Distinguishing Right From Left: A Standardized Technique for Fetal Echocardiography

Distinguishing Right From Left: A Standardized Technique for Fetal Echocardiography Timothy M. Cordes, MD, Patrick W. O'Leary, MD, James B. Seward, MD, and Donald J. Hagler, MD, Rochester, Minnesota Improved echocardiographic equipment and increasing experience have led to accurate and reliable prenatal diagnosis of congenital defects and arrhythmias. However, without a standard convention for acquisition and presentation of fetal images, distinguishing the right side of the fetus from the left side can be difficult and confusing. This article proposes a standard method of image acquisition and presentation that allows confident determination of the fetal right/left axis by easily identified anatomic landmarks. This technique provides a reliable determination of the fetal right/left axis regardless of fetal position (i.e., face up, face down, facing left, or facing right), in both real time and retrospective review. Only after the fetal right/left axis has been determined can accurate diagnoses of fetal atrial and visceral situs, base-apex axis, and cardiac segmental anatomy be made. ( J AM Soc EcHOCARDIOGR 1994;7:47-53.) Feta! echocardiography has become a sensitive and reliable tool for prenatal diagnosis ofcongenital heart defects and arrhythmias. J.4 Advances in ultrasound technology have led to better resolution and increased diagnostic accuracy. The ability to manipulate image orientation electronically makes it possible to perform a study that closely approximates standard transthoracic echocardiography. There have been several excellent review articles describing recommended techniques and images required for a standard fetal echocardiogram. s-s However, there are important pitfalls encountered in fetal echocardiography, especially relating to complex congenital heart disease. One of the greatest challenges in fetal echocardiography is the constantly variable fetal position within the uterus. As a result, the process of determining the fetal right/left axis (e.g., distinguishing the right side of the fetus from the left side) can be confusing. Variability among echocardiographers re- garding image acquisition and electronic screen manipulation adds to this confusion. This is an important problem because all subsequent cardiovascular diagnoses depend on an accurate understanding of the fetal right/left axis. Ifthere is confusion regarding the right/left axis, then atrial and visceral situs, cardiac position, and cardiac segmental anatomy cannot be evaluated correctly. Also, without a standard method of acquiring fetal images, it is impossible for someone reviewing a recorded study to define the fetal right/left axis. In this report a convention is proposed for acquisition of fetal images that improves the reliability of determining fetal right/left axis. This convention provides a method for confident assignment of right/left axis during the study and retrospective review. This standardized method of examination and image orientation has decreased confusion significantly regarding fetal right/left axis and segmental anatomy at our institution. This technique is described below. From the Divisions of Pediatric Cardiology and Cardiovascular Disease and Medicine, Mayo Graduate School ofmedicine, Mayo Foundation. Reprint requests: Donald J. Hagler, MD, Mayo Clinic, 200 First St. S.W., Rochester, MN 55902. Copyright 1994 by the American Society ofechocardiography. 0894-7317/94 $1.00 +.10 27/l/50619 TECHNIQUE Step 1: Transducer Orientation The examination is begun by setting the echocardiography video screen in the noninverted orientation. The left/right screen format may be set according to 47

