Coronary Sinus Atrial Septal Defects
- Author: Louis I Bezold, MD; Chief Editor: Steven R Neish, MD, SM more...
Background
Coronary sinus atrial septal defects (ASDs) are defects located in the portion of the atrial septum that includes the coronary sinus orifice and are characterized by the absence of at least a portion of the common wall that separates the coronary sinus and the left atrium. Interatrial shunting occurs through the defect in the wall on the left atrial side, which is continuous with the orifice of the coronary sinus opening on the right atrial side of the septum. Coronary sinus defects make up a small subset of ASDs.
Coronary sinus defects are often associated with a persistent left superior vena cava (SVC) that drains into the coronary sinus. They may also be associated with complex congenital heart lesions in conjunction with heterotaxy syndrome, abnormalities of atrial situs, and other anomalies of systemic venous return. In a series of 25 patients with partial fenestrations of the coronary sinus the most common associated cardiac lesions were secundum ASDs, persistent left or right SVC and pulmonary atresia or tricuspid atresia.[1]
Coronary sinus ASDs are often difficult to diagnose and may even be overlooked during surgery for complex congenital heart disease.[1]
Anatomy
Coronary sinus ASDs are believed to arise from developmental failure of formation of the wall between the coronary sinus and the left atrium.
The coronary sinus is a systemic venous structure embryologically derived primarily from the left common cardinal vein that is continuous with the left anterior cardinal vein. Coronary sinus ASDs involve the inferior and anterior interatrial septa at the usual location of the orifice of the coronary sinus. The orifice of the coronary sinus becomes continuous with the left atrial chamber when a defect occurs in the wall separating the left atrium from the coronary sinus. This arrangement allows shunting between the atria.
From the right atrial aspect of the interatrial septum, the defect may consist of the coronary sinus orifice alone or with additional deficiency of atrial septal tissue around the coronary sinus orifice. On the left atrial side, the defect consists of partial or complete unroofing of the coronary sinus, if the entire superior aspect of the wall between the coronary sinus and the left atrium is absent.
Failure of the more cephalad portion of the embryologic left anterior cardinal vein to regress results in a persistent left SVC, which usually drains into the right atrium via the coronary sinus. A left SVC may connect to the left atrium directly if the coronary sinus is unroofed. An unroofed coronary sinus may be isolated or associated with an ASD.
Complete absence of the coronary sinus is common in atrial situs abnormalities with atrial isomerism, particularly right atrial isomerism. Atrial situs is an important feature with respect to abnormalities of systemic venous development, such as those observed in conjunction with coronary sinus ASDs. Defects are uncommon, and the coronary sinus is usually present in either atrial situs solitus or inversus (lateralized situs). SVC abnormalities are rare in atrial situs solitus but include left SVC to coronary sinus (prevalence approximately 3%) and, in rare cases, left SVC to the left atrium with coronary sinus unroofing.
Abnormal atrial situs with heterotaxy and atrial isomerism is associated with abnormality of atrial septation and venous connections. Abnormalities include bilateral SVC with variable presence of the coronary sinus in left atrial isomerism and bilateral SVC and common atrium with nearly universal complete absence of the coronary sinus in right atrial isomerism.
Pathophysiology
The pathophysiology of an isolated coronary sinus ASD is similar to that of a secundum ASD. Intrauterine physiology is unaffected. After birth, increases in pulmonary blood flow and left atrial pressure result in left-to-right shunting through the defect as the pulmonary resistance falls and the right ventricle becomes more compliant than before.
Right and left ventricular compliance primarily determine the direction and degree of shunting. At birth, compliance is similar in both ventricles, resulting in minimal shunting. As pulmonary vascular resistance falls, the right ventricle becomes progressively more compliant and the left-to-right shunt increases. Left ventricular compliance tends to decrease with age; this also promotes increased left-to-right flow. Minimal right-to-left shunting, predominantly from the inferior vena cava early in ventricular diastole or at the onset of ventricular systole, is observed in large ASDs.
The degree of atrial level shunting may be altered by the presence of associated cardiac lesions, pulmonary disease, or both. Magnitude and duration of atrial left-to-right shunting varies during normal respiration, increasing with expiration and decreasing with inspiration. Right-to-left shunting is affected in an inverse fashion. Pulmonary stenosis, pulmonary vascular disease, right ventricular hypertrophy, and pulmonary parenchymal disease increase the portion of the respiratory cycle with right-to-left flow and the magnitude of the shunt. Decreased left ventricular compliance due to left ventricular outflow tract obstruction or left ventricular hypertrophy increases left-to-right shunting. The severity of mitral stenosis may be underestimated in the presence of an ASD that partially relieves left atrial hypertension by means of increased left-to-right shunting.
