Arq Bras Cardiol: Imagem cardiovasc. 2021; 34(3): eabc204

Cor triatriatum sinister and giant eustachian valve mimicking a tetratrial heart

DOI: 10.47593/2675-312X/20213403eabc204

Introduction

Cor triatriatum is a rare congenital cardiac anomaly that is usually associated with other congenital heart defects such as anomalous pulmonary vein return, atrial septal defect, or patent foramen ovale. Cor triatriatum sinister is found in an approximately 0.1% of necropsy examinations. In this congenital malformation, the left atrium is divided into two chambers, usually by a fibromuscular septum, with the pulmonary veins entering a posterosuperior chamber separated from the anteroinferior distal chamber containing the mitral valve and the left atrial appendage. Although several theories have been hypothesized, its embryologic origin remains not fully understood. An inadequate incorporation of the common pulmonary vein into the left atrium or abnormal growth of the septum primum have been postulated to explain it. On the other hand, cor triatriatum dexter is an even more rare congenital cardiac anomaly in which a membranous structure divides the right atrium into two chambers. In such cases, complete persistence of the right valve of the sinus venosus is responsible for the atrial division. This valve usually regresses as a part of normal embryological development between 9 and 15 weeks’ gestation, leaving behind remnants such as the crista terminalis superiorly and the eustachian valve of the inferior vena cava and the thebesian valve of the coronary sinus inferiorly. The severity of this defect is directly related to the degree of flow obstruction, which in turn is related to the degree of valve persistence.^– Although it shares the same embryologic origin and might show a similar echocardiographic appearance, the differential diagnosis includes a prominent eustachian valve, which also results in an apparent division of the right atrium into two chambers.

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