Case of the Week # 524

Case of the Week # 524

Javier Cortejoso
 on 02/28/2023
 on Tuesday, February 28th, 2023
The images demonstrate the following: the four-chamber view shows that the anterior ventricle is the morphologic left ventricle connecting to the right atrium through the mitral valve. It is characterized by a typical smooth surface and a more elongated appearance, forming the apex of the heart. The papillary muscles of the right-sided mitral valve attach on the side wall of the ventricle. The atrium positioned on the left side is identified as left by the arrival of pulmonary veins and by the fluttering of the foramen ovale inside. The posterior ventricle, which is the right ventricle, communicates with the left atrium. There is apical insertion of the chordae tendineae of the tricuspid valve to the apical part of the ventricle in the region of the moderator band. The atrioventricular valve on this side (tricuspid) shows a more apical insertion than the mitral. Assessment of the outflow tracts shows the pulmonary artery, with an early bifurcation into pulmonary branches, originates from the anterior morphologic left ventricle, showing continuity with the mitral valve. The aorta arises from the left-sided morphologic right ventricle in a parallel course, with the aorta anterior and to the left of the pulmonary artery.

Transposition of the great arteries (TGA) describes a cardiac pathology in which the aorta arises from the morphological right ventricle and the main pulmonary artery from the morphological left ventricle, known as ventriculoarterial discordance. TGA is most frequently associated with normal atrioventricular concordance (D-ventricular looping with a morphologic right ventricle rightward and anterior, and morphologic left ventricle leftward and posterior), a lesion also referred to as D-TGA or complete TGA. Far less commonly, there may be concomitant atrioventricular and ventriculoarterial discordance (double discordance), in which the ventricles are inverted (or L-looped) and the great arteries again arise from the incorrect ventricle: aorta from the left-sided morphologic right ventricle and main pulmonary artery from the right-sided morphologic left ventricle. This last type is referred to as levo-TGA or L-TGA and is currently called congenitally corrected TGA (cc-TGA). The systemic venous return carrying deoxygenated blood travels to the lungs via the right atrium, left ventricle, and pulmonary artery, while the pulmonary venous return carrying oxygenated blood travels to the body via the left atrium, right ventricle, and aorta. There is “physiologic correction” because the normal pathways of deoxygenated blood to the lungs and oxygenated blood to the body persist in the correct manner.

The Baron Karl von Rokitansky, in his atlas of 1875, was the first to describe the entity we now know as congenitally corrected transposition of the great arteries (cc-TGA). It is also known as “L-transposition” or ventricular inversion, although these terms are less precise. It is an uncommon form of congenital heart defect, with a prevalence of 1 in 30,000 live births, less than 1% of all congenital heart disease. Its etiology is likely multifactorial, with rare association of chromosomal abnormalities. The causative embryologic mechanism of cc-TGA is the abnormal looping of the primitive heart tube and abnormal remodeling of the outflow tract. Instead of looping to the right, the cardiac tube loops to the left causing the morphologic right ventricle to the left side of the morphologic left ventricle. As is true for D-TGA, the primitive outflow tract rotates abnormally leading to the parallel relationship of the great vessels with an anterior and leftward aorta in the majority of cases. A mirror-image arrangement of the atria (atrial situs inversus) is present in approximately 5% of patients with physiologically “corrected” TGA. Importantly, patients with a mirror-image arrangement of the atria have a rightward looping (D-ventricular loop) and not leftward looping of the primitive heart tube. For this reason, it is best not to use the term L-TGA.

CC-TGA is the only conotruncal heart disease in which the findings to suggest the diagnosis are present in the four-chamber view. The most reliable feature is the demonstration of atrioventricular discordance in which the atrium with the systemic venous connections (inferior and superior vena cava) connects with the morphologic left ventricle, and the atrium with the pulmonary venous connections connects with the morphologic right ventricle. The inverted relationship of the atrioventricular valves results in the left atrioventricular valve (the tricuspid valve) being more apically displaced than the right atrioventricular valve (the mitral valve). The presence of the moderator band helps to define the right ventricle, which is visible on the left side of the heart. The atrioventricular valves are often dysplastic (thickened, redundant), especially the tricuspid valve.

From the four-chamber view, a sweep cephalad to the ventricular outflow tract confirms the presence of ventriculoarterial discordance. The first vessel arises from the right heart (left ventricle), connects with the atrioventricular valve (mitral valve) by a fibrous tract and morphologically is the main pulmonary artery, with early bifurcation into right and left branches. Sweeping further cephalad, the aorta arises from the right ventricular outlet or infundibulum which is located anterior and leftward to the pulmonary artery. It gives rise to a normally configured supraaortic branching distant from the semilunar valve. The crossover of both arteries cannot be identified because they run in parallel.

The three-vessel and tracheal view is usually abnormal with only two vessels. The course of the aortic arch to the descending thoracic aorta remains to the left of the midline from anterior to posterior, never crossing the midline as occurs in the normal relationship of this vessel.

