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Fetal cardiac screening in midgestation
- 1. FETAL CARDIAC SCREENING IN MIDGESTATION Assoc. Prof. Dr. Başak Baksu Perinatology, Acibadem Kozyatagi Hospital, İstanbul, Turkey
- 2. OUTLINE • Importance ? • Updated guideline recommendations: standard view ? what else ? • Technique and technical issues
- 3. WHY BOTHER ? Cardiac defects 1o fetal anomaly: 8-9 /1000 live births ↑ morbidity – mortality: 35 % of infant deaths from congenital malformations Majority in low-risk groups (80%) Only detected by routine screening Achiron R et al. 1992 Allan LD. 200 Devine PC, et al. 2000 Lindsay LD. 1994 Todros T. 2000
- 4. SCREENING SERVES: Increased prenatal diagnosis improves survival and morbidity allows parental counselling
- 5. GENERAL CONSIDERATIONS • Detail of anatomical assessment of CHD is NOT NEEDED • Essential is to say ‘THE HEART LOOKS NORMAL’ • Simple, solid KNOWLEDGE BASE is essential • Learning requires certain TRAINING
- 6. AIMS Define normality: evalute form and function Identify those suspicious / abnormal Referral for fetal echocardiography
- 7. FETAL HEART SCREENING VIEWS • Four Chamber View + Outflow Tract Views: routine screening evidence-based recommended ISUOG 2013, AIUM 2013 • Being familiar with 3 Vessel View and 3 Vessel Trachea View: is desirable should be attempted ISUOG 2013 • Color flow Doppler: can be used, if the operator feels competent ISUOG 2013
- 8. WHY 4CV + OUTLOW TRACTS ? • Wide variation in DR EUROCAT Study 2001 • DR increases with 4CV + OFTs: Achiron R, 1992 DeVore GR. 1998 Jaeggi ET. 2001 LESS EXPERIENCED (%) EXPERIENCED (%) 4CV 20 45-60 4CV + Outflow 50 80
- 9. Skill & Experience Difficulty of maintaining alertness in low-risk group Obesity Scars GA (18-22 GW) AFV Position Movements Tegnander E, et al. 2006 Quartermain MD, et al. 2015 ISUOG 2013
- 10. ELEMENTS TO BE DETERMINED AT THE ONSET OF THE SCAN • Position • Size • Axis • Rate & Rhytm • Number • Position & Laterality • Abdominal Situs • Fetal Biometry FETUS HEART
- 11. POSITION & LATERALITY How does the fetus lie in uterus ? Orientation of the fetal spine ? What is the presenting part ? Establish laterality: • handheld doll model • Right hand rule of thumb
- 12. RIGHT HAND RULE OF THUMB Bronshtein MI, Gover A,Zimmer EZ. Sonographic definition of the fetal situs. Obstet Gynecol 2002; 99: 1129-30 Always fetal left side Fetal head Fetal abdomen
- 14. Transverse view of the abdomen, beneath the level of the diaphragm ABDOMINAL SITUS Liver
- 15. SITUS SOLITUS • 4CV • stomach + heart + dAo both on the left • cardiac axis to the left • LA and dAo nearest to the spine • RV nearest to sternum
- 16. FETAL BIOMETRY • Biometry: GA ? • No of vessels in the umbilical cord: 2 UA and 1 UV
- 17. Almost parallel RV most anterior Aortic arch most superior 20 GW HEART
- 18. CARDIAC POSITION • 4CV • bulk of the heart: left chest • 2/3 of heart: anterior chest R L Sp dAo
- 19. CARDIAC SIZE • Area of heart: 1/3 of area of thorax Cardiothorasic index: 1/3 • Circumference of heart/thorax : ½ • No pericardial effusion (< 2 mm )
- 20. CARDIAC AXIS Angle of the fetal heart 45 ± 20 o 45 o
- 21. RHYTHM & RATE 120 – 160 beats/min Should beat rhythmicly All chambers should contact simultaneously
- 22. TECHNICAL CONSIDERATIONS • ↑ f transducer: 5 Mhz • Cross-sectional gray- scale • B-mode ± color Doppler • ↑ frame rate • ↑ contrast • ↑ resolution • Low persistence • A single acoustic focal zone • Narrow image field (25-300) • Harmonic imaging • Zoom • Cine-loop
- 23. OPTIMIZE YOUR IMAGE Resort to echocardiography setting Enchanced image contrast Enchanced tissue characterization Faster frame rate Minimize depth Insonate heart Adjust focal zone Zoom
