Background
Supracristal (or doubly committed) ventricular septal defect (VSD) is the least common type of VSD in the Western Hemisphere, accounting for approximately 5-7% of such defects in this part of the world, including in the United States. [1] The location of the supracristal VSD, with its close proximity to the aortic valve, accounts for the common development of aortic insufficiency with this defect. Left-to-right shunting of blood through the defect is believed to progressively pull aortic valve tissue (especially the right coronary cusp) through a Venturi effect (see the image below). (See Pathophysiology.)
Parasternal long-axis echocardiogram view showing supracristal ventricular septal defect (arrow) with buckling and prolapse (***) of the right coronary cusp of the aortic valve.
The crista supraventricularis can be considered synonymous with the infundibular (or conus) ventricular septum. It is the portion of the septum that separates the tricuspid and pulmonary valves. Defects above this part of the septum are referred to as supracristal defects. The term is generally reserved for defects lying immediately under the pulmonary valve. A defect, usually small, may occur within the conus septum and technically can be termed supracristal. (See Anatomy and Etiology.)
The spiraling course of the ventricular septum may make diagnosis of supracristal VSD more difficult. (See Presentation and Workup.)
Anatomy
The infundibular (or conus) septum separates the tricuspid and pulmonary valves and accounts for the more superior placement of the pulmonary valve relative to the aortic valve. This portion of the septum also provides fairly rigid, muscular support for the aortic valve, especially the right coronary cusp. [2]
Numerous synonyms indicate the confusion often associated with describing supracristal ventricular septal defects (VSDs). The term supracristal may be misleading because the entire conus septum (or a major portion of the septum) may be missing. The term is commonly used, however, emphasizing the superior location of the defect along with its close approximation to the aortic and pulmonary valve leaflets. Lack of support for the right aortic leaflet is crucial to the natural history of this type of VSD. [3]
The plane of the conus septum in the right ventricular outflow tract lies almost perpendicular to that of the remainder of the septum. From a surgical perspective, a defect lying in the conus septum may not be visualized from the standard right atriotomy approach, looking through the tricuspid valve. [2, 4]
Unlike the more common perimembranous type of VSD, the supracristal VSD does not lie near the tricuspid valve. Unless the supracristal defect is large, extending inferiorly to the perimembranous septum, the tricuspid valve is not involved in partial closure of the defect.
Conduction system tissue lies inferior to the supracristal VSD. The conduction system may lie closer to a larger defect that crosses from the outlet septum into the perimembranous area.
Pathophysiology
The natural history of supracristal ventricular septal defects (VSDs) depends on the location and size of the defect. Patients with small, isolated supracristal VSDs may have no symptoms or signs of congestive failure such as might be observed with a large shunt. [5] Progressive aortic insufficiency may develop later in life. Larger defects of the outlet septum frequently are associated with forms of aortic outflow obstruction (eg, coarctation, interrupted aortic arch). In such cases, symptoms of congestive heart failure and possible circulatory collapse appear early.
Patients with larger, isolated supracristal VSDs may develop congestive heart failure early in infancy due to a large left-to-right shunt. While spontaneous closure is not common, [6] a decrease in the magnitude of the left-to-right shunt may occur due to progressive prolapse into the defect of aortic valve tissue (the right coronary cusp or, possibly, the right sinus of Valsalva). [7] This valve leaflet prolapse is believed to result from the Venturi effect, as the high-velocity shunt flow produces negative pressure. Progressive distortion of the aortic leaflet or sinus as it prolapses into the VSD may lead to increasing aortic valve insufficiency.
Etiology
The muscular outlet septum is primarily formed from the proximal endocardial ridges (similar to endocardial cushion tissue). Semilunar valve tissue and the actual connection between the septum and the arteries are formed by the more distal endocardial ridges. Extracardiac mesenchyme, derived from neural crest tissue, condenses as prongs (which act as a welding agent) with the most superior portion of the distal cushions to form the aortopulmonary septum. [8] By exposing neural crest tissue to homocysteine, supracristal ventricular septal defects (VSDs) have been induced in a high percentage of chick embryos. Disruption of apoptosis and myocardialization has been proposed to explain these findings. [9]
The frequent association between arch abnormalities and significant conal VSDs suggests a common mechanism involving a chromosome band 22q11 microdeletion. Deletions in this area have not been linked with isolated supracristal VSDs. [10]
Epidemiology
Supracristal ventricular septal defect (VSD) accounts for approximately 5-7% of VSDs in the Western Hemisphere. [1] In the Eastern Hemisphere, however, the incidence of this condition is much higher, reaching 25% of all VSDs in patients from this part of the world, as supracristal VSDs are much more common in persons of Asian descent than in individuals of other races. Although the overall incidence of VSDs is no greater in Asians than in other groups, supracristal VSDs account for approximately 30% of VSDs in Asians. [1] Higher occurrence of the condition in this population has not been adequately explained, but one may assume that it is genetically determined.
Prognosis
The prognosis in patients with supracristal ventricular septal defect (VSD) should be considered good to excellent when the potential complication of aortic valve insufficiency is recognized and aