Potential pitfalls and methods of improving in utero diagnosis of transposition of the great arteries, including the baby bird's beak image

Pathogenesis and Surgical Treatment of Dextro-Transposition of the Great Arteries (D-TGA): Part II

Dextro-transposition of the great arteries (D-TGA) is the second most common cyanotic heart disease, accounting for 5-7% of all congenital heart defects (CHDs). It is characterized by ventriculoarterial (VA) connection discordance, atrioventricular (AV) concordance, and a parallel relationship with D-TGA. As a result, the pulmonary and systemic circulations are separated [the morphological right ventricle (RV) is connected to the aorta and the morphological left ventricle (LV) is connected to the pulmonary artery]. This anomaly is included in the group of developmental disorders of embryonic heart conotruncal irregularities, and their pathogenesis is multifactorial. The anomaly's development is influenced by genetic, epigenetic, and environmental factors. It can occur either as an isolated anomaly, or in association with other cardiac defects. The typical concomitant cardiac anomalies that may occur in patients with D-TGA include ventriculoseptal defects, patent ductus arteriosus, left ventricular outflow tract obstruction (LVOTO), mitral and tricuspid valve abnormalities, and coronary artery variations. Correction of the defect during infancy is the preferred treatment for D-TGA. Balloon atrial septostomy (BAS) is necessary prior to the operation. The recommended surgical correction methods include arterial switch operation (ASO) and atrial switch operation (AtrSR), as well as the Rastelli and Nikaidoh procedures. The most common postoperative complications include coronary artery stenosis, neoaortic root dilation, neoaortic insufficiency and neopulmonic stenosis, right ventricular (RV) outflow tract obstruction (RVOTO), left ventricular (LV) dysfunction, arrhythmias, and heart failure. Early diagnosis and treatment of D-TGA is paramount to the prognosis of the patient. Improved surgical techniques have made it possible for patients with D-TGA to survive into adulthood.

Prenatal diagnosis of transposition of the great arteries: an updated review

Simple transposition of the great arteries (TGA) is a cyanotic heart disease that accounts for 5% to 7% of all congenital heart diseases. It is commonly underdiagnosed in utero, with prenatal detection rates of less than 50%. Simple TGA is characterized by ventriculoarterial discordance, atrioventricular concordance, and a parallel relationship of TGA. The prenatal diagnosis of TGA influences postnatal outcomes and therefore requires planned delivery and perinatal management. For these reasons, it is important to identify the key ultrasound markers of TGA to improve the prenatal diagnosis and consequently provide perinatal assistance. The presence of two vessels instead of three in the three-vessel tracheal view, a parallel course of TGA, and identification of the origin of each of TGA are the key markers for diagnosing TGA. In addition to the classical ultrasound signs, other two-dimensional ultrasound markers such as an abnormal right convexity of the aorta, an I-shaped aorta, and the "boomerang sign" may also be used to diagnose TGA in the prenatal period. When accessible, an automatic approach using four-dimensional technologies such as spatio-temporal image correlation and sonographically-based volume computer-aided analysis may improve the prenatal diagnosis of TGA. This study aimed to review the ultrasound markers that can be used in the antenatal diagnosis of TGA, with a focus on the tools used by ultrasonographers, the obstetric and fetal medicine team, and perinatal cardiologists to improve the diagnosis of this condition.

The Extended Fetal Cardiac Examination: Is It Feasible in a High-Risk Practice?

The aims of this study were to demonstrate the feasibility of obtaining additional cardiac views as proposed on an extended fetal cardiac examination and to see if there was any variation in individual components of that examination stratified by sonographer training, patient body habitus, or equipment. We retrospectively reviewed 200 consecutive detailed second-trimester high-risk fetal obstetric sonograms that included additional extended cardiac views. We analyzed the percentage of the time individual views were obtained, with variation based on (1) a sonographer with greater than 3 years of training compared with a group with 6 to 12 months of training, (2) 2 different ultrasound units, and (3) different body mass indices. Overall, the highest rate of visualization was achieved with the 4-chamber view (98.2%), whereas the 3-vessel tracheal view had the lowest percentage of visualization (40.2%), among the less experienced sonographers. Differences in successful completion of the extended cardiac views were not statistically different between the sonographer with a level of training greater than 3 years as compared with those with 6 to 12 months' training except for the 3-vessel tracheal view (P < 0.001). There is no statistically significant difference in our ultrasound equipment, when considering only inexperienced sonographers. Increasing body mass index had an inverse relationship with obtaining the components of the detailed cardiac examination. Using state-of-the-art ultrasound equipment and with focused additional training of obstetric sonographers, the majority of extended cardiac views can be obtained. There are exceptions.