- 25. ATRIUMS & ATRIAL SEPTUM Septum primum should be (+), near crux Two atria ≈ in size RA: Anterior Anterior to right of LA LA: Anterior to spine Posterior Receives pulm.veins Pulmonary veins Septum primum FO flap Crux Foramen ovaleFO flap opens to LA
- 26. Almost same size No hypertrophy Intact IVS (from apex to crux) VENTRICULES AV VALVES LV: Fine trabeculation Smooth walls Uniform thickness Conical shape Longer MV inserts to free walls RV: Coarse trabeculation Moderator band Makes apex Crescent shape Shorter Off-set of TV TV attaches to IVS AV valves : move freely not thickened off-set (+)
- 27. OUTFLOW TRACT VIEWS Normality of great vessels: • connections to the appropriate ventricules • relative size • position • adequate opening of the arterial valves Normal ‘cross-over’
- 29. SWEEP TECHNIQUE
- 31. LEFT VENTRICULAR OUTFLOW TRACT RV anterior to LVOT LA posterior to LVOT Continuity of IVS with aorta AV should move freely AV should not be thickened Anterior Posterior
- 32. RIGHT VENTRICULAR OUTFLOW TRACT MPA anterior and to left of aorta Continue distally towards left SVC can be seen Take-off of RPA PV should move freely PV should not be thickened
- 33. 3 VESSEL VIEW
- 34. 3 VESSEL VIEW From left anterior to right posterior: Size: mPA > aAo > SVC Alingment: Straight Number Size Alignment Arrangement Pulmonary artery Aorta dAo SVC
- 35. 3 VESSEL TRACHEA VIEW
- 36. 3 VESSEL TRACHEA VIEW aAo running anterior to trachea Both arches left of trachea ‘V-shape’ connection of arches Ductal arch Aortic arch SVC Trachea
- 37. COLOR DOPPLER FLOW • Highlights abnormal blood flow patterns • Better visualization in obese • Optimal settings: Narrow color box Appropriate PRF ↓ color persistence Adequate gain
- 38. SUMMARY Number Biometry No of UC vessels Visceral situs Position Size Axis Rhytm & Rate Atria Ventricules Valves Great Vessels FETAL HEART SEGMENTAL ANALYSIS TAV 4CV LVOT RVOT 3VV 3VT STANDART DESIRED COLOR DOPPLER FLOW CONFIDENT
Editor's Notes
- I would like to thank the organization committe for giving me this opportunity to be here today. The topic of my presentation is : fetal cardiac screening during midgestation. Screening of the heart is a critical moment in fetal US and it is one of the most important techniques requiring both skill and experience. Some of you would ask yourselves why bother ? But I hope to convince you how a vital contribution one can make to a the life of a newborn by only doing small movements of the probe in a very short time. starting from a standard obstetric US view Actually, it is seems challenging in the beginning, but once you get the grip of it, it can actually be ‘fun’.
- Starting from the mid-80s, routine obstetrical screening for fetal cardiac abnormalities became well accepted and it remains a standard today. During my presentation I will point out Why it is important ? What the updated obstetric guideline recommendations are for routine cardiac screening during the second trimester ? Which views are standard ? Which views are desired to be obtained ? If the practioner feels confident, what she or he may also use? We will go through the technique and review the technical issues.
- Cardiac defects are the most common fetal structural anomaly: They are 8 times more common than spina bifida And 4 times more common than DS CHD occurs in approx. 8-9/1,000 live births and ass. with significant morbidity and mortality. 35% of infant deaths from congenital malformations are due to cardiovascular anomalies Unfortunately, majority occur in low-risk groups with no identified risk factors and will only be detected by screening at the time of obstetric ultrasound scans. Therefore, prenatal screening for CHD based on the presence of risk factors alone is not very effective, and screening of low-risk pregnancies is important for increasing the percentage of cases diagnosed prenatally.
