Cor Triatriatum Dexter

Cor triatriatum dexter is a rare cardiac anomaly characterised by division of the right atrium into two compartments. This division is usually caused by a fenestrated membrane, which represents the persistence of the remnants of the right valve of the embryonic sinus venosus^1-3. Cor triatriatum dexter represents the most severe form of the failure of regression of the right sinus venosus valve. The presence of this membrane may favour the passage of blood flow from the inferior vena cava to the interatrial septum and obstruction of blood flow to the right ventricle.

The mere presence of this membrane does not condition a Cor triatriatum dexter; the term should be restricted to only those cases where the presence of this membrane interferes with the passage of blood through the right atrium^1,4.

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Cor triatriatum dexter is a very rare congenital heart defect. It is estimated to account for 0.1-0.4% of all congenital heart defects³.

During the embryonic period the sinus venosus is surrounded by a left and a right valve. Between 9 and 15 weeks of gestation, the left valve becomes incorporated into the septum secundum and the right valve involutes. The cephalic portion of the right valve becomes the crista terminalis and the caudal portion divides into the Eustachian valve (inferior vena cava valve) and the Thebesian valve (coronary sinus valve)^2-5,7.

When there is an interruption or defect in the regression of the right sinus venosus valve, a membrane persists causing a separation of the right atrium into two compartments. The degree of severity of this anomaly results in a wide spectrum of right atrial and tricuspid valve obstruction:

• In mild forms there is a prominent Eustachian and/or Thebesian valve.
• Moderate forms are characterised by a prominent fenestrated membrane/network, referred to as Chiari net. It is estimated that approximately 2% of the population may have a prominent Chiari network.
• Cor triatriatum dexter represents the most severe form of anomalous regression of the right valve of the sinus venosus. There is a fenestrated membrane that divides the right atrium into two compartments and causes obstruction to the passage of blood into the right atrium and tricuspid valve^4,5,7.

The cause of the defect in the regression of the right sinus venosus valve is unknown.

In Cor triatriatum dexter the presence of the membrane in the right atrium causes blood flow from the inferior vena cava to be directed into the interatrial septum through the foramen ovale and consequently decreases blood flow through the tricuspid valve into the right ventricle. Sometimes this membrane also interferes with the passage of blood through the tricuspid valve by prolapsing through it.

The clinical manifestations will be conditioned by the degree of septation, which determines the degree of obstruction to the passage of blood to the right ventricle.

• In mild cases, the result of failure of venous sinus valve is usually asymptomatic, and many cases are postmortem autopsy findings.
• When the obstruction is moderate, symptoms of right heart failure and increased central venous pressure may occur, due to obstruction of blood flow through the inferior vena cava, tricuspid valve and right ventricle.  It may also present clinically as a patent foramen ovale and with the presence of paroxysmal embolisms. Cyanosis is frequent in children with Cor triatriatum dexter.
• In the most severe cases this compartmentalisation of the right atrium will lead to the presence of right ventricular hypoplasia to varying degrees, this being the most frequently associated congenital cardiac anomaly^2,5,8,9.

Cor triatriatum dexter is often found in association with other cardiac anomalies such as atrial septal defects, venous return anomalies such as persistent left superior vena cava, Ebstein's anomaly, pulmonary hypoplasia or atresia and especially hypoplastic right ventricle^2,4,9.

Cases associated with increased nuchal translucency in the first trimester have been reported⁴.

No extracardiac abnormalities or genetic or chromosomal syndromes associated with Cor triatriatum dexter have been documented⁷.

The diagnosis of Cor triatriatum dexter can be made by 2D ultrasound in the four-chamber view. An abnormal four-chamber view shows a fluctuating membrane in the right atrium, which divides the right atrium into two compartments. This membrane protrudes into the tricuspid valve during cardiac diastole^2,9. 

Prenatal diagnosis of Cor triatriatum dexter can be difficult. There are few cases published in the literature where the diagnosis has been made at the fetal stage^2.4. In many cases the diagnosis is made prenatally when there is another associated cardiac anomaly, the most frequent being right ventricular hypoplasia (a consequence of the obstruction of ventricular filling due to the presence of the membrane).

In most cases the diagnosis is made by transthoracic or transesophageal echocardiography in childhood or adolescence, and also during a necropsy study^3-5,7,9,14. It is often an echocardiographic finding in paediatric patients with cyanosis.

The variability in clinical presentation causes a real diagnostic challenge, ranging from asymptomatic cases to those with significant associated abnormalities.

The differential diagnosis of Cor triatriatum dexter must be made with those pathologies that present a membrane or membrane-like structure in the right atrium. There are cardiac tumours that could be confused with this pathology. The presence of a Chiari network is, in a large number of cases, the diagnosis most often confused with this entity, being a milder form of the same embryological alteration. Other milder forms such as the presence of a prominent Eustachian or Thebesian valve may also have a similar presentation.

