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Cor Triatriatum and Congenital Mitral Stenosis
Introduction
The main causes of congenital left atrial and ventricular inflow obstruction are pulmonary vein stenosis, cor triatriatum sinister (CTS), and mitral stenosis. Congenital pulmonary vein stenosis is usually a severe disease presenting in infancy with rare adult survival. This chapter focuses on CTS and congenital mitral stenosis.
Cor Triatriatum
Definition and Epidemiology
Cor triatriatum is a rare developmental anomaly in which a membrane divides the atrium and separates the pulmonary veins from the mitral valve (CTS) or, less commonly, the caval veins from the tricuspid valve (cor triatriatum dexter). CTS is believed to reflect failure of incorporation of the common pulmonary vein into the left atrium. This failure results in a variably obstructive membrane at the junction between these two embryologic structures, with a proximal chamber inclusive of the pulmonary veins and their confluence and a distal chamber reflecting the true left atrium and left atrial appendage.
CTS was first noted in the 1800s by Andral and Church ( Fig. 32.1 ), and termed “cor triatriatum” by Borst in 1905; it occurs in 0.1% of clinically diagnosed cases of congenital heart disease (CHD) and 0.4% of CHD autopsy cases. This discrepancy reflects the fact that most cases involve a nonobstructive membrane with questionable clinical relevance. The prevalence in the general population is likely to be less than 0.004%. Fewer than 350 cases have been reported since 1968. There may be a slight male predominance.
Embryology and Anatomy
The embryologic underpinnings of CTS remain unknown with debate focusing on three main hypotheses: malseptation, malincorporation, and entrapment. The malseptation hypothesis proposes that the membrane reflects abnormal growth and attachments of the septum primum. The malincorporation hypothesis proposes that the membrane represents the failure of complete fusion of the embryonic common pulmonary vein into the left atrium. This theory is appealing but does not readily explain the presence of morphologic atrial muscle fibers in the proximal chamber or that the fossa ovalis is located in the distal, true atrial chamber. The entrapment hypothesis suggests that the left horn of the sinus venosus entraps the common pulmonary vein, precluding its incorporation in the left atrium. It may be that CTS represents a common consequence of diverse embryologic misadventures, as none of the proposed mechanisms explains the full spectrum of reported anatomic variations and features.
Anatomic Variations and Classification
Regardless of the underlying embryology, in most instances the membrane lies above the fossa ovalis and left atrial appendage (LAA) and appears to be an extension of the “coumadin ridge.” Most commonly, the membrane is of the diaphragmatic type with a thin fibrous or fibromuscular membrane. Less common anatomic variations range from a tubular type, representing the unabsorbed tubular common pulmonary vein joining the left atrium, to an hourglass type intermediate between fibrous and tubular morphologies. There has even been one case reported of a branching membrane giving rise to “cor polyatriatum.”
The membrane in CTS is usually single, however, and characterized by one or more openings of variable size that allow communication between the proximal left atrium (PLA) located posterior-superiorly and the distal left atrium (DLA or true left atrium [LA]) located anterior-inferiorly. Subtotal CTS, in which the membrane attachment straddles, such that some of the pulmonary veins drain to the proximal chamber while the remaining pulmonary veins drain normally to the true LA, is rare.
Natural History and Presentation
The diagnosis may be made at any age. The degree of obstruction largely determines the age at symptomatic presentation, while diagnosis of a nonobstructive membrane is facilitated by advances in imaging technology. Variations in location, size of the orifice, presence of interatrial communication, and degree of lung damage due to chronic venous congestion give rise to varied clinical presentations.
Presentation in Childhood
Presentation in early life may vary from cardiogenic shock, pulmonary edema, respiratory distress, cyanosis, and pulmonary hypertension to mild shortness of breath on exertion or asymptomatic cardiac murmur. Hemoptysis may be a conspicuous and recurrent finding in patients with CTS. Most, though not all, cases of cor triatriatum that merit intervention are identified during childhood. Most patients with obstructive cor triatriatum die in infancy without treatment. In patients who develop pulmonary hypertension, the presence of a patent foramen ovale or ostium secundum atrial septal defect may allow selective decompression of the high-pressure right atrium due to the lower-pressure DLA, with resulting cyanosis. In rare cases, the interatrial communication may be between the right atrium and PLA, with a left-to-right shunt; this may prevent symptoms despite an importantly obstructive membrane ( Fig. 32.2 ).