- It is true that there is limited ability to treat most forms of CHD prenatally. Although termination of pregnancy is not inappropriate for the most complex forms of CHD, this is not the main objective of the detection of CHD in the fetus. In many forms of major CHD, the newborn needs early or immediate resuscitation, with cardiac or ventilator support after birth. In these cases, prior knowledge of the defect and delivery as close as possible to the site of surgical repair, will offer the neonate the best chance of a good result in terms of morbidity and mortality. The diagnosis of severe cardiac malformations prenatally may prevent postnatal hemodynamic decompensation, identify candidates for fetal cardiac intervention lead to better preoperative condition, and potentially result in better overall survival and neurodevelopmental outcome Moreover, prenatal diagnosis of life-threatening forms of CHD, will allow parental choice and preparation.
- While screening of the CHD is one of the most important techniques of prenatal US: It is not necessary to have the level of knowledge of a pediatric cardiologist to perform this systematic prenatal check-up and A detail of anatomical assessment of the CHD is not needed. What is “essential” is to be able to say that a fetal heart looks normal by checking for simple warning signs, rather than being able to precisely diagnose all types of pathologies. But it is essential to acquire a simple, solid knowledge base If we are to carry out fetal heart examinations that are valid and have a long-term prognostic value, Learning the technique for obtaining the images in sufficient quality still requires certain training
- The US practitioner has several aims: to define normality and decide whether there is deviation from normality, by evaluation of form and function in other words: to detect the fetuses with possibility of having CHD requiring referral for further evaluation with fetal echocardiography. however, the order in which structures are assessed will vary from patient to patient. A mental checklist, therefore, is of utmost importance for the operator, so as not to miss important elements of the examination Each patient is a challenge, and each is approached in a slightly different manner with the objective of mentally reconstructing the various pieces of imaging data into a comprehensive, logical picture that portrays the cardiovascular state.
- The fetal heart is the most difficult anatomic structure to appropriately image during a 2nd trimester US examination In 1991, a 4-chamber cardiac view of the fetal heart was added to the anatomic survey. By 2003 the anatomic survey had expanded to include the outflow tracts "if technically feasible". In 2013, the outflow tracts became part of the anatomic survey: evidence-based and recommended by major speciality organizations. ISUOG, AIUM Although this is an important advancement for prenatal screening programs, it remains unclear whether the skill to perform these views is consistently present among doctors at the community level. Being familiar with 3V and 3VT views is desirable and should be attempted Although the use of color flow Doppler is not considered mandatory in these guidelines, Color Doppler imaging can also be used during routine screening, if the operator feels competent with its use.
- There is wide variation in DRs: The EUROCAT study demonstrated a wide variation in DRs throughout Europe, with higher DRs in those countries with an organized policy for US examination of the fetal anatomy at least once during pregnancy A very recent study from US where variability in DR of CHDs has not been evaluated before: They reviewed records of 31,374 infants who had heart surgery at age ≤ 6 months between 2006-2013 US, the DR was only 34 %. During the study period, they mostly used 4CV. DR increases when OTFs is included in the screening. Of course, experience also makes a difference: low sensitivity for screening for CHD by examiners with minimal experience using the four-chamber view When experienced investigators performed screening exams with both 4CV and OTVs, the DR was much higher.
- Variations in DR depends on: Sonographer, mother and fetus. US is operator dependent: It depends on the skill and experience of the individual performing the exam. (experienced: > 2,000 routine 2.trim. US examinations) Although better equipment improved the success in obtaining cardiac view, sonographer experience was more important in the detection of malformations. There is difficulty of maintaining alertness for anomalies of all types, when checking every system in the low-risk population even with experienced physcians using 4CV, esp. when isolated heart disease. FETUS Doing a sonogram and looking at the heart in the fetus is much more difficult not only because of size but also because of the fact that the fetus frequently doesn't hold still
- There are elements which should be determined at the onset of the scan before going futher into the heart.