Protrusion of the membrane across the tricuspid valve can mimic Ebstein's anomaly and can sometimes be confused with this anomaly^2,7,9,12-13. 

Cor triatriatum dexter should be a pathology included in the differential diagnosis of hypoplastic right ventricle⁷, along with other cardiac anomalies such as tricuspid atresia, tricuspid dysplasia, pulmonary atresia with intact septum and Ebstein's anomaly.

The main diagnostic clue for Cor triatriatum dexter is the presence of discordance of the cardiac chambers, with predominance of the left cardiac chambers. In the context of right ventricular hypoplasia, the presence of a membrane in the right atrium that may cause obstruction to blood flow through the tricuspid valve should be assessed.

The size of the right ventricle, which is the main prognostic factor in this pathology, must be adequately assessed. Likewise, the size of the pulmonary artery must be assessed.

The prognosis will depend on the degree of obstruction.

In cases where the membrane does not cause significant obstruction to blood flow, the prognosis is good.  When the membrane causes severe obstruction to blood flow leading to right ventricular hypoplasia, and occasionally pulmonary hypoplasia due to low flow, the prognosis worsens. The major prognostic factor is the size of the right ventricle.

Prenatal management will depend on the degree of severity of this pathology, with the size of the right ventricle being the main prognostic factor.

Prenatal counselling in the presence of Cor triatriatum dexter may be difficult due to the uncertainty that may exist in early stages about the future neonatal circulation, which may be biventricular (better prognosis) or univentricular (worse prognosis).

In continuing pregnancies, the presence of this pathology does not modify the usual obstetric management. There is no indication for elective caesarean section in the presence of Cor triatriatum dexter. In the presence of right ventricular hypoplasia or pulmonary artery hypoplasia, delivery in a tertiary centre is recommended.

1. Hansing CE, Young WP, Rowe GG. Cor triatriatum dexter. Persistent right sinus venosus valve. Am J Cardiol. 1972 Oct;30(5):559-64. doi: 10.1016/0002-9149(72)90050-1.
2. McLean G, Menahem S, Teoh M. Prenatal diagnosis of cor triatriatum dexter. Ultrasound Obstet Gynecol. 2010;36(6):777-778. doi:10.1002/uog.8837
3. Vigna R, De Paola N, Cignini P, Padula F. An isolated fetal cor triatriatum dexter during a targeted anatomic survey at 22 weeks' gestation. J Prenat Med. 2008;2(4):47-48.
4. Maroun LL, Graem N, Skibsted L. Fetal cor triatriatum dexter: a report of two cases associated with nuchal edema in early second trimester. Pediatr Dev Pathol. 2008;11(1):59-62. doi:10.2350/07-04-0261.1
5. Mazzucco A, Bortolotti U, Gallucci V, Del Torso S, Pellegrino P. Successful repair of symptomatic cor triatriatum dexter in infancy. J Thorac Cardiovasc Surg. 1983;85(1):140-143.
6. Church WS. Congenital malformation of the heart; abnormal septum in the left oricle. Trans Pathol Logic Soc 1868; 19:415-22.
7. Lasa JJ, Westover T, Khandelwal M, Cohen MS. Cor triatriatum dexter and right ventricular hypoplasia in a fetus. J Ultrasound Med. 2011;30(12):1744-1747. doi:10.7863/jum.2011.30.12.1744
8. Imachi T, Arimitsu K, Minami M, Hayakawa M, Kawaguchi A. Cor triatriatum dexter with anomalous pulmonary venous drainage and sinus venosus atrial septal defect. J Thorac Cardiovasc Surg. 1988;95(4):734-737.
9. Fesslova V, Saracino A, Nuri H, Pomé G. Cor triatriatum dexter: unusual features in utero and after birth. Interact Cardiovasc Thorac Surg. 2012;14(3):330-332. doi:10.1093/icvts/ivr096
10. Doucette J, Knoblich R. Persistent right valve of the sinus venosus. So-called cor triatriatum dextrum: review of the literature and report of a case. Arch Pathol 1963; 75: 105-112.
11. Caliskan M, Erdogan D, Gullu H, Muderrisoglu H. Cor triatriatum dexter in two adult patients. Int J Cardiovasc Imaging. 2006;22(3-4):383-387. doi:10.1007/s10554-005-9021-3
12. Barrea C, Rubay J, Wagner K, Ovaert C. Images in cardiovascular medicine: Cor triatriatum dexter mimicking Ebstein disease. Circulation. 2009;120(11):e86-e88. doi:10.1161/CIRCULATIONAHA.109.859744
13. Salam S, Gallacher D, Uzun O. Cor triatriatum dexter masquerading as Ebstein's anomaly. Cardiol Young. 2011;21(3):354-356. doi:10.1017/S1047951111000023
14. Gussenhoven WJ, Essed CE, Bos E. Persistent right sinus venosus valve. Br Heart J. 1982;47(2):183-185. doi:10.1136/hrt.47.2.183

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