Cor triatriatum is a rare congenital cardiac anomaly where an intra-atrial fibromuscular membrane divides the atrium. When the condition affects left atrium, it is known as cor triatriatum sinister. Most of the adults who have cor triatriatum sinister have a large fenestration in the intra-atrial membrane. Such a large fenestration renders them symptom free till calcification or stiffening of the intra-atrial membrane happen following which they may present with pulmonary hypertension and/or pulmonary congestion. We here present a case of cor triatriatum sinister; the right pulmonary veins were noted to drain into the accessory atrium while the left pulmonary veins drained into the true atrium

A 52 year-old-woman with a past medical history of morbid obesity, diabetes mellitus and obstructive sleep apnea presented for evaluation of severe progressive dyspnea and decrease in exercise tolerance. On examination vitals were stable, cardiac auscultation revealed a loud P2 without an opening snap. A transthoracic echocardiogram revealed normal left ventricular size and function, marked right atrial and right ventricular enlargement with severe tricuspid regurgitation. Pulmonary artery systolic pressures (PASP) were estimated to be 105 mm of Hg. Given her symptomatology, the patient was immediately sent for a computer tomography angiography (CTA) of the chest to rule out pulmonary embolism. The study revealed chronic hypoplasia of the right lung vasculature with a subtotal cor triatriatum (Image), which drained both right pulmonary veins. The left-sided pulmonary veins drained into the main left atrium without obstruction. Cardiac catheterization revealed elevated right sided pressures with a PASP of 117 mmHg. The patient died of intracranial hemorrhage before surgical resection of the intra-atrial membrane.

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Figure 1. CT angiography of the chest showing cor triatriatum sinister (indicated by red arrow).

Cor triatriatum (triatrial heart) is a rare congenital abnormality that accounts for 0.1% of clinically diagnosed cardiomyopathies and 0.4% of congenital heart diseases in autopsy studies [1, 2]. Cor triatriatum (CorT) has no sex, race or genetic predilection; Cor triatriatum of left atrium (cor triatriatum sinister) (CTS) is common than the right (cor triatriatum dexter) [4]. Cor triatriatum is associated with other congenital cardiac abnormalities in 80% of the cases. Such associated congenital abnormalities include anomalous pulmonary venous return, atrial septal defect, bicuspid aortic valve, bicuspid right atrioventricular valve, coarctation of aorta, common atrioventricular canal, double outlet right ventricle, hypoplastic mitral valve, persistent left superior vena cava with unroofed coronary sinus,tetralogy of fallot and ventricular septal defect [4].

In CTS, a thick fibromuscular membrane divides left atrium into proximal or superior accessory chamber and a distal or true atrial chamber. The shape of such a fibromuscular band can be transverse, band-like or funnel-shaped [4]. The accessory atrium usually receives the pulmonary veins, the true atrium is in contact with mitral valve and is in continuum left atrial appendage and true atrial septum [11]. Many embryological theories of the origin of CTS have been proposed, none of which has been fully established. These theories have been tabulated in Table 2.

Several classification of CTS has been proposed. Loeffler CTS classification is the earliest (1949) and the simplest of all; this classifications system is based on the number and size of fenestration in the intra-trial fibromuscular membrane. Loeffler CTS classification has been summarized in Table 3 [9]. The basis of other classification systems has been tabulated in Table 4 [13, 15-17].

Clinical presentation of CTS is directly dependent on the size of the fenestration of the intra-atrial membrane between the accessory and true atrium. Loeffler’s group I and II CTS usually present newborns and infants; these patients presents with neonatal respiratory distress and have a high mortality rate [18]. Loeffler’s group III CTS usually presents in adulthood; the large fenestration renders the condition asymptomatic in early life [19]. Symptoms in younger adults result from obstruction of the mitral valve. Much later in adult life calcification and fibrosis lead to stiffening of the intraatrial membrane and subsequent symptomatology [20]. Symptoms like exertional dyspnea, orthopnea, and hemoptysis develop secondary to pulmonary congestion and/or pulmonary hypertension [4]. Young adult females with undiagnosed CTS develop severe pulmonary edema [21, 22]. CTS may also cause atrial fibrillation; intra-atrial thrombus formed secondary to atrial fibrillation may embolize to cause systemic thromboembolism or stroke [4]. Physical examination in patients with CTS may reveal a loud P2 and a mid-diastolic murmur; signs of pulmonary congestion may be present. CTS might be confused for mitral stenosis which can be differentiated due to the absence of a loud S1 and opening snap [4].

Electrocardiography in CTS may show right ventricular hypertrophy, right axis deviation and S1Q3 pattern secondary to pulmonary hypertension. Associated atrial arrhythmias may also be evident. A Transthoracic echocardiogram is the initial imaging modality employed in the evaluation of suspected CTS cases [23]. Transesophageal echocardiogram (TEE) is more specific and helps to confirm the diagnosis [4]. The 3D fully-sampled matrix array TEE (3D-MTEE) transducer can provide real-time imaging and is more accurate in the visualization of posterior structures of the heart [4]. Computed tomography and magnetic resonance imaging are other options that aid in the diagnosis of CTS. Cine MRI can also show the flow turbulence in CTS [21, 22]. Ineffective use of imaging may result in labeling of CTS as primary pulmonary hypertension or mitral stenosis. Imaging studies are important to

understand the nature of CTS and other possible associated cardiac defects before attempted correction [4].

Asymptomatic patients with CTS and incidentally found CTS do not need any treatment. Pulmonary congestion secondary to CTS is managed with preload reduction with diuresis and digoxin [4]. Catheter ablation for atrial arrhythmias associated with CTS has been reported [25, 26]. The definitive treatment is surgical repair of CTS. The repair may be performed by left or right atrial approach. Following surgery, excellent outcomes are noted, and five-year survival rates are greater than 90% [19, 27].The CTS patient presented here had chronic hypoplasia of the right lung vasculature with a subtotal CTS. The left pulmonary veins drained into the main left atrium and as a result, there was no hypoplasia of the vasculature. This variant of CTS is extremely unusual. It is important to keep CTA in the differential when patients present with significant pulmonary hypertension as it is a potentially curative with excellent five-year survival rates after surgical repair.

CTS is a rare congenital cardiac abnormality which is almost always associated with a variety of other congenital cardiac abnormality. Symptomatology in CTS depends on the size of the fenestration in the intra-atrial membrane. Loeffler’s group I and II CTS presents in neonates and infants with severe respiratory distress and are associated with high mortality. Loeffler’s group III CTS is noted in adults in whom symptoms appear secondary to obstruction of the mitral valve by intra-atrial membrane or calcification and stiffening of the intra-atrial membrane. Non-invasive imaging with transthoracic echocardiogram is the initial imaging study of choice. TEE and 3D-MTEE are better in the visualization of anatomy. Surgical correction carries excellent prognosis and is the definitive treatment of choice.