- First: establish fetal number Since the conventional US image is 2-dimentional in nature, the side of the image depends on the probe direction and position of the fetüs can not be interpreted from the 2D image itself. Hence, the side of the fetal heart has to be defined at the beginning of the exam. Unlike pediatric or adult patients, the fetus cannot be placed in a standard position, nor can the heart be approached consistently from routine angles The first step in obtaining cardiac views is to establish fetal lie that is to determine how the fetus is oriented within the uterus. Determine whether the fetal spine is parallel or transverse to the maternal spine. If both are parallel, longitudinal lie. If perpendicular, transverse lie Define within the uterus the presentation of the fetus: generally vertex or breech. It can be difficult to determine abdominal situs in other presentations like transverse or oblique. But principles to determine situs are the same. To help understanding the position of the fetus, we can make use of a handheld doll model or the right–hand rule of thumb can reliably determine fetal situs during TA scan.
- The right hand rule of thumb is first established by Brochstein. The right hand is held in a fist with the outstreched thumb. With this simple approach, the palm of the right hand corresponds to the fetal abdomen (anterior aspect of the fetus), the dorsal side of the forearm (hand) corresponds to the fetal back (posterior aspect of the fetus), and the fist corresponds to the fetal head. The direction of the outstreched thumb always corresponds to the left side of the fetus regardless of the fetal position. Let’s look at a breech presentation with the fetus positioned face up with spine posterior.
- The US scan plane is from top to bottom with maternal abdomen on the top of the screen Using the right hand thumb rule, the fetal left side should appears on the right side of the screen
- Once fetal left and right sides are confirmed, then abdominal situs cashould be determined. Situs refers to the right and left orientation of fetal organs: it is important to determine whether abd. situs is normal because CHDs are frequently ass. with abnormal abd. situs Looking at the transverse view of the abd. beneath the level of the diaphragm, positions of abd. organs are determined: dAo (normally to the left of the spine) IVC (normally anterior and to the right of the spine) stomach (normally on the left) liver (normally on the right)
- To confirm the normal positions of fetal organs, we have to look at the thoracs as well. Only then we are able to say that that there is a normal left to right axis arrangements in the fetus . Situs solitus describes the normal position of fetal organs: After the transverse abd. view , a sweep towards the fetal head is performed. Then, we reach 4CV. We ascertain if fetal heart and stomach are both on the left side LA and dAo are nearest to the spine cardiac axis points to the left RV is the most anterior part, nearest to the anterior chest
- Before assessment of the heart, measures of fetal biometry (e.g., BPD, HC,FL) are obtained to determine fetal growth. An evaluation of the no of vessels in the umbilical cord should be performed with confirmation of the normal presence of 2 arteries and a single UV
- Here is how small the size of a 20 gestational weeks fetal heart is During fetal life, the heart is most parallel to the ground aortic arch most superior part RV is the most anterior part making the apex of the fetal heart
- Still looking at the 4CV, next we determine how the heart is positioned within the thorax. In this correct orientation, the LA will be located closest to the fetal spine and the RV will be nearest the anterior chest wall. Abnormal axis increases risk of cardiac malformations, esp. outflow tract which usu. accompanies chromosomal anomalies
- Still looking at the 4CV, the size of the heart in relation to the chest cavity is evaluated From a quick visual sense of the image, one should normally be able to fit 3 hearts into the chest cavity in a transverse view. Pericardium is best evaluated at the level of AV valves. There should be no pericardial effusion but small rim of hypoechogenic area around the heart: normal < 2 mm Abnormal displacement from anterior left position can be due to fetal lung hypoplasia, aplasia, diagragmatik herni, space occcupying lesion, gastroschisis, omphalocel
- The angle of the fetal heart relative to midline is normally 45 plus or minus 20 degrees. In other words, a line traversing the IVS will fall between 45 plus or minus 20 degrees leftward from a line extending between the spine and the mid anterior chest wall. Even if 4CV is not satisfactory, size and axis can still be evaluated and serious anomalies can be suspected: Abnormal axis increases risk of cardiac malformations, esp. outflow tract which usu. accompanies chromosomal anomalies Abnormal displacement from anterior left position can be due to fetal lung hypoplasia, aplasia, diagragmatik herni, space occcupying lesion, gastroschisis, omphalocel
- Finally, normal heart rate and rhythm should be confirmed. The heart should beat ritmikly All ventriculles and atrias should contact simultaneously with heart rate of 120-160 beats per sec. FHR 120-160: These elements of the examination are to be determined at the onset of the scan before proceeding any further.
