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Optimize Screening of the Fetal Heart

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The keys to optimizing screening of the fetal heart are to understand how the ultrasound machine’s functions and controls can affect your image, utilize the entire maternal abdomen, adjust your image presets, and optimize your angle of insonation. So how do you do all that?

You start with the transducer. Be sure to select a transducer that allows for adequate penetration and optimal resolution. All transducers have different operating frequencies and capabilities; high frequencies produce better detail resolution but, of course, with limited sound penetration. These frequencies can be applied in all trimesters, particularly since the advent of high-resolution transducers, which are helpful when imaging delicate heart structures, such as the valves and vessel walls. If, however, the imaging is subpar with a high-frequency transducer, switch to a low-frequency transducer, which is more useful in your patients with a high body mass, in the late second trimester, in the third trimester, and in the event that there is also polyhydramnios syndrome, even when there is rib shadowing. Keep in mind too, that transvaginal imaging is helpful for evaluating the fetal heart in the first or early second trimester, in the event that there is suspected fetal cardiac abnormality, and even when maternal body habitus causes imaging to be difficult.

For your next step, adjust your image presets to optimize your temporal resolution so that you maintain a high frame rate of greater than 25 frames per second. A few of the technical settings that affect temporal resolution are the frame rate (in Hz), frequency selection, depth & focus, sector angle width, and zoom magnification. The better the temporal resolution, the improved detail resolution. To optimize your image, avoid unnecessary depth and make sure your focus is on the region of interest. A multiple focal zone may be applied to structures that don’t move, such as the placenta, but when looking at the 4-chamber heart, you will need a single focal zone. In addition, adjust your sector angle width. Reducing it increases lateral line density, which improves the image quality. Finally, make small adjustments to your settings, such as applying speckle-reduction imaging, adjusting the dynamic range (more or less gray), and scanning in different tones.

When incorporating color Doppler, the color box, color gain, wall motion filter, velocity scale/pulse repetition frequency (PRF), balance, and angle of insolation can each affect the image. The color box slows the frame rate by a significant degree so the smaller the color box, the higher the frame rate. Set color gain initially on low (ie, less color) and gradually increase it until you have optimized the amount of color. The wall motion filter eliminates signals caused by wall motion and low velocities. The velocity scale is the range of mean velocities or PRF in the region of interest. If it is too low, it can produce aliasing, which could lead to a misdiagnosis; too high and the low-velocity flow will not be displayed. Here is a sample of potential ideal velocity flows:

High-velocity flow (>60–80 cm/sec)Low-velocity flow (<30 cm/sec)
Atrioventricular valvesPulmonary veins
Semilunar valvesBicaval (IVC/SVC)
The great vessels (3VV)Evaluating atrial and ventricular septum
The scale is dependent on factors such as body mass index and fetal positioning within the uterus.

The balance allows you to display how much grayscale and color Doppler information you would like to see. Reducing the balance will show grayscale elements within the color box. And, finally, the angle of insonation is very important to keep in mind as the signal from the transducer should be parallel to the direction of blood flow.

J of Ultrasound Medicine, Volume: 35, Issue: 1, Pages: 183-188, First published: 01 January 2016, DOI: (10.7863/ultra.15.02036)

One of the major challenges in ultrasound imaging is scanning a morbidly obese patient. This is a result of the increased distance between the transducer and fetal anatomy, causing degraded resolution. Some techniques for optimizing your imaging in these cases include scanning above the tissue, when the patient’s bladder is full, through the umbilicus, or when the patient is in the Sim’s position (with the patient on their left side), which allows the extra tissue to fall to the left side. Also, keep in mind that when scanning an obese patient, the color doesn’t always fill in. Lowering the color attenuation can help clarify the image.

So, remember, the key to optimizing your fetal heart imaging is in understanding your machines’ functions and controls and how they can affect your image, utilizing the entire maternal abdomen, adjusting your image presets, and optimizing your angle of insonation!

To learn more and see case scenarios, see the American Institute of Ultrasound in Medicine’s (AIUM’s) on-demand webinar with speaker Mishella Perez, MS, RDMS, RDCS, “Fetal Heart Image Optimization: The Key to Screening”, from which this post was adapted. AIUM members can access the webinar for free.

Interested in learning more about fetal imaging? Check out the following resources from the American Institute of Ultrasound in Medicine (AIUM):

See a Need; Fill a Need

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The Increasing Demand for the Detailed Fetal Echocardiogram & Specialization of the Fetal Cardiac Sonographer

With congenital heart defects (CHDs) continuing to lead the pack of anomalies resulting in infant mortality (1) the need for detailed cardiac screening of the developing fetal heart remains a pertinent and valuable tool for obstetrical providers and their patients.

