9.6 Cor Triatriatum, Systemic Venous Anomalies & Heterotaxy Syndromes
Key Takeaways
- Cor triatriatum sinister is distinguished from a supravalvar mitral ring by the position of the left atrial appendage and fossa ovalis: in cor triatriatum both lie in the distal (mitral) chamber below the membrane, whereas a supravalvar mitral ring sits below the appendage and immediately above the mitral valve.
- Persistent left superior vena cava is the most common systemic venous anomaly and is suspected whenever a dilated coronary sinus is seen in the parasternal long-axis view; agitated saline injected in the LEFT arm confirms it by opacifying the coronary sinus before the right atrium.
- Interrupted inferior vena cava with azygos continuation is identified in the subcostal transverse view as a dilated azygos vein lying posterior and adjacent to the descending aorta, with hepatic veins draining directly into the right atrium; it is strongly associated with left atrial isomerism.
- Right atrial isomerism (asplenia, Ivemark syndrome) shows the abdominal aorta and inferior vena cava on the SAME side of the spine in the subcostal transverse view and clusters with totally anomalous pulmonary venous connection, atrioventricular septal defect, single ventricle, and pulmonary outflow obstruction.
- Left atrial isomerism (polysplenia) is characterized by interrupted inferior vena cava with azygos continuation, atrioventricular septal defect, partial anomalous pulmonary venous connection, and sinus node dysfunction with bradycardia or complete heart block.
9.6 Cor Triatriatum, Systemic Venous Anomalies & Heterotaxy Syndromes
Clinical Core: Three separate ARDMS tasks converge here: cor triatriatum (3.A.19), anomalies of the systemic venous system (3.A.17), and anomalies of abdominal and cardiac situs and position (3.A.16). They belong together because all three are answered from the same two acoustic windows. The subcostal transverse abdominal sweep establishes situs and the venous return, and the parasternal long axis with the coronary sinus in view flags the most common systemic venous anomaly in medicine. A pediatric sonographer who begins every study with these two looks will almost never be surprised later.
Cor Triatriatum Sinister
Cor triatriatum sinister results from failure of incorporation of the common pulmonary vein into the left atrium, leaving a fibromuscular membrane that divides the left atrium into two chambers.
- Proximal (posterosuperior) chamber: receives all four pulmonary veins. This is the embryologic common pulmonary vein.
- Distal (anteroinferior) chamber: the true left atrium, containing the left atrial appendage, the fossa ovalis, and the mitral valve.
- Flow between them passes through one or more restrictive fenestrations in the membrane.
The Landmark That Settles the Diagnosis
The single most tested discriminator is the position of the left atrial appendage relative to the membrane:
| Lesion | Membrane position | Appendage and fossa ovalis | Mitral valve |
|---|---|---|---|
| Cor triatriatum sinister | Above the appendage | In the distal chamber, below the membrane | Structurally normal |
| Supravalvar mitral ring | Below the appendage, immediately above the mitral annulus | Above the ring | Often abnormal; part of the Shone complex |
Get this wrong and the surgical plan changes, because cor triatriatum is cured by membrane resection with a normal mitral valve, while a supravalvar ring typically accompanies multilevel left heart obstruction.
Imaging and Hemodynamics
- Best windows: apical four-chamber and subcostal four-chamber, with the parasternal long axis useful for the appendage relationship. Transesophageal echocardiography resolves ambiguous cases.
- Two-dimensional: a linear echodensity crossing the left atrium. It must be distinguished from a prominent left atrial ridge (the "coumadin ridge") between the left upper pulmonary vein and the appendage, and from a normal left atrial ridge or a redundant fossa ovalis flap.
- Color Doppler: flow acceleration and aliasing at the fenestration, which also localizes the orifice for the spectral cursor.
- Spectral Doppler: a continuous, high-velocity, non-phasic signal across a restrictive orifice, and a raised mean diastolic gradient, exactly mimicking mitral stenosis or pulmonary vein obstruction. The distinguishing feature is that the mitral inflow recorded distal to the membrane is normal.
- Downstream consequences: pulmonary venous hypertension, elevated right ventricular systolic pressure estimated from the tricuspid regurgitant jet, right ventricular hypertrophy, and, in severe neonatal cases, a presentation indistinguishable from obstructed totally anomalous pulmonary venous connection.