- High f transducer: F effects beam shape and so has major influence of lateral resolution. Higher the f better the lateral resolution but ↓acustic penetration.. Cross sectional gray scale is the basis B mode (brightness) High frame rate: is desireable for fast moving structures. High frame rate dictates reduction in the no of scan lines contributing to each image frame, so a reduction in tissue depth. High resolution: ability to delineate betw. 2 objects Low persistence: Frame averaging, or persistence, are similar functions in which multiple image frames are combined, or “averaged” into a single image. Its effect is similar to that of Speckle Reduction, in which the image appears smoother and noise is reduced in the image A single acoustic focal zone: provides best lateral resolutionI. f you use more than one focus, you decrease frame rate Narrow image field: In US lateral resolution is more limiting aspect of spatial resolution: lateral resolution is limited by beam width in the plane of the reflectors being resolved whereas axial resolution is limited by the length of the pulse. Reflectors closer to one another than the beam width can not be resolved. So, the narrower the beam width the better the lateral resolution. Lateral resolution is highly dependent of tissue depth since the beam width may vary widely with distance along the beam path. Lateral resolution will be at its best in the focal plane of the transducer. Harmonics imaging allows the US to identify body tissue and reduce artifact in the image. It does this by sending and receiving signals at two different US frequencies. Esp. useful in obese. Zoom: Images should be magnified until the heart fills at least one third to one half of the screen Cine-loop: should be used to assist real-time evaluation of normal cardiac structures, like valve leaflets.
- Adequate imaging is essential for accurate screening First step: resort to the echocardiography setting which allows: enchanced image contrast and enchanced tissue characterization faster frame rate Then minimize the depth on the display monitor, start with higher depth, decrease depth to put area of interest at ¾ depth of screen, leave a small area behind to observe useful artifacts like shadowing, enchancement Insonate the heart through an angle that avoids shadowing by the fetal ribs and sternum Adjust the focal zones to the level of point of interest. Focal zone provides best lateral resolution. And then zoom in to magnify area of interest A bigger image allows visualization of details within the heart
- The anatomical structures that should be checked in 4CV are: To define normality, the atria, ventricules and Avs should be evaluated seperately.
- LA: PVs entering LA at least two of these can be seen.. Visualization is recommended Foramen ovale distrupts the continuity of the interatrial septum Septum primum is the lower rim of the atrial septal tissue. It should be present. Septum primum forms part of the normal ‘crux’, . Crux is the point where septum primum meets upper part of IVS and where the AVs insert.
- RV has coarse trabeculation. esp. towards the apex. The distinguishing feature is the presence of the Moderator band which is a thickened trabeculae extending from the septum to the parietal wall of the RV. Moderator band makes the apex of the heart and plays a key role in the electrophysiological conduction of the RV's free wall Due to this interior structure ,RV is crescent in shape and it is shorter than LV. Another impt. feature is the more apical attachment of the TV called as off-set. TV attaches to the IVS and also the RV wall receives direct chordae tendineae insertions This is in contast to its corresponding part in the LV. (in contrast to the papillary muscles of the mitral valve, which do not). LV: Fine trabeculation Smooth walls Uniform thickness Conical shape MV inserts to free walls 2 prominent papillary muscle that inserts into the free wall No direct chordae tendinea insertions to Wall
- We ascertain normality of the great vessels: that are aorta and MPA When this cannot be confirmed, further evaluation is recommended. At the very least, examination of the OFTs requires that the great vessels are appr. = in size and cross each other at right angles from their origins as they exit from their respective ventricules: normal cross-over.
- This is the normal alignment of the fetal heart showing the 4CV with respective chambers and major valve anatomy. Blood leaves the RA and enters the RV via the TV. Most of the blood entering the RA is directed towards the LA thorough FO. Blood entering the LA leaves the LA and enters the LV via MV. Note the direction of flow from the RV to the MPA (RVOT) from right to left. Blood bypasses the lungs via DA that connects to the dAo after the aortic arch gives of the main head and neck vessels. Aorta is the LVOT with a direction of flow initially from left to right: The anatomical arrangements of the great arteries at their origins with the RVOT crossing over the LVOT is called the cross over. The VOTs are at perpendicular angle to each other and this is a very important characteristic of a normal heart. .
