Background
Cor triatriatum is a rare congenital cardiac anomaly in which a fibromuscular membrane divides the atrium in two. In its most common form, cor triatriatum sinister, the left atrium is divided into an upper chamber that receives the pulmonary veins and a lower chamber that is related to the left atrial appendage and the mitral valve orifice. [1]
The location of the atrial appendage is a key landmark in this congenital malformation. It differentiates cor triatriatum from a physiologically similar condition, supravalvular mitral stenosis. In cor triatriatum the left atrial appendage is invariably associated with the lower chamber, which is below the membrane.
Rarely, a fibromuscular membrane that is a remnant of the right valve of the sinus venosus divides the right atrium; this finding, so-called cor triatriatum dexter, is usually asymptomatic and is mostly reported as an incidental finding. [2] However, fetal right ventricular hypoplasia has been described associated with this anomaly and has been hypothesized to result from abnormal fetal circulation leading to growth restriction of the fetal right ventricle. [3] Owing to its clinical relevance, the remainder of this chapter focuses on cor triatriatum sinister.
Cor triatriatum represents 0.1% of all congenital cardiac malformations and may be associated with other cardiac defects in as many as 50% of cases. Examples of associated cardiac defects include atrial septal defect, persistent left superior vena cava with an unroofed coronary sinus, partial anomalous pulmonary venous connection, ventricular septal defect, and more complex cardiac lesions, such as tetralogy of Fallot, atrioventricular canal, double outlet right ventricle, and even transposition of the great vessels. [4] Associated bicuspid pulmonary valve, aortic valve atresia, and heterotaxy have also been described. [5]
In classic cor triatriatum, the pulmonary venous chamber receives all pulmonary veins and it drains into the left atrium through a variable-sized orifice. The natural history of this defect depends on the size of the communicating orifice between the upper and lower atrial chambers. If the communicating orifice is small, the patient presents critically ill and may succumb at a young age (usually during infancy) to congestive heart failure and pulmonary edema. If the connection is larger, patients may present in childhood or young adulthood with a clinical picture similar to that of mitral stenosis. Cor triatriatum may also be an incidental finding when it is nonobstructive.
Other anatomical variants of cor triatriatum include a pulmonary venous chamber that receives part of the pulmonary veins and communicates with the left atrium, and a pulmonary venous chamber receiving all or part of the pulmonary veins that does not connect with the left atrium.
Congenital pulmonary vein stenosis is a very rare association with cor triatriatum. [6] Variable types of subtotal cor triatriatum may be noted, with only the right or left pulmonary veins draining into the upper chamber. [7]
Pathophysiology
Initially, the fetal lungs and pulmonary veins are connected to the systemic venous circulation. Subsequently, a dorsal outgrowth from the common atria, also referred as common pulmonary vein, evaginates and joins the pulmonary veins, whereas the connection to the systemic circulation disappears. As the fetal heart grows, the common pulmonary vein is completely absorbed. Failure of this dorsal outgrowth to join the pulmonary veins results in total anomalous pulmonary venous drainage (TAPVD). An abnormal connection between the common pulmonary vein and the atria results in any of the variants of cor triatriatum.
The critical anatomic feature of cor triatriatum is a diaphragm that divides the left atrium into 2 chambers (see the videos below).
It consists of fibromuscular tissue, and the proximal chamber that is created represents a vestigial common pulmonary vein. The pulmonary veins thus drain into the proximal chamber.
Outcome depends on the size of the communication to the distal chamber, which communicates with the mitral valve. If present, a patent fossa ovalis or secundum atrial septal defect permits decompression of the proximal chamber into the right atrium.
The presentation of cor triatriatum is one of decreased cardiac output and pulmonary venous hypertension. If a connection between the common pulmonary venous chamber and the right atrium is present, pulmonary overcirculation may result in significant right ventricular enlargement.
Etiology
No known risk factors or associated genetic abnormalities have been reported with cor triatriatum.
Embryologically, the common pulmonary vein is normally absorbed and incorporated into the left atrium. Incomplete absorption results in a fibromuscular membrane that subdivides the left atrium into two chambers resulting in cor triatriatum.
Observation that a left superior vena cava is frequently associated with this lesion has led some to propose impingement of the left superior vena cava to the developing left atrium as a potential pathogenesis.
Epidemiology
United States data
Cor triatriatum is a very rare malformation. Incidence is approximately 0.1-0.4% of all infants with congenital cardiac disease.
