Cor Triatriatum Sinister is a rare congenital condition in which the left atrium is subdivided by a fibromuscular membrane into two distinct chambers, a posterosuperior and anteroinferior chamber. The pulmonary veins enter the posterosuperior chamber, also termed accessory LA chamber. The anteroinferior chamber, also referred to as the “true LA”, communicates with the mitral valve and gives rise to the LA appendage. The two chambers communicate through a membrane. The membrane that divides the atrium into two parts may vary significantly in size and shape. It may appear similar to a diaphragm or be funnel-shaped, bandlike or entirely intact (imperforate) or contain one or more openings (fenestrations) ranging from small, restrictive-type to large and unrestrictive. In addition, the accessory chamber may communicate with the right atrium through an anomalous channel. The most common form of cor triatriatum in one in which all four pulmonary veins drain to an accessory atrial chamber, but other more rare variants do exist in which there is partial or total anomalous pulmonary venous connection. The most widely accepted theory for the cause of cor triatriatum is secondary to an incomplete incorporation of the common pulmonary vein into the posterior aspect of the left atrium. Cor triatriatum is frequently associated with orther cardiac abnormalities such as a PFO, secundum ASD and left SVC to coronary sinus and less commonly with anomalous pulmonary venous connection. Symptoms are a result of the gradient across the dividing septum, which is secondary to the number and size of the fenestrations in the septum.
Represents 0.1-0.4% of all congenital abnormalities. Associated cardiac lesions include atrial septal defect, anomalous pulmonary venous return, bicuspid aortic valve and PDA.
Embryology and Genetics
Multiple proposed mechanisms which include: Abnormal growth of the septum primum, incomplete incorporation of the embryonic common pulmonary vein into the left atrium (most commonly accepted theory), entrapment of the common pulmonary vein by the left horn of the sinus venosus, thereby preventing its incorporation into the left atrium and persistence of the left superior vena cava that impinges on the developing left atrium
Accessory atrial chamber receives all pulmonary veins and communicates with left atrium
No other connections: classic cor triatriatum
Other anomalous connections
To RA directly
Accessory atrial chamber receives all pulmonary veins and DOES NOT communicate with left atrium
Anomalous connection to RA directly
Subtotal cor triatriatum
Accessory atrial chamber receives part of pulmonary veins and connects to LA
Remaining pulmonary veins connect normally
Remaining pulmonary veins connect anomalously
Accessory atrial chamber receives part of pulmonary veins and connects to RA
Remaining pulmonary veins connect normally
If no alternative pathway for accessory atrial chamber with stenotic opening to intra-atrial membrane results in elevated pressure in accessory atrial chamber which is transmitted to the pulmonary veins. Physiology is of pulmonary venous obstruction in severe cases with secondary pulmonary hypertension
Goals of Echocardiography Exam
2D echo is standard for diagnosis along with TEE in 3D for further characterization
Cor membrane is seen as a linear echodensity traversing the left atrial cavity
In the setting of a restrictive membrane you get secondary physiology of pulmonary venous obstruction with RA, RV and PA dilation, with secondary pulmonary hypertension and RV dysfunction
Assess RV/LV size and function
Assess for tricuspid regurgitation and peak TR velocity to estimate RVp
Assess pulmonary regurgitation (peak and end diastolic velocity) to assess peak and mean PA pressure
Assess septal configuration from parasternal short axis view to indirectly estimate RV pressure
Cor Triatriatum (CT) versus Supravalvar MV ring (SVMR)
CT: Linear echodensity, curvilinear and wind sock appearance moves toward MV in diastole and above the left atrial appendage
SVMR: Near atrial surface at base of mitral valve leaflets and relatively immobile usually adherent to MV and moves away in diastole
Left atrial appendage (and often the PFO) are located distal to membrane
Measure mean and maximal trans-membrane pressure gradients and maximal velocity by spectral Doppler
Mild pressure gradient across membrane may not reflect the high resistance across the circuit in the setting of a non restrictive superior ASD which may act as a “pop-off” decompressing the higher pressure pulmonary venous chamber into the lower pressure atrium. Therefore, in infancy these patients must be followed closely to ensure no interval restriction of membrane or atrial communication.
Chen Q, Guhathakurta S et al. Cor triatriatum in adults: three new cases and a brief review. Tex Heart Inst J. 1999: 26;206-210.
Moss and Adams. Heart disease in infants, children and adolescents including the fetus and young adult. 7th edition. 761-790.
Lai W, Mertens L, Cohen M, Geva T. Echocardiography in pediatric and congential heart disease from fetus to adult. 2009