Cor triatriatum or divided atriums: which approach provides the better understanding?

It is frequent, in the current era, to encounter congenital cardiac malformations described in terms of "cor triatriatum". But can hearts be truly found with three atrial chambers? The morphological method, emphasised by Van Praagh et al, states that structures within the heart should be defined on the basis of their most constant components. In the atrial chambers, it is the appendages that are the most constant components, and to the best of our knowledge, hearts can only possess two appendages, which can be of either right or left morphology. The hearts described on the basis of "cor triatriatum", nonetheless, can also be analysed on the basis of division of either the morphologically right or the morphologically left atriums. In this review, we provide a description of cardiac embryology, showing how each of the atrial chambers possesses part of the embryological body, along with an appendage, a vestibule, a venous component, and a septum that separates them. We then show how it is, indeed, the case that the hearts described in terms of "cor triatriatum" can be readily understood on the basis of division of these atrial components. In the right atrium, it is the venous valves that divide the chamber. In the left atrium, it is harder to provide an explanation for the shelf that produces atrial division. We also contrast the classic examples of the divided atrial chambers with the vestibular shelf that produces supravalvar stenosis in the morphologically left atrium, showing that this form of obstruction needs to be distinguished from the fibrous shelves producing intravalvar obstruction.

[Cor triatriatum dextrum resulting from the persistence of embryonic remnants of the right valve of the sinus venosus: prevalence and echocardiographic aspects in a large consecutive non-selected patient population]. / Pseudocuore triatriato destro da persistenza di residui embrionari della primitiva valvola del seno venoso: prevalenza ed aspetti ecocardiografici in un'ampia popolazione consecutiva non selezionata.

BACKGROUND: Cor triatriatum destrum is a rare congenital malformation, usually associated with complex right heart abnormalities, characterized by a membrane that divides the right atrium into two chambers. It is considered the result of the incomplete and abnormal regression of the embryonic right valve of the sinus venosus. When the valve regresses the cephalic portion forms the crista terminalis and the caudal portion develops into the Eustachian and Thebesian valve. With an incomplete regression, a fenestrated or an unfenestrated membrane may persist in the right atrium. We describe the clinical and echocardiographic characteristics of this type of remnants in the right atrium. METHODS: In a 4-month period, 1728 transthoracic two-dimensional and Doppler echocardiographic studies were consecutively performed. RESULTS: Twenty-seven patients (16 males, 11 females, mean age 55 +/- 21 years, range 1-87 years) were occasionally recognized to be affected by a membrane inside the right atrial cavity. On the basis of its echocardiographic appearance (a membranous structure connecting the orifice of the inferior vena cava to the atrial septum with evident fenestration in 74% of cases), absence of associated congenital abnormalities (92.5% of cases), interatrial shunt or abnormal flow pattern of venous systemic return, a diagnosis of a normal benign anatomic variant of sinus venous remnants (similar to the so-called "Chiari's network") could be made in every case. CONCLUSIONS: The incomplete regression of the embryonic right valve of the sinus venosus may leave a fenestrated or an unfenestrated membrane in the right atrium that should be considered a normal benign variant of the so-called "Chiari's network".

[Cor triatriatum sinistrum and atrial septal defect]. / Cor triatriatum sinistrum und Vorhofseptumdefekt.

The cor triatriatum sinistrum is a rare congenital malformation. Frequently, the patients become symptomatic in infancy with clinical signs of severe congestive heart failure. We report on an adult patient with only mild symptoms with cor triatriatum sinistrum and atrial septal defect. The embryological basis of the disorder and the hemodynamic conditions which permitted this patient to remain symptom free for a long period are discussed.

[The pathological remnants of the right sinus venosus valve. A presentation of 6 hearts of the cor tritriatum dexter type]. / Derivados patológicos de la valva derecha del seno venoso. Presentación de seis corazones de tipo cor triatriatum dextrum.

Six hearts specimens of cor triatriatum dextrum, eight with the Chiari's network, and 3 with a membranous remnant of the crista terminalis are studied. These anomalies are interpreted as varying degrees of persistence of the right valve of the sinus venous which reflect different stages of their morphogenesis. The most frequent congenital heart defects associated with these sinus remnants are the absence of a right atrioventricular connexion and pulmonary atresia with intact ventricular septum. There may be some haemodynamic factors in the right atrium such as partial of complete obstruction between the atrium and the right ventricle which explain the fact that the valve is not reabsorbed. In our specimens the persistent right valve divided the right atrium into two compartments; one is located in the medial sinusal portion where both cavae veins and coronary sinus are connected; the other is lateral compartment which represents the primitive right atrium. It must be noted that the persistent right valve favors blood flow to the left atrium through the patent foramen ovale or through an atrial septal defect deviating the course of the blood away from the right ventricle. This could cause the hypoplasia of the right ventricle. When the valve bulges it obstructs the blood flowing into the right ventricle. The diagnosis of these malformations can be made by echocardiographic, angiocardiographic procedures and nuclear magnetic resonance.

Cor triatriatum dexter: two-dimensional echocardiographic diagnosis.

Cor triatriatum dexter is a malformation resulting from lack of normal regression of the embryonic right valve of the sinus venosus. In this situation, the right atrium is divided by a membrane into two chambers. Two-dimensional echocardiography was used in the antemortem diagnosis of this rare cardiac anomaly in a neonate. Associated cardiac lesions were also documented. The patient died, and findings were verified at autopsy.