Adult Presentation
CTS may present in adulthood with a wide range of severity in left ventricular inflow obstruction. Patients may present with symptoms and findings including cough, dyspnea on exertion, orthopnea, paroxysmal nocturnal dyspnea (PND), hemoptysis, pulmonary edema, chest pain, syncope, atrial fibrillation, and left atrial thrombus. The turbulent jet arising from the opening in an obstructive CTS membrane may produce jet lesions on the structurally normal mitral valve causing distortion or damage and secondary mitral regurgitation. Those with nonobstructive CTS may remain asymptomatic with normal survival and may be diagnosed incidentally during echocardiography, other imaging studies, evaluation for cryptogenic stroke, or during autopsy. It is very uncommon for the severity of obstruction to progress (eg, with calcification of the membrane), although symptoms may develop as a consequence of mitral regurgitation or atrial fibrillation.
Syndromes and Associated Defects
Cor triatriatum can present as an isolated lesion (classic), but it is more commonly seen in association with other congenital cardiac anomalies. These include patent foramen ovale or secundum atrial septal defect/aneurysm, patent ductus arteriosus, truncus arteriosus, atrioventricular septal defect, complete vascular ring, coarctation of the aorta, tetralogy of Fallot, transposition of the great arteries, persistent left superior vena cava, ostium primum atrial septal defect, ventricular septal defect, total or partial anomalous pulmonary venous drainage, and a variety of left-sided cardiac abnormalities including pulmonary vein atresia or stenosis noted in as many as 10% of cases in one series. Associated mitral valve lesions are sometimes congenital (Wong’s anomaly) or acquired. CTS has also been reported as a part of Silver-Russell syndrome, Shone complex, and Raghib complex. Skeletal abnormalities such as pectus excavatum may also be associated with CTS.
Diagnosis
Examination
Physical findings are not specific for CTS. There is a normal S1 with no opening snap, in contrast to valvar mitral stenosis. There may be tall jugular venous “a” waves, parasternal lift, loud P2, and diastolic rumble or continuous murmur with signs of pulmonary hypertension and hepatomegaly.
Electrocardiogram
In patients with obstruction, RV hypertrophy may be present. The frontal mean QRS axis is often between +120 and +140 degrees. Atrial fibrillation is also sometimes present. Apart from broad P waves, a consequence of left atrial dilation and hypertrophy, the rhythm and remainder of the electrocardiogram are otherwise usually normal.
Chest X-Ray
Symptomatic patients may have pulmonary venous congestion without left atrial enlargement and with normal cardiothoracic ratio in the absence of pulmonary arterial hypertension. Membrane calcification is rare.
Echocardiogram
The undulating CTS membrane may be seen on parasternal long, short, and apical 2- and 4-chamber views with movement toward the mitral valve in diastole and away in ventricular systole. Defining the relationship between the CTS membrane and the LAA allows differentiation from a supramitral ring. In CTS, the membrane is located superior to the LAA (between the LAA and pulmonary veins), while a supramitral ring is located inferior to the LAA and is often adherent to, and constitutes part of, the mitral valve leaflets ( Figs. 32.3 and 32.4 ). Two-dimensional imaging and Doppler imaging illustrate the size and location of the orifice(s) and degree of obstruction. High-frequency diastolic oscillations or fluttering of structurally normal mitral leaflets, due to turbulent flow, may be apparent. Flow across the defect is present throughout the cardiac cycle in CTS, but only during diastole in mitral stenosis. Transesophageal echocardiography may show a membrane extending from the coumadin ridge between the left lower pulmonary vein and the LAA. It is important to identify all pulmonary veins and their drainage. Three-dimensional (3D) echocardiography with color Doppler can be useful to further characterize the CTS and associated lesions. A prominent left atrial fold at the level of the coumadin ridge, persistent large left superior vena cava draining into the coronary sinus, and supramitral ring constitute important alternative diagnoses. High-velocity accelerating, aliasing, narrow Doppler flow with loss of phasic character, and a peak velocity greater than 1 m/s indicate hemodynamically important obstruction. Proximal obstruction may conceal a distal obstruction; coexisting mitral stenosis may be masked in the presence of obstructive CTS. Concomitant mitral regurgitation may give rise to a hemispheric or “helmet” sign due to containment of the mitral regurgitation jet in the DLA with bulging CTS membrane.
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