According to Sharland et al, three echocardiographic features should alert the sonographer to this condition: (1) reversed differential insertion of the atrioventricular valves, (2) the moderator band located in the left-sided or posterior ventricle, and (3) the abnormal orientation of the great arteries. This last point refers to the loss of the normal crossover of the great arteries, and to the fact that the first vessel seen when the probe is moved cranially from the four-chamber view is the pulmonary artery. This finding may also be seen in ventriculoarterial discordance with atrioventricular concordance; therefore, the first two characteristics have to be confirmed to make a correct diagnosis. Paladini et al add that the presence of mesocardia and the altered insertion of the papillary muscles best displayed in a transverse four-chamber view may facilitate recognition of atrioventricular discordance.

Ninety percent of affected patients have associated cardiac anomalies, which contribute to both clinical presentation and outcomes. The most common, in decreasing order of frequency, are ventricular septal defects (present in over 50% of cases; usually large and perimembranous), pulmonary stenosis/atresia, anomalies of the left-sided tricuspid valve (including dysplasia, Ebstein-like attachment, and tricuspid atresia), as well as rhythm disturbances and dextrocardia.

The abnormal arrangement of cc-TGA causes a malalignment between atrial and ventricular septum and, consequently, an abnormal pathway of the cardiac conduction system. The atrioventricular node and the bundle of His are positioned more anteriorly than normal and are subject to fibrosis, leading to heart block in some patients. In patients born with normal cardiac conduction, the risk of developing heart block over time increases by 2% per year. Tachyarrhythmias may also occur in the presence of dual atrioventricular nodal pathways or accessory muscular atrioventricular connection.

Fetal outcome in cc-TGA is generally uneventful, unless complicated by severe tricuspid valve dysplasia and regurgitation (Ebstein malformation) or atrioventricular block, leading to fetal hydrops and death. Most neonates with cc-TGA are clinically stable at birth, many without signs or symptoms of congenital heart disease. In the absence of other intracardiac pathology, affected patients can be clinically well for many years and may even go unrecognized until later in life. Features of the pathology such as a morphological right ventricle facing the systemic afterload, various degrees of tricuspid valve dysplasia, and an abnormal atrioventricular conduction pathway contribute to the complications experienced over the course of a normal life span.

The differential diagnosis of cc-TGA includes double outlet right ventricle and D-TGA as they all share the absence of “crossover” of the great vessels. Complete TGA (D-TGA) may look similar initially, but the inversion of the normal ventricular anatomy gives a clue to the correct diagnosis.

Suggested readings:

• Abuhamad A and Chaoui R. Complete and congenitally corrected transposition of the great arteries. In: A practical guide to fetal echocardiography. Normal and abnormal hearts, third edition. Wolters Kluvers, Philadelphia, PA, USA, 2016; pg 447-466.
• Alvarez SGV and Hornberger LK. Transposition of the great arteries. In: Yagel S, Silverman NH, Gembruch U, ed. Fetal Cardiology. Embryology, Genetics, Physiology, Echocardiographic Evaluation, Diagnosis, and Perinatal Management of Cardiac Diseases, 3rd edition. CRC Press, Boca Raton, FL, USA, 2019. pg 372-387.
• Bennasar M, Gómez O, Bartrons J. Transposición corregida de grandes vasos. En: Galindo A, Gratacós E y Martínez JM, ed. Cardiología fetal. Marbán, Madrid, España, 2015; pg 367-372.
• Graham TP, Bernard YD, Mellen BG, et al. Long-term outcome in congenitally corrected transposition of the great arteries: a multi-institutional study. J Am Coll Cardiol. 2000 Jul;36(1):255-61.
• Jaeggi ET, Hornberger LK, Smallhorn JF, et al. Prenatal diagnosis of complete atrioventricular block associated with structural heart disease: combined experience of two tertiary care centers and review of the literature. Ultrasound Obstet Gynecol. 2005 Jul;26(1):16-21.
• Kibar A, Hallioglu O, Erdem S, et al. Prenatal Diagnosis and Postnatal Follow-up of congenitally corrected transposition of the great arteries and recurrent supraventricular tachycardia. Images Paediatr Cardiol. 2013 Jan;15(1):7-11.
• McEwing RL, Chaoui R. Congenitally corrected transposition of the great arteries: clues for prenatal diagnosis. Ultrasound Obstet Gynecol. 2004 Jan;23(1):68-72.
• Natarajan S. Corrected Transposition of the Great Arteries. In: Rychik J and Tian Z, ed. Fetal cardiovascular imaging. A disease-based approach. Elsevier Saunders, Philadelphia, PA, USA, 2012; pg 165-173.
• Paladini D, Volpe P, Marasini M, et al. Diagnosis, characterization and outcome of congenitally corrected transposition of the great arteries in the fetus: a multicenter series of 30 cases. Ultrasound Obstet Gynecol. 2006 Mar;27(3):281-5.
• Sharland G, Tingay R, Jones A, et al. Atrioventricular and ventriculoarterial discordance (congenitally corrected transposition of the great arteries): echocardiographic features, associations, and outcome in 34 fetuses. Heart. 2005 Nov;91(11):1453-8.

You can be the first one to reply!

Sign In to Reply

Add bookmark Bookmarked