- There are several approaches that the examiner can use to identify the OFTs of the heart that use the 4CV as the initial reference image. One of the techniques is SWEEP TECHNIQUE It was described by Yoo and Yagel. It involves sweeping the transducer beam in a transverse plane from the level of 4CV towards the fetal head. This offers a systematic way of assessing the fetal heart and provides the various views through which normality of the OFT views can be ascertained.
- LVOT is a long axis view of the heart, highlighting the path from the LV into the ascAo. It confirms the presence of the great vessel originating from the morphological LV. We check. LV long axis view: Outflow existence
- In this view RV should be anterior to the LVOT and the LA should be posterior. Continuation of the IVS and anterior wall of aorta should be confirmed. This is called Septaaortic continuity IVS continous with MV when it opens. Valve excursions: Amaç: aorta çıkışını kontrol etmek; öz. Conotruncal anomaliler checking the aorta as it leaves the LV. Helps to identify outlet VSD and conotrunchal abnormalities. Possible to trace the aorta into its arch.
- RVOT is a long axis view of the heart, highlighting the path from the RV into the MPA It confirms the presence of the great vessel originating from the morphological RV. MPA normally arises from the RV and course towards the left of the more posterior ascAo. Thus, MPA should be anterior and to the left of the asc. aorta This confirms the rrossover of AO and PA In this level, often SVC to the right of aorta is seen. The great vessel originating from the morphological RV can only be confirmed as MPA if it branches after a short course. The take-off of the right branch of the PA comes first and the left branch subsequently. But the latter division cannot always be seen owing to the position of the fetus. The normal PA continues distally towards the left side and into the DA that connects to the dAo.
- 3VV and 3VT These additional cross sectional views of the aorta and PA can be obtained by further sliding or tilting the transducer towards the fetal head from the RVOT, so are part of a continous sweep starting from the RVOT. These views show different aspects of the great vessels , define their relationships with each other and with their surrounding structures (SVC and trachea). Clear visualization of this plane indicates that the crossing of the aorta and pulmonary artery is normal
- The3VV depicts the relatively parallel relationship of the SVC, AO, and PA after the latter 2 cross each other . 3VV Yoo et al. described this view to evaluate PA, aA , SVC , and their relative sizes and relationships. Briefly, an assesment of the vessel no, size, alligment and arrangements needs to be made. From left to right, and from anterior to posterior: the relative diameters decrease a and there is a straight alignment staring with PA, then aAo, and finally SVC. TGA, Fallot, Pulmonary atresia with a VSD
- The 3VT view completes the great vessels evaluation: Yoo et al. described this view which is a more cephalad image, in which the transverse aortic arch is better visualized: This is also called the aortic arch view and its relation with the trachea is emphasized.
- Trachea is usu. identified as a hyperechogenic ring surrounding a small fluid filled space. Both arches are positioned to the left of the trachea and form a ‘V’ shape as the both join the descAo. This view is important because it illustrates the transverse aortic arch (TA) and the DA merging with the thoracic aorta. The aaortic arch is the most superior of the two, therefore, to image both arches simultaneously may require some transducer adjustments, away from the plane that is parallel to the 4CV. Coarctation of aorta, right aortic arch, doublr aortic arch, vasular rings are detected.
- SLIGHT: COLOR FLOW DOPPLER Highlights abnormal blood flow patterns May faciliate better visualization of cardiac anatomy in obese May improve detection rate of CHD in low risk group Optimal color Doppler settimgs Narrow color box (region of interest) Since this hast the greatest impact on frame rate Appropriate pulse repetion frequency Low color persistence Adequate gain settings to display flow across vales and through vessels.
- Visceral / abd. situs Cardiac situs Cardiac axis Cardiac size Pericardial effusion FHR and ryhtym Number of cardiac chambers Atrias: Atrial anatomy