Fetal echocardiography was derived for the purpose of improving antenatal detection rates of fetal cardiac defects. Identification of these in utero can initiate referrals to perinatology, genetic counseling, and pediatric cardiologists where parents can gain further insight about the suspected anomaly, as well as consult about any recommendations and/or expected outcomes. Timely diagnosis can provide the opportunity for a planned delivery at a tertiary center that is properly equipped to provide any necessary support and/or intervention the afflicted newborn may require.

While the basic evaluation of the heart remains part of the fetal anatomical survey (2), obtaining even the standard cardiac views continues to be a challenge in many cases, as adequate views are dependent on many factors including fetal position, maternal body habitus, and sonographer experience.

In order to provide you a visual of why imaging a fetal heart can pose such a challenge for sonographers, keep in mind that the fetal heart is roughly the size of a quarter (3) at 20 weeks of gestational age, which happens to be the timeframe of when most detailed anatomical surveys are attempted. Even more impressive is the fact that the pulmonary veins, whose anomalous drainage can be fatal if undetected prior to delivery, are comparable in size to Jefferson’s nose on the nickel. It has been my experience, if you ask any sonographer performing obstetrical exams which organ is the most difficult to assess on the anatomical survey, the fetal heart likely sits somewhere near the top of their list.

However, the demand for fetal echocardiography is expanding as the understanding of congenital heart disease continues to identify specific populations that have an increased risk of having a fetus with a CHD. (4) This lengthy list of indications for the fetal echocardiogram has historically been divided up into 2 main categories: maternal risk factors and fetal risk factors. As the number of indications for the exam continues to grow larger, so does the need to have highly trained and competent OB sonographers who go on to become certified in fetal echocardiography.

I must also point out that it is a necessity for all sonographers performing anatomical surveys to sharpen their skills at obtaining fetal cardiac images as even with the established indications, congenital heart defects continue to be the most missed anomaly on the prenatal screening sonogram. (5) This is a great example of why continuing education in the sub-specialty of fetal echo, as well as standardized protocols and training, is so important for all of us. Increasing prenatal detection rates of CHDs is a community effort that we can all contribute towards.

The challenge of deepening one’s understanding of fetal cardiac anatomy/physiology, and becoming more proficient at obtaining the detailed fetal echo views, remains an intimidating next-step for many OB sonographers. However, I personally invite those sonographers to face this challenge head-on, understanding that with experience and time, you’ll feel more confident and capable of completing a detailed fetal heart study with every fetal echo you perform.

Fetal echocardiography is a prime example of how something can be both extremely challenging and yet incredibly fulfilling at the same time. Detection of even the smallest cardiac defect in utero can later prove to have made a significant impact on the neonatal management of the newborn and positively impact infant mortality rates in the cases of more severe cardiac lesions. You may ultimately become a key factor in ensuring that your patients get the postnatal care that they require and deserve.

References

(1) Maulik D, Nanda N, Vilchez G. A brief history of fetal echocardiography and its impact on the management of congenital heart disease. Echocardiography 2017; 34:1760–1767.

(2) Pellerito J, Bromley BS, et al. AIUM-ACR-ACOG-SMFM-SRU Practice parameters for the performance of standard diagnostic obstetric ultrasound examinations. J Ultrasound Med 2018; 9999:1–12.

(3) Drose JA. Scanning: indications and technique. Fetal Echocardiography. Philadelphia, PA: Saunders; 1998:15–16.

(4) Wesley L, Anton T, et al. AIUM Practice parameter for the performance of fetal echocardiography. J Ultrasound Med 2020; 39:E5–E16.

(5) Abuhamad A, Chaoui R. Guidelines for the sonographic screening and Echocardiogram of the fetal heart. A Practical Guide to Echocardiography: Normal and Abnormal Hearts. 3rd ed. Wolters Kluwer; 2015:13.


Jaime Taylor-Fujikawa, BS, RDMS, RDCS, is a perinatal sonographer/fetal echocardiographer at The Center for Genetics and Maternal Fetal Medicine in Springfield, Oregon. She is a graduate of The Seattle University Diagnostic Ultrasound Program, class of 2005. She is a wife and mother to two boys.


Interested in learning more about Obstetric Ultrasound? Check out the following posts from the Scan: