Cor triatriatum with supramitral ring: “cor tetratriatum”, associated with Raghib syndrome with Eisenmenger syndrome: multimodality imaging approach in this exceedingly rare case report

Background Cor triatriatum and supramitral ring are congenital anomalies which result in formation of three chambers of atria. To the best of our knowledge, simultaneous presence of both entities in the same patient resulting in the formation of four chambers of atria has not been described in the literature. Here, we report a case of simultaneous presence of cor triatriatum and supramitral ring associated with Raghib syndrome and Eisenmenger syndrome. Case presentation We report the case of a middle-aged gentleman, who presented to us with features of atrial septal defect with Eisenmenger syndrome. Multimodality imaging confirmed the simultaneous presence of supramital ring and cor triatriatum resulting in “cor tetratriatum” along with Raghib syndrome. Presence of Eisenmenger syndrome compelled us to offer medical therapy for the patient. Conclusion This is the first case report describing the simultaneous presence of supramitral ring and cor triatriatum resulting in a new entity—“cor tetratriatum”. Supplementary Information The online version contains supplementary material available at 10.1186/s43044-021-00183-4.


Background
Cor triatriatum sinister and supramitral ring are congenital anomalies which result in formation of three chambers of atria by a membrane in the left atrium (LA). The position of the membrane differentiates the two entities. In supramitral ring, the membrane is present below the left atrial appendage (LAA), while it is above the LAA in cor triatriatum [1]. To the best of our knowledge, simultaneous presence of both entities in the same patient resulting in the formation of four chambers of atria has not been described in the literature. Here, we report a case of simultaneous presence of cor triatriatum and supramitral ring associated with Raghib syndrome and Eisenmenger syndrome.

Case presentation
A 45-year-old gentleman of north Indian ethnicity, teacher by occupation, with no significant medical, family, or psychosocial history presented to us with complaints of bluish discoloration of mucous membranes, breathlessness on exertion belonging to New York Heart Association (NYHA) functional class 3, and palpitations belonging to modified European Heart Rhythm Association (EHRA) class 3 for 1 year.
Physical examination revealed central cyanosis and grade three clubbing in all four extremities with oxygen saturation of 82% on room air. Other salient features on physical examination included raised jugular venous pressure with prominent cv waves, grade three parasternal heave, a wide fixed split S2 with loud P2, grade two pansystolic murmur (PSM) at apex, and a grade three PSM at lower left sternal border which increased with inspiration. Twelve lead surface electrocardiogram (ECG) showed right bundle branch block (RBBB) with atrial fibrillation (AF) (Fig. 1A). Chest X-ray showed situs solitus, levocardia, right atrial enlargement, right ventricular (RV) apex, and dilated main and right descending pulmonary arteries with peripheral pruning of pulmonary vessels (Fig.  1B). Two-dimensional transthoracic echocardiography (TTE) revealed dilated right-sided chambers and severe tricuspid regurgitation (TR) with a right ventricular systolic pressure of 100mmHg. TTE also revealed an atrial septal defect (ASD) with maximum Cardiac catheterization confirmed these findings ( Fig.  4 E, F, Video 6). Catheterization also revealed irreversible severe pulmonary arterial hypertension (PAH) with resistance ratio of 1.1 and step down in the oxygen saturation from pulmonary veins to LA. Through this multimodality imaging approach, we concluded with a diagnosis of cor triatriatum with supramitral ring: "Cor tetratriatum" with Raghib syndrome with Eisenmenger syndrome. Patient was kept on medical management with tablet torsemide 10mg once daily, tablet metoprolol succinate 50mg once daily, tablet warfarin 5mg once daily, and tablet sildenafil 20mg thrice daily. Follow-up at 1 month, 3 months, 6months, and 1 year showed no progression of symptoms, with the patient remaining in NYHA class 2 and modified EHRA class 2A. The international normalised ratio was maintained in the therapeutic range, and he had no adverse effects to any medications.