Race-, sex-, and age-related demographics
No race predilection is reported, but a slight male predilection is observed, with a male-to-female ratio of 1.4:1.
The diagnosis is primarily made in infancy. Later presentation does occur but is usually in childhood or early adulthood; in this patient population, 85% are younger than 40 years. Rarely, patients presenting in their eighth or ninth decade of life have been reported.
Prognosis
Prognosis in symptomatic infants with cor triatriatum without surgical repair is poor with a mortality rate of 75%.
Presence of associated cardiac anomalies adversely affects prognosis.
If the connection between the proximal and distal chambers is not restrictive or if an atrial septal defect is present, prognosis is improved. In this subset of patients, the defect may escape detection in infancy and present later in life.
Mortality associated with surgery is primarily in the immediate postoperative period and patients that survive can expect a late mortality rate of less than 10% and a near normal life expectancy. Late survivors have essentially normal lifestyles without sequelae from the anomaly or surgical correction. The short-term, 30-day mortality rate is 15-20%. Recurrence of cor triatriatum has been described. [6]
Morbidity/mortality
Approximately 75% of patients die in infancy (generally from pulmonary hypertension) if the defect is unrepaired. If the communication between the proximal and distal chambers is not restrictive or if an atrial septal defect allows decompression of the hypertensive left atrium, the prognosis is significantly improved.
The only treatment is surgical correction. [8] Most postoperative deaths occur in the first 30 days. The early mortality rate in each large series was consistently 15-20%. Early deaths had a higher rate of associated severe cardiac anomalies.
Long-term results are excellent, with long term survival of 80-90% in patients surviving surgery. Survivors have excellent functional results without residual sequelae and a life expectancy that approaches that of the general population. This is particularly true when repair is performed in infancy.
Complications
If the condition is unrecognized and untreated, problems include pulmonary edema, right heart failure, and death. There are case reports of cor triatriatum causing shock infants in infants [9, 10, 11] and pulmonary hypertension in toddlers, [12] particularly in pediatric patients with other congenital heart anomalies.
Late complications include recurrence of the obstructive membrane with recurrence of symptoms. [6] Similar symptoms may occur later on in life if the membrane is incompletely excised.
Ischemic stroke as a late complication from undiagnosed cor triatriatum (sinister) in an adult has been described. [13, 14]
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Pediatric Cor Triatriatum. Long-axis parasternal view demonstrating a left atrial membrane separating pulmonary vein inflow from left ventricular (mitral valve) inflow. With permission from Michael Pettersen, MD, Pediatric Cardiology, Children's Hospital of Michigan, Detroit, MI.
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Pediatric Cor Triatriatum. Long-axis parasternal view depicting a two-dimensional image of cor triatriatum sinister membrane and a color Doppler image of pulmonary venous flow through the orifice of the membrane. With permission from Michael Pettersen, MD, Pediatric Cardiology, Children's Hospital of Michigan, Detroit, MI.
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Pediatric Cor Triatriatum. Short-axis parasternal view depicting right and left pulmonary vein flow proximal to the cor triatriatum left atrial membrane and left atrial appendage orifice distal to the cor triatriatum left atrial membrane. With permission from Michael Pettersen, MD, Pediatric Cardiology, Children's Hospital of Michigan, Detroit, MI.
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Pediatric Cor Triatriatum. Subxiphoid coronal image of the posterior left atrial chamber that receives pulmonary venous flow separated from the rest of the left atrium by the cor triatriatum membrane. With permission from Michael Pettersen, MD, Pediatric Cardiology, Children's Hospital of Michigan, Detroit, MI.
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Pediatric Cor Triatriatum. Apical five-chamber view demonstrating a 4-5 mm left atrial membrane orifice with mild pulmonary venous inflow restriction. Note the presence of an associated perimembranous ventricular septal defect (VSD) with tricuspid septal aneurysmal tissue. With permission from Michael Pettersen, MD, Pediatric Cardiology, Children's Hospital of Michigan, Detroit, MI.
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Pediatric Cor Triatriatum. This sonogram shows a mean Doppler gradient of 7-8 mmHg across the left atrial membrane indicating mildly elevated pulmonary venous pressures. With permission from Michael Pettersen, MD, Pediatric Cardiology, Children's Hospital of Michigan, Detroit, MI.