ASDs with clinically significant left-to-right shunting cause the right atrium and ventricle to dilate, with some increase in thickness. The pulmonary arteries enlarge. Pulmonary vascular disease rarely develops. Leftward shift of the interventricular septum from right heart volume overload can result in mitral valve prolapse, mitral regurgitation, or both. Tricuspid annular dilation due to right ventricular dilation can worsen tricuspid regurgitation. Any other process causing right or left atrial enlargement can result in stretching of the ASD. Atrial dilatation may also play a role in the development of atrial arrhythmias (eg, atrial fibrillation or flutter).
Any ASD, including a coronary sinus defect, allows venous emboli to access the systemic arterial circulation whenever right atrial pressure exceeds left atrial pressure (paradoxical emboli).
Epidemiology
Frequency
United States
ASD, particularly ostium secundum ASD, is one of the most common congenital heart defects. The prevalence of ASDs of all types is approximately 0.2-0.6 cases per 1000 live births. Less than 1% of cases are of the coronary sinus type.
Mortality/Morbidity
Isolated coronary sinus ASDs are associated with a low rate of morbidity and mortality, similar to the rate observed in patients with isolated secundum ASDs. See Clinical.
- The size of the defect and the degree of shunting largely determine the symptoms. As with other types of ASDs, most children with isolated coronary sinus defects are asymptomatic. Morbidity or mortality due to atrial arrhythmias, chronic right-heart volume overload and heart failure, paradoxical emboli, or pulmonary hypertension (rare) are increasingly common with age beginning as early as the second to third decades of life.
- Morbidity and mortality rates are notably increased for most patients with coronary sinus ASDs and additional, complex congenital heart disease (eg, heterotaxy, splenic syndromes). Medical and surgical treatments for these patients vary and are largely determined by the severity of the associated congenital heart disease, which is usually of greatest hemodynamic significance. The prognosis and outcome largely depend on the type of congenital lesions present, the surgical interventions required, and the presence of splenic dysfunction.
- In most respects, the natural history of isolated coronary sinus ASDs is similar to that of secundum defects. Small defects that may remain undiagnosed result in no notable problems in childhood. Even some moderate-to-large defects do not cause clinically significant symptoms in childhood, although infants occasionally develop notable symptoms of congestive heart failure, generally in conjunction with additional contributing factors.
- Although patients with ASDs may be identified during infancy, the condition is frequently not recognized until childhood because of the absence of symptoms and the subtlety of the physical findings. ASDs associated with other, complex congenital cardiac defects are generally recognized early because of the presence of other hemodynamically significant abnormalities.
- In isolated defects, symptoms of left-to-right shunting and congestive heart failure worsen with age. The severity and onset of symptoms widely varies in adults and children. Some patients develop symptoms, such as exercise intolerance, may develop in the second decade of life, whereas others remain asymptomatic for several more decades.
- Large defects with significant atrial volume overload predispose patients to atrial arrhythmias (eg, atrial fibrillation or flutter, tachycardia). Atrial arrhythmias tend to increase with age (particularly >30 y) in unrepaired ASDs and are a major cause of morbidity and mortality. No correlation is proven between elevated pulmonary artery pressure and the incidence of atrial arrhythmias. Sinus bradycardia or junctional rhythm and atrioventricular block are reported in association with unrepaired secundum ASDs. Their prevalence with coronary sinus ASDs is unknown but likely similar to this. In some cases, cardiac rhythm disturbances may be due to associated complex cardiac anomalies, such as atrial situs abnormalities. In general, clinically significant arrhythmias are relatively rare in childhood.
- Pulmonary vascular disease, although rare, may develop in patients with unrepaired ASDs. This condition is extremely rare in childhood through early adulthood. Advanced pulmonary vascular disease is reported in children as young as 2 years, but no evidence suggests a cause-effect relationship versus the occurrence of an incidental ASD in a patient with primary pulmonary hypertension. Patients with large shunts may survive into the sixth or seventh decades of life without difficulty. Pulmonary vascular disease is most common in female individuals, in people at high altitudes (>4000 ft), and in elderly people. Pulmonary hypertension usually progresses, and the mortality rate is high with resistances of more than 15 Wood units regardless of medical or surgical treatment. Specific data regarding coronary sinus defects are limited, but the natural history is likely similar to that of other ASDs.
- Bacterial endocarditis is rare in the absence of associated abnormalities, and antibiotic prophylaxis is not recommended.
- Paradoxical emboli may occur, even with small ASDs, and they are a major reason to consider closure of the defect. Atrial fibrillation may be associated with atrial thrombi, which can embolize. Without surgery, coronary sinus ASDs with persistent left SVC may be associated with cerebral embolus and abscess due to right-to-left shunting. All of these events rarely occur in the pediatric age range.
- Most investigators report that many small ostium secundum ASDs close spontaneously. In contrast, data from one recent study suggested that ostium secundum defects of more than 3 mm in diameter often substantially enlarge over time and infrequently close.[2] To the author's knowledge, spontaneous closure of coronary sinus defects has not been reported.
Sex
The prevalence of ASDs, when all types are considered together, is higher in female individuals than in male individuals. The female-to-male ratio is approximately 2:1. However, the specific sex distribution for coronary sinus–type ASDs is unknown.
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