Fallot). We found simultaneous video imaging of the large vessels to be more important than the four-chamber view in the diagnosis of cardiovascular anomalies (81 vs. 36 cases, respectively). In the remaining fetuses the diagnosis relied on both views. Regarding the accuracy of our prenatal sonographic diagnoses, it should be noted that we admit our patients from all parts of the country and many of them do not deliver in our hospital. We were therefore able to review only 9355 medical charts after labor and delivery or termination of pregnancy. Patients who deliver in other hospitals are requested to inform us about any anomaly detected in the newborns and the compliance is good. However, the fact that we did not personally review all medical records precludes the possibility of giving the precise number of false-negative diagnoses. The sonographic diagnosis was confirmed in 90 cases after delivery or on postmortem examination. In 10 cases a different cardiac anomaly was observed (Table 2). In addition, there were four fetuses in which we did not detect an anomaly in early pregnancy. In one case a common AV canal was found at Table 2 Fetuses for which the final diagnosis was different from the prediction Prediction n Diagnosis Figure 3 Sonographic images with and without demarcation of the vessels (top) and the autopsy finding (bottom) of Tetralogy of Fallot at 15 weeks gestation. A, a very wide aorta; R, a thin right outlet; d, a constricted ductus arteriosus; M, the thin main pulmonary artery. Tetralogy of Fallot 2 Truncus arteriosus Tetralogy of Fallot 2 Pulmonary atresia Truncus arteriosus 3 Tetralogy of Fallot Interruption of aortic arch 1 Severe coarctation of aorta Common AV canal 1 Ventricular septal defect Aortic atresia 1 Severe hypoplasia of aortic arch AV, atrioventricular. Ultrasound in Obstetrics and Gynecology 363

5 Figure 4 Transposition of great arteries (T.G.A) at 15 weeks gestation. The sonographic image (left) of the P view revealed only one vessel (arrow). The autopsy finding (right) shows the upper and anterior aorta marked by arrowheads. The main pulmonary artery (P) was hidden beneath the aorta and was therefore not depicted by ultrasound. 20 weeks gestation. In the second case, endocardial fibroelastosis and hypoplasia of the left ventricle and aorta were observed at 23 weeks gestation. In the other two cases, the anomaly was detected in the newborn; one had transposition of the great vessels and the other had an interrupted aortic arch. Both these latter fetuses were scanned at the beginning of the study period during our learning phase. We regard these cases as errors in diagnosis and not as cases of evolving congenital heart defects. In the remaining cases, it was not possible to confirm the sonographic diagnosis, usually because pregnancy was terminated by dilatation and curettage, which destroys the embryo and does not enable an accurate postmortem examination. DISCUSSION The present study shows that many cardiac anomalies can be detected at the beginning of the second trimester of pregnancy. Most sonographers still perform a detailed fetal heart examination only after 18 weeks gestation despite the fact that most cardiac anomalies are already present at the end of the first trimester of pregnancy. They perform the examination because transabdominal sonography provides good resolution of the fetal heart anatomy at about 20 weeks gestation in patients with an average body habitus. We used the more advanced technique of transvaginal sonography which enables good visualization of the fetal heart earlier in gestation. Transvaginal sonography improves visualization of the fetal heart in various scanning planes due to the fact that the fetal thoracic cage is only slightly ossified in early pregnancy. Transabdominal scanning with this technique is suboptimal. However, because of the ossified fetal ribs in mid-gestation and the maternal abdominal wall, the resolution is decreased and the examination takes more time. Imaging of the outflow tracts is mandatory. Our study confirmed previous reports which have shown that using only the four-chamber view for fetal heart examination is insufficient, as many anomalies may not be detected by observation in this view 7 9. Most sonographers who examine the outflow tracts actually evaluate the proximal parts of the right and left ventricular outflows. Yoo et al. 10,11, in their pioneering works with transabdominal sonography in the second half of pregnancy, extended the examination to include the aortic arch view and the three-vessel view in the upper mediastinum. The three-vessel view demonstrates normal cross-sections of the ascending aorta and superior vena cava and an oblique section of the main pulmonary artery. The concept of our examination is quite similar to the method suggested by Yoo et al. However, in our experience, our approach of evaluating the vessels in a dynamic continuous sweep mode instead of imaging definite still views is more practical and easy to learn. We are aware that our technique of examination may be difficult to understand on first reading. We found that the best way to teach the technique is by using a model so that the sonographer can understand the relationship of the great vessels and the heart. Transvaginal ultrasound examination in early pregnancy offers several important advantages. It preserves the entire spectrum of diagnostic and therapeutic options including genetic studies when indicated or therapeutic abortion upon the parents request. In cases of severe fetal malformations, early detection may prevent unnecessary invasive procedures, such as amniocentesis for advanced maternal age or cervical suture for an incompetent cervix. Furthermore, in cases of termination of pregnancy, it is less dangerous to perform the procedure in early gestation than in mid-gestation. Several investigators have shown that inclusion of a detailed fetal heart examination as a screening examination has a substantial effect on the detection of congenital heart disease 9, However, since most sonographers do not as yet have the skill to perform an accurate diagnosis of fetal cardiac anomalies, a screening policy has not been accepted at most centers. Our study shows that a detailed fetal heart examination is of great value in all pregnancies since most cases of anomalies 364 Ultrasound in Obstetrics and Gynecology

6 are detected in low-risk pregnancies. It is therefore our belief that the cardiovascular examination should be an integral part of each sonographic survey of fetal organs. Pregnant women should be informed that the risk of a major cardiac anomaly is 1 in 238 low-risk pregnancies. Furthermore, it has already been shown that the chance of neonatal mortality decreases in cases with a prenatal diagnosis of a cardiac anomaly 3,4,16. The technique of scanning the heart is easy to learn for sonographers who are familiar with both transabdominal and transvaginal scanning. We believe that depiction of the heart anatomy is easier in early pregnancy compared with advanced gestation. There are reports on several severe cardiac anomalies which may evolve in utero later in pregnancy These anomalies are mainly related to major vessels and critical outlet stenosis. However, most of these cases are very rare and have been observed at the end of the second trimester or during the third trimester. Postponing the fetal heart examination to weeks gestation will therefore not improve our ability to detect these anomalies. As already noted, we had only two cases in which our initial scan in early pregnancy was judged to be normal and the heart anomaly was detected on rescanning the patients in mid-pregnancy. In summary, transvaginal sonography and the technique of dynamic continuous sweep imaging of the cardiovascular system now enable an accurate diagnosis of severe fetal cardiac anomalies in early pregnancy. Most of these anomalies are detected in low-risk pregnancies. The technique of scanning is not difficult to learn and sonographers can adopt it in a short time period of a few months. It is therefore our belief that in the future an early detailed fetal cardiac examination should be performed in all pregnant women. REFERENCES 1 Buskins E, Steyerberg EW, Hess J, Wladimiroff JW, Grobbee DE. Routine prenatal screening for congenital heart disease: What can be expected? 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