Discussion
Supramitral ring is a type of congenital MS which is supposed to have better prognosis than the other types. It is thought to be derived from failure of the endocardial cushions to divide completely. The ring, which is fibrous, can be complete or partial, maybe annular or supraannular and maybe associated with normal or abnormal mitral valve [1].  Cor triatriatum sinister is a rare anomaly due to incomplete incorporation of the pulmonary vein into the LA [2]. It results in the formation of two chambers of LA, the posterosuperior chamber which receives blood from pulmonary veins and the anteroinferior chamber which contains the LAA and mitral valve orifice. The size of the opening in the membrane classifies cor triatriatum into three types. Type 1 has no opening, where the accessory left atrium drains into the right heart, type 2 has a small opening, and type 3 has a large opening with little or no obstruction. Types 1 and 2 present in childhood due to obstruction in pulmonary venous return with pulmonary hypertension, while most patients with type 3 are asymptomatic in childhood [2,3].
Echocardiography is the first-line choice for the evaluation of pulmonary venous anomalies, but it lacks the ability to 3-dimensionally display the pulmonary veins and their relationships to the left atrium. Computed tomography angiography (CTA) is the modality of choice for the diagnosis of pulmonary venous anomalies. It noninvasively and accurately evaluates the presence, course, and number of anomalous veins; associated cardiovascular defects; and any other lung or vascular anomaly with detailed anatomical assessment. It allows rapid acquisition of data with high spatial resolution and wide anatomic coverage. Thus, it is considered superior to echocardiogram and cardiac catheterization. Magnetic resonance imaging (MRI) is an excellent imaging modality for anomalous pulmonary veins. White blood imaging sequences do not always provide sufficient spatial resolution for the more peripheral pulmonary veins, especially when the anatomy is complex. Contrast MRA and time-resolved MRA allow proper visualization of the pulmonary veins; however, it takes a long time. Phase contrast MRI may have a role in evaluation of flow pattern within pulmonary veins. Digital subtraction angiography is a criterion-standard method for assessment of complex congenital heart disease in infants and children, but it is an invasive procedure with high radiation doses [2].
To the best of our knowledge, simultaneous presence of supramitral ring and cor triatriatum has not been described in the literature. Simultaneous presence of both entities in our patient, resulting in formation of four chambers of atria, justifies the term "cor tetratriatum".
Unroofed coronary sinus is a rare congenital heart defect where the wall of the coronary sinus is partially or completely absent. It is classified according to the Kirklin and Barratt-Boyes classification into four types depending on whether the unroofing is complete or partial, and whether associated with PLSVC or not. The type I defect, completely unroofed CS with PLSVC, is called Raghib syndrome. Though this defect can be made out with TTE/TEE, a better imaging modality is bubble contrast TTE/TEE, where contrast injected in left arm vein results in opacification of LA followed by RA. These findings can be confirmed by cardiac MRI, cardiac CT, and cardiac catheterization [4].
There are few reports on the simultaneous presence of cor triatriatum and Raghib syndrome. It results in the PLSVC draining into lower chamber of LA which communicates with LAA and with RA through the ASD. It predominantly results in right to left shunt, resulting in cyanosis [5].
In our patient, there were two right to left shunts: from PLSVC to LA2 via unroofed coronary sinus and from RA to LA2 through the ASD due to the severe PAH, resulting in cyanosis and clubbing. As both the membranes in the LA were non-obstructive, there was delayed presentation of the patient in the fifth decade of life. Though there was presence of PLSVC with completely unroofed CS and definite right to left shunt from PLSVC to LA2 since birth, presence of associated supramitral ring diverted most of the systemic venous blood entering the middle LA chamber to the RA through the ASD; hence, our patient probably had no history of visible cyanosis before. However, once he developed Eisenmenger syndrome, he developed the second right to left shunt through the ASD resulting in visible cyanosis and clubbing.

Conclusion
This is the first case report describing the simultaneous presence of supramitral ring and cor triatriatum resulting in a new entity: "cor tetratriatum". Unlike cor triatriatum with Raghib syndrome, cor tetratriatum with Raghib syndrome presents late with cyanosis as the supramitral ring diverts most of the desaturated blood coming from PLSVC to LA to the RA and presents with cyanosis once Eisenmenger syndrome develops.