48 Cordes et a!. Journal of the American Society of Echocardiography January-February 1994 Figure 1 Drawing and still-frame photograph offetal echocardiographic image demonstrates sagittal view. Drawing (A) and echocardiographic image (B) show fetus lying face up. Drawing (C) and echocardiographic image (D) show fetus lying face down. Transducer is oriented so that fetal head is to right side of video screen. Fetal anterior (A) /posterior (P), superior (S) I inferior (I), and left (L) I right (R) axis' are identified. DAo, Descending aorta. the echocardiographer's preference. However, once opposite side of the transducer will be displayed on the screen has been set it should not be electronically the left side of the video screen. This is equivalent "switched" until after determination ofthe segmental to the standard display for transthoracic, echocardioanatomy. The fetal head and sagittal plane of fetal graphic short-axis scans. The fetal transverse image body are then located. The transducer is oriented so thus acquired is presented in the caudal-to-cranial that it is parallel to the fetal sagittal plane, with the perspective. fetal head on the right side ofthe video screen (Figure l). When the transducer is aligned parallel to the Step 2: Determining Fetal Right/Left Axis fetal cranial-caudal axis this way, the side ofthe transducer toward the fetal head can be designated the image is acquired as described above, the ultrasound When the fetus is lying face up and the transverse "top" of the transducer. The transducer is then rotated clockwise (from the perspective of the echo In this transverse image the fetus' left side is on the beam passes through the fetal anterior chest wall first. cardiographer) 90 degrees, to visualize optimally a right of the video screen, and the fetus' right side is transverse image of the fetal thorax. This maneuver ensures that images scanned from the designated "top" of the transducer will be dis aging with left-sided structures on the right of the played on the right side ofthe video screen from the video screen. Ifthe fetus is face down, the ultrasound operator's perspective, and images scanned from the beam passes through the back of the fetus first. The on the left ofthe video screen. This format is identical to the usual image format for short-axis cardiac im

Volume 7 Number l Cordes et al. 49 Figure 2 Schematic drawing of fetal trunk as viewed in transverse plane on video display. When view is obtained as described in text, it is displayed from caudal to cranial perspective. With fetal spine used as landmark, right and left sides of fetus can be determined. Relationship of right and left sides of fetus and spine are constant despite fetal rotation from face up (bottom), right side up (left), face down (top), and left side up (right). L, Left; R, right; P, posterior. transverse image in this setting will be the inverse of the standard precordial presentation and the fetus' left side will be on the left of the video screen. p If the fetus is lying on its side and its left side is up (directed toward the maternal anterior abdominal wall), when viewed echocardiographically in the transverse image plane, the back of the fetus will be to the right side of the video screen. This is true regardless of the direction of the fetal cranial-caudal axis within the uterus. Thus during a routine fetal echocardiographic examination, if the transverse images demonstrate the back of the fetus on the right of the video screen, the left side of the fetus will be up (directed to the mother's anterior). If the fetus is lying with its right side up, the transverse images would show the back of the fetus on the left of the video screen. Figure 2 illustrates the fetal transverse images and the right, left, and posterior references as the fetus rotates 360 degrees around its caudalcranial axis. This method orients the image based on the fetal position rather than maternal position and uses relatively fixed fetal anatomic landmarks (i.e., the spine Figure 3 Transverse image of fetal abdomen demonstrates situs solitus ofviscera. Fetus is lying with right side up. Liver (L) is toward top ofvideo screen, corresponding to right side of fetus, and stomach (S) is on left side of fetus. *Spine; DV, ductus venosus. and head). Orienting the fetal sagittal plane and subsequent transverse plane as described above allows image interpretation based on known ultrasound physics and electronic imaging standards. These landmarks can then form the cornerstone for complete segmental echocardiographic diagnosis. When the image is acquired in this way the fetal rightileft axis can be confidently defined regardless of the fetus' position within the uterus. To illustrate how this method can be applied, let us consider the determination of fetal visceral situs and cardiac position. Visceral situs. The major visceral landmarks available in fetal echocardiography are the liver and stomach. These structures and their relative positions are demonstrated reliably in the transverse image during fetal echocardiographic evaluation. In situs solitus, if the fetus is lying face up, the liver will be seen to the left of the video screen and the stomach to the right. With situs inversus ofthe viscera, the liver will be to the right of the video screen and the stomach to the left. When the fetus is face down, the liver is seen to the right of the video screen in visceral situs solitus and to left of the video screen in situs inversus. If the fetus is lying with its back to the right of the video screen we know that the left side is to the top of the video screen. Therefore the liver will be toward the bottom ofthe video screen in situs solitus and to the top of the screen in situs inversus. When the back of the fetus is to the left, the fetus' right

