Department of Cardio-Thoracic Surgery, Nizam's Institute of Medical Sciences, Hyderabad, Andhra Pradesh, India.

Cor-triatriatum is a rare congenital cardiac abnormality in which left atrium (sinister) or the right atrium (dextrum) is divided into two compartments by a fold of tissue or a fibromuscular membrane [1-3]. It is seen in around 0.1-0.4% of the patients with congenital cardiac disorders [4]. It was first described in 1868 by Church [5]. Later in 1905, Borst gave the name cor-triatriatum [6]. In children, it may be associated with other major congenital cardiac anomalies such as tetralogy of Fallot, double outlet right ventricle, coarctation of the aorta, partial anomalous pulmonary venous connection, persistent left superior vena cava to coronary sinus, ventricular septal defect, atrioventricular septal defect, and common atrioventricular canal [7]. Left superior vena cava is more frequently associated when compared to other anomalies [8]. In classical cor-triatriatum, proximal chamber of the left atrium receives pulmonary venous drainage and the distal chamber contains the left atrial appendage will lead to mitral valve [9]. The membrane in between the two chambers will have one or more apertures which can range from small and restrictive to large and wide open. Clinical manifestations depend upon the gradient across this membrane. Cor-triatriatum dextrum is extremely rare and is due to the persistent right sinus valve of the embryonic heart.

A 11-year-old male presented with the complaints of exertional dyspnea NYHA class II intermittently over the last 2 months. Diagnosed with ventricular septal defect since birth, clinical examination revealed a pansystolic murmur. The electrocardiogram (ECG) was unremarkable, while the chest x-ray indicated pulmonary congestion with a dilated pulmonary artery (PA). 

In this case, presence of a persistent left superior vena cava (LSVC) with a dilated coronary sinus closely resembled the echocardiographic features of cor-triatriatum. Persistent LSVC, a relatively common anomaly in systemic venous circulation, occurs in approximately 4% of congenital heart disease cases [10-12]. Typically, both right and left superior vena cavae co-exist, draining into the right atrium through a dilated coronary sinus [13,14]. However, in rare instances, the persistent LSVC may directly drain into the left atrium, causing coronary sinus dilation. This dilation, when adherent to the posterior left atrial wall, can lead to left ventricular inlet obstruction and altered flow across the mitral valve, potentially resulting in elevated pulmonary vein pressure and subsequent pulmonary artery hypertension [15]. While many patients with this anomaly remain asymptomatic and are incidentally discovered during surgical, imaging, or invasive procedures, there is a notable incidence of cardiac arrhythmias and conduction defects. These are believed to be attributed to the stretching and fibrosis of the atrioventricular node or the bundle of His by the dilated coronary sinus [16]. Additionally, the dilated coronary sinus has been implicated in causing left ventricular outflow tract obstruction and heart failure. 

Echocardiography proves to be a sensitive diagnostic tool, emphasizing its importance in identifying cases where the dilated coronary sinus may closely resemble the echocardiographic appearance of cor-triatriatum. This case emphasizes the significance of considering and managing the complexities associated with persistent LSVC, especially in the context of mimicking other congenital cardiac abnormalities.

Contributors: CLA: manuscript writing, patient management; PSSG: manuscript editing, patient management. CLA will act as a study guarantor. Both authors approved the final version of this manuscript and are responsible for all aspects of this study.

Funding: None; Competing interests: None stated.