- Associations: atrial septal defect (which may decompress the proximal chamber if it communicates with it), partial anomalous pulmonary venous connection, and persistent left superior vena cava.
Cor Triatriatum Dexter
The right-sided counterpart is persistence of the right valve of the sinus venosus, which partitions the right atrium into a smooth-walled posterior portion receiving the venae cavae and coronary sinus and a trabeculated anterior portion containing the appendage and tricuspid valve. It sits on a continuum with the Chiari network and a prominent eustachian valve, which are common benign variants, and it can direct inferior vena caval flow across a patent foramen ovale to produce unexplained cyanosis.
Anomalies of the Systemic Venous System
Persistent Left Superior Vena Cava (PLSVC)
The most common systemic venous anomaly, present in roughly 0.3% to 0.5% of the general population and in a considerably higher fraction of children with congenital heart disease.
- The left anterior cardinal vein fails to regress, descending anterior to the left hilum, in the atrioventricular groove, to drain into the coronary sinus and then the right atrium.
- Sentinel two-dimensional finding: a dilated coronary sinus seen in the parasternal long axis posterior to the left atrioventricular groove, and confirmed in the apical four-chamber view angled posteriorly.
- Suprasternal or high left parasternal short-axis imaging shows the vertical vein lateral to the left pulmonary artery and anterior to the left pulmonary veins.
- Confirmation: agitated saline injected into the left arm opacifies the coronary sinus before the right atrium. A right arm injection opacifies the right atrium first and will miss the diagnosis entirely.
- Unroofed coronary sinus: when the wall between the coronary sinus and the left atrium is deficient, the persistent left superior vena cava drains into the left atrium, producing a right-to-left shunt and systemic desaturation, and agitated saline from the left arm appears in the left atrium. This is a surgically important variant and is the fourth type of atrial septal defect.
- Practical consequences: complicates cardiopulmonary bypass venous cannulation and retrograde cardioplegia, complicates central line and pacing lead placement, and mandates a bilateral bidirectional Glenn in a single-ventricle patient.
Interrupted Inferior Vena Cava with Azygos Continuation
- The hepatic segment of the inferior vena cava fails to form; infrarenal caval blood ascends through a dilated azygos (or hemiazygos) vein to the superior vena cava.
- Subcostal transverse view: instead of the normal single inferior vena cava anterior and to the right of the aorta, two similar-caliber vessels lie adjacent to the spine, with the azygos vein directly posterior or posterolateral to the descending aorta — the classic "double vessel" sign.
- Hepatic veins drain directly into the right atrium through a separate confluence.
- Strongly associated with left atrial isomerism (polysplenia).
- A subcostal or femoral venous approach to the heart is impossible, which changes catheterization and Fontan planning.
The Rest of the Catalogue
| Anomaly | Echocardiographic signature |
|---|---|
| Bilateral superior venae cavae | Right SVC plus PLSVC, with or without a bridging innominate vein |
| Absent right superior vena cava | Isolated PLSVC to coronary sinus with no right-sided cava |
| Retro-aortic innominate vein | Innominate vein courses posterior to the ascending aorta; common with conotruncal anomalies |
| Levoatriocardinal vein | Decompressing vein from the left atrium to a systemic vein in severe left heart obstruction with a restrictive atrial septum |
| Anomalous hepatic venous drainage | Hepatic veins to the left-sided atrium; a cause of persistent cyanosis after the Kawashima operation |
| Coronary sinus atresia or ostial stenosis | Dilated coronary sinus without a PLSVC; drainage via a PLSVC or via thebesian veins |
Abdominal and Cardiac Situs
Situs determination is the first step of sequential segmental analysis and is performed in a subcostal transverse view at the level of the diaphragm, with the transducer index oriented to the patient's left and the operator deliberately establishing patient left and right on the image before interpreting anything.
| Situs | Aorta | Inferior vena cava | Stomach / liver |
|---|---|---|---|
| Solitus (normal) | Left of and posterior to the spine | Right of and anterior to the spine | Stomach left, liver right |
| Inversus (mirror image) | Right of the spine | Left of the spine | Stomach right, liver left |
| Right isomerism | Aorta and IVC on the SAME side of the spine, IVC anterior to the aorta ("juxtaposition") | Midline liver, variable stomach | |
| Left isomerism | Aorta anterior and to one side | IVC interrupted; azygos posterior to the aorta | Midline liver, variable stomach |
Cardiac position (levocardia, dextrocardia, mesocardia) and cardiac apex direction are reported separately from situs, because the two can be discordant: situs solitus with dextrocardia (isolated dextrocardia) carries a very high incidence of complex congenital heart disease, whereas situs inversus with dextrocardia (mirror-image dextrocardia) is frequently associated with a structurally normal heart and with primary ciliary dyskinesia in Kartagener syndrome.