Assessment of the Fetal Heart During Routine Obstetrical Screening, a Standardized Method

Assessment of the fetal heart during routine obstetrical screening remains a challenge for sonographers and physicians. Reliance on still images and nonstandard methods of acquiring images and assessing the fetal heart contribute to the relatively low rate of identification of congenital heart disease (CHD). A standardized assessment of the fetal heart using two cine-loop sweeps has been shown to address some of these challenges. Image acquisition using two cine-loop sweeps combined with a standardized five-step assessment is proposed to address the limitations of the nonstandard approach in place at most screening centers today.

Screening for Congenital Heart Disease

Compared with the assessment of most fetal anatomic structures, the assessment of the fetal heart during routine obstetric screening represents a diagnostic challenge for sonographers and interpreting physicians. This is due to a number of factors: the structural complexity of the heart, the rate at which it moves, the position of the fetus relative to the transducer, and variations in assessment protocols used by sonographers and physicians. The fetal heart is a relatively small and complex structure, as seen in an early second-trimester sonogram. In some forms of congenital heart disease, the abnormality may be detectable within only a relatively small fraction of the heart volume. Congenital heart disease represents a range of structural defects, a number of which have specific sonographic features that can be identified during routine assessment. Many approaches have been proposed to improve the assessment of the fetal heart, including specific still images, color Doppler, 3D imaging techniques, and cineloops.

Is the "I-Sign" in the 3-Vessel and Trachea View a Valid Tool for Prenatal Diagnosis of D-Transposition of the Great Arteries?

Prenatal diagnosis of D-transposition of the great arteries remains less frequent compared to other major congenital heart defects. In this study, we examined how often the 3-vessel and trachea view was abnormal in a large series of prenatally diagnosed cases of D-transposition of the great arteries. We found that an abnormal 3-vessel and trachea view in the shape of an "I" ("I-sign"), which represents an anteriorly displaced aorta, was present in all fetuses with D-transposition of the great arteries when a 3-vessel and trachea view was successfully obtained. Therefore we believe that the 3-vessel and trachea view can be used to reliably detect D-transposition of the great arteries during prenatal sonography.

Increasing the detection rate of congenital heart disease during routine obstetric screening using cine loop sweeps

OBJECTIVES

The purpose of this study was to demonstrate an increase in the detection rate of fetal cardiac defects using 2 cine loop sweeps.

METHODS

Image reviewers examined a series of 93 cases randomly sorted, including 79 studies with normal findings and 14 studies with abnormal findings. All of the images were assessed by 5 standard criteria. Cases were classified as normal, abnormal, or indeterminate. Reviewers using the conventional approach reviewed 3 still images: the 4-chamber, left ventricular outflow tract, and right ventricular outflow tract views. Reviewers using the cine loop sweeps viewed 2 grayscale sweeps through the fetal heart in real time. The image sequences were reviewed independently by 2 experts, 3 nonexperts, and 2 sonographers blinded to each others' results.

RESULTS

The cine loop sweeps had an increased detection rate of 38% for the nonexperts and 36% for the experts compared with the conventional approach. The cine loop sweeps allowed identification of all cardiac defects by at least 2 of the 7 reviewers; the percentage of cases with false-positive findings was 3.9%. With the conventional approach, 2 defects went undetected by all reviewers, and 4 defects were found by only 1 reviewer; the percentage of cases with false-positive findings was 5.4%.

CONCLUSIONS

The use of cine loop sweeps has the potential to increase the detection of fetal cardiac defects without increasing the rate of false-positive findings or increasing the interpretation and decision-making times.