50 Cordes et al. Journal of the American Society of Echocardiography January-February 1994 Figure 4 A, Drawing represents echocardiographic transverse image of fetal thorax. Top drawing demonstrates levocardia; bottom drawing reveals dextrocardia. B, Echocardiographic image shows transverse view of fetus lying face up with levocardia. Image (C) demonstrates dextrocardia in fetus with complex congenital heart disease, lying face up. CA, Common atrium; V, ventricle; *spine. Table 1 Situs solitus of the viscera (transverse view) Fetal position Screen orientation Face up Liver on left Stomach on right Face down Liver on right Stomach on left Left side up Liver at bottom, back to right Stomach at top Right side up Liver at top, back to left Stomach at bottom side is to the top of the screen. Thus in situs solitus the liver is toward the top ofthe video screen (Figure 3) and in situs inversus it is toward the bottom of the video screen. Table l outlines the video positions ofthe liver and stomach in visceral situs solitus. Table 2 describes the video screen image in visceral situs mversus. Cardiac situs: levocardia and dextrocardia. When a fetus with levocardia is lying face up and the transverse image is obtained as described above, the cardiac apex will point toward the right ofthe screen. In the case ofdextrocardia, the apex will point to the left ofthe video screen (Figure 4). Ifthe fetus is lying face down and there is levocardia, the cardiac apex will point toward the left of the screen. With dextrocardia and a fetus lying face down, the cardiac apex will be toward the right of the screen (Figure 5).

Volume 7 Number l Cordes et al. 51 A Figure 5 A, Drawing of levocardia (top) and dextrocardia (bottom) as seen from transverse view when fetus is lying face down. B, Corresponding echocardiographic image with levocardia. *Spine. Table 2 Situs inversus of the viscera (transverse view) Fetal position Screen orientation Face up Liver on right Stomach on left Face down Liver on left Stomach on right Left side up Liver at top, back to right Stomach at bottom Right side up Liver at bottom, back to left Stomach at top As mentioned previously, when the fetus is lying with its back to the right of the video screen, the left side ofthe fetus is seen at the top ofthe video screen, and levocardia will be evident by the cardiac apex directed toward the top ofthe screen. Therefore with dextrocardia the cardiac apex will be to the bottom of the video screen (Figure 6). If the fetus is lying on its side with its back to the left ofthe video screen, its right side will be at the top of the video image and the left side will be down. Therefore with levocardia the cardiac apex will point toward the bottom of the video screen, and in dextrocardia it will point toward the top of the video screen (Figure 7). It is evident that the key in defining visceral situs and cardiac position is based on confident determination of the right and left sides of the fetus. Knowing the right/left axis will also provide the orientation to determine atrial situs and atrioventricular and ventricular-great artery relationships. The echocardiographic method for defining atrial and ventricular segmental anatomy has been described previously and can be applied here. 9 10 METHODS Since February 1992, we have routinely used this technique during all fetal echocardiograms. One hundred eighteen complete examinations were performed on 93 fetuses. Each study was performed initially by a fetal ultrasonographer or pediatric cardiology fellow. The studies began with determination ofthe right and left sides ofthe fetus as described above, followed by routine complete fetal echocardiographic studies. Studies were recorded on videotape. Each study was reviewed by an experienced physician (P.W.O., J.B.S., or D.J.H.). The impression of right and left sidedness, visceral and cardiac situs, and segmental anatomy obtained from videotape review was always confirmed by the reviewing physician with additional real-time echocardiographic imaging. Follow-up chart review was conducted on those pregnancies that were followed up or delivered at our institution. Physical examination data at birth was reviewed, as well as chest x-ray data, echocar