Heterotaxy: The Two Isomerisms
| Feature | Right atrial isomerism (asplenia, Ivemark) | Left atrial isomerism (polysplenia) |
|---|---|---|
| Bilateral morphology | Bilateral right-sidedness | Bilateral left-sidedness |
| Spleen | Absent; Howell-Jolly bodies on blood smear; infection risk requiring prophylaxis | Multiple small spleens |
| Lungs / bronchi | Bilateral trilobed lungs, bilateral eparterial bronchi | Bilateral bilobed lungs, bilateral hyparterial bronchi |
| Systemic veins | Bilateral superior venae cavae; IVC and aorta same side of the spine | Interrupted IVC with azygos continuation |
| Pulmonary veins | Totally anomalous pulmonary venous connection, frequently infracardiac and obstructed | Partial anomalous pulmonary venous connection; veins to both atria |
| Intracardiac | Complete atrioventricular septal defect, single ventricle, transposition or double outlet right ventricle, pulmonary stenosis or atresia, common atrium | Atrioventricular septal defect, ventricular septal defect, double outlet right ventricle; outflow obstruction less common |
| Rhythm | Twin sinus nodes; ectopic atrial rhythm | Absent or hypoplastic sinus node — bradycardia, ectopic atrial rhythm, congenital complete heart block |
| Presentation | Severe neonatal cyanosis; often single-ventricle palliation; poor prognosis | More variable; may present later; biventricular repair more often feasible |
A practical bedside rule the exam rewards: profound neonatal cyanosis with obstructed pulmonary venous return and a single ventricle points to right isomerism; an interrupted inferior vena cava with bradycardia points to left isomerism.
Exam-Day Traps
- Injecting agitated saline in the right arm to look for a persistent left superior vena cava. The left arm is the only injection that answers the question.
- Assuming a dilated coronary sinus always means PLSVC. Elevated right atrial pressure, an unroofed coronary sinus, coronary sinus ostial atresia, and a coronary artery fistula draining to the coronary sinus all dilate it as well.
- Calling every linear left atrial echo a cor triatriatum membrane. Find the appendage; a membrane above it is cor triatriatum, a membrane below it is a supravalvar mitral ring, and a stubby structure between the left upper pulmonary vein and the appendage is the normal left atrial ridge.
- Reporting situs from the apex direction. Apex direction is cardiac position, not situs; situs comes from the subcostal transverse abdominal relationship of the aorta and inferior vena cava.
- Forgetting the hemodynamic follow-through. Any obstructive left atrial membrane requires an estimated right ventricular systolic pressure from the tricuspid regurgitant jet, because that number is what conveys urgency.
A 3-year-old presents with exertional dyspnea and recurrent respiratory infections. Apical four-chamber imaging shows a linear membrane crossing the left atrium with turbulent, continuous high-velocity flow through a small central orifice and a mean gradient of 9 mmHg. The mitral valve leaflets and subvalvar apparatus are structurally normal. Which anatomic relationship confirms cor triatriatum sinister rather than a supravalvar mitral ring?
A neonate has a dilated coronary sinus on the parasternal long-axis view. Agitated saline is injected through a left antecubital line and the coronary sinus does not opacify; instead the left atrium fills with microbubbles before the right atrium. What does this establish?
On the subcostal transverse sweep of a cyanotic neonate, two vessels of similar caliber lie adjacent to the spine, with the more posterior vessel positioned directly behind the descending aorta. The hepatic veins are seen entering the atrium through a separate confluence, and the electrocardiogram shows a slow ectopic atrial rhythm. Which diagnosis does this constellation indicate?
Why must the abdominal aorta and inferior vena cava be identified in the subcostal transverse plane before the cardiac segments are described, rather than inferring situs from the direction the cardiac apex points?