Rightward convexity of the great vessel arising from the anterior ventricle: a novel fetal marker for transposition of the great arteries

OBJECTIVES

Traditionally transposition of the great arteries (TGA) is suggested by bifurcation of the great vessel arising from the posterior ventricle and the parallel course of the great vessels as they leave the heart. These findings may be difficult to demonstrate, requiring additional fetal echocardiographic features to indicate TGA. In this study, we investigated a new marker of TGA, namely rightward convexity of the great vessel arising from the anterior ventricle.

METHODS

We reviewed fetal studies from 2006 to 2010 in which an antenatal diagnosis of TGA was confirmed postnatally. We specifically viewed images obtained by scanning the great vessel arising from the anterior ventricle cranially to the superior mediastinum at the level of the three vessels and trachea view and compared them with similar views in normal hearts.

RESULTS

In 21 cases of confirmed TGA, the great vessel arising from the anterior ventricle (aorta) coursing cranially demonstrated an abnormal convexity to the right. This was in contrast to convexity to the left or lack of convexity of the great vessel (pulmonary artery) arising from the anterior ventricle in fetuses with a normal heart. In two fetuses rightward vessel convexity from the anterior ventricle was the clue on the initial scan suggesting TGA, which was subsequently confirmed. In addition, only two vessels, the superior vena cava and aorta, were demonstrated in fetuses with TGA, the pulmonary artery and ductus arteriosus lying below (caudal to) the transverse arch.

CONCLUSIONS

Noting the rightward convexity of the great vessel arising from the anterior ventricle may aid in the prenatal diagnosis of TGA. Furthermore, the relative simplicity of this sign may make it valuable in fetal screening for this cardiac defect.

Fetal diagnosis of interrupted aortic arch

To determine the frequency of prenatal detection among liveborn patients with an interrupted aortic arch (IAA), the accuracy of prenatal diagnosis, and the anatomic features associated with IAA in the fetus. The prenatal diagnosis of an IAA is challenging. The data on the features and outcomes of fetal IAA are limited. This was a retrospective review of the fetuses and neonates diagnosed with IAA at the Children's Hospital Boston. From 1988 to 2009, 26 fetuses were diagnosed with an IAA. Of these, 21 were live born, and 5 pregnancies were terminated. Of these 21 patients, 18 were confirmed to have an IAA after birth and 3 had severe aortic coarctation. Of the 56 patients diagnosed with an IAA as neonates, 3 had a prenatal echocardiogram that did not include the correct diagnosis. Among the liveborn patients with a postnatally confirmed IAA, 24% were diagnosed prenatally, which increased from 11% during the first 7-year period to 43% more recently. Also, 15% of the prenatally diagnosed patients with IAA had a family history of structural or genetic anomalies. In fetuses with an IAA, echocardiographic Z-scores for the aortic valve and ascending aorta were significantly lower than in normal fetuses, but the left ventricular dimensions were normal. Aortopulmonary diameter ratios were abnormally low. In conclusion, although the identification of IAA on a prenatal echocardiogram can be challenging, a number of anatomic features can facilitate the diagnosis. In particular, a low aortopulmonary diameter ratio in the absence of a ventricular size discrepancy should prompt consideration of this diagnosis. Despite the diagnostic challenges, the frequency of prenatal diagnosis of the IAA is increasing.

A primer for fetal cardiac imaging: a stepwise approach for 2-dimensional imaging

Detection of congenital heart disease (CHD) remains problematic, even with advances in imaging. Imaging modalities, such as magnetic resonance imaging, have been helpful in better understanding certain abnormalities, such as the fetal central nervous system. However, because of cardiac motion, screening and detection of CHD are best performed by sonography. Although newer technical advances in sonography, including 3-dimensional (3-D) dynamic multiplanar imaging and Doppler techniques, are extremely helpful in better delineating CHD, the mainstay of detection of CHD remains 2-D real-time imaging. Understanding 2-D imaging of the heart, using multiple views, is necessary to perform any type of multiplanar imaging as both require basic understanding of the same basic views. Although it is beyond the scope of this article to review all facets of fetal cardiac imaging, we will present a stepwise approach using 2-D imaging in the detection of CHD.