52 Cordes et al. January-February 1994 Left side up Levocardia A left side up Dextrocardia Figure 6 A, Drawing of transverse images obtained with left side of fetus up. Levocardia is shown in top drawing; dextrocardia is demonstrated in the bottom drawing. Echocardiographic image (B) demonstrates levocardia as seen in transverse view with fetus' left side up. *Spine. Right side up Levocardia Right Si«re uo Dextrocardia Figure 7 A, Drawings of transverse images of fetal thorax with fetus lying right side up. Top drawing shows levocardia; bottom drawing shows dextrocardia. Corresponding echocardiographic image (B) in fetus with levocardia. *Spine. agreed with the diagnosis based on videotape review. This diagnosis was also confirmed with subsequent real-time imaging by the reviewing physician in all cases. Of the 93 fetuses studied, 55 were followed up at our institution, 29 were being followed up or deliv ered elsewhere, and nine had not yet been delivered. In the 55 fetuses that were eventually delivered at diagram, and postrnortum examination when available. RESULTS In all 93 fetuses the initial determination ofright and left sidedness, visceral and atrial situs, ventricular position, and ventricular-great artery relationship

Volume 7 Nurn!Jer 1 Cordes et al. 53 our institution, follow-up demonstrated agreement with the fetal echocardiogram determination of visceral and atrial situs, cardiac position, and intracardiac segmental relationships in all cases. DISCUSSION We have described a technique that allows accurate and reproducible determination of fetal right/left axis. This method also allows confident determination of right/left axis during review of a videotaped fetal examination. The k<:y steps to this technique are orientation of the fetal sagittal plane with the head to the right ofthe video screen and then a 90-degree clockwise transducer rotation to obtain the transverse image. This results in a transverse image presented in the standard caudal to cranial perspective. Reversal of either one of these steps or electronic left/right screen inversion will confound the determination of the fetal right/left axis. Once the fetal right/left axis is assigned accurately, the correct diagnoses of visceral and atrial situs, cardiac position, and cardiac segmental anatomy can be made. Once this has been done, the cardiac image can be formatted electronically to conform to standard precordial views. To reverse this sequence (e.g., to conform to standard image orientation before determining fetal right/left axis) can lead to significant errors in interpreting fetal cardiac anatomy. Fetal echocardiography has become an extremely valuable prenatal and perinatal diagnostic tool. Confusion about the fetal right/left axis can still occur. If confusion regarding right/left axis is present, cardiac segmental relationships cannot be described ac- curately. This confusion can be reduced if a standardized approach is used to distinguish the right side from the left side of the fetus. Therefore, we recommend that the standardized method of image acquisition and video presentation described in this article be used routinely for fetal echocardiography. REFERENCES l. Allan L, Crawford D, Handerson R, et a!. Spectrum of congenital heart disease detected echocardiographically in prenatal life. Br Heart J 1985;54:523-6. 2. Kleinman C, Weinstein E, Talner N, eta!. Echocardiography: applications and limitations. Ultrasound Med Bioi 1984; 10:747-55. 3. Allan L. A review of fetal echocardiography. Echocardiography 1985;2:351-76. 4. Santulli T. Fetal echocardiography: assessment of cardiovascular anatomy and function. Clio Perinatol1990;17:9ll-40. 5. Devore G. The prenatal diagnosis ofcongenital heart disease: a practical approach for the fetal sonographer. J Clio Ultrasound 1985;13:229-45. 6. Silverman N, Golbus M. Echocardiographic techniques for assessing normal and abnormal fetal cardiac anatomy. JAm Coli Cardia! 1985;5:20S-9S. 7. Cyr D, Guntheroth W, Mack L, eta!. A systematic approach to fetal echocardiography using real-time/two-dimensional sonography. J Ultrasound Med 1986;5:343-50. 8. Reed K. Fetal echocardiography. Semin Ultrasound CT MR 1991;12:2-10. 9. Huhta], Hagler D, Seward], eta!. Two-dimensional echocardiographic assessment of dextrocardia: a segmental approach. Am J Cardiol1982;50:1351-60. 10. Hagler D, Tajik A, Seward], eta!. Atrioventricular and ventricular great artery discordance (corrected transposition of the great arteries): wide angle two-dimensional echocardiographic assessment ofventricular morphology. Mayo Clio Pro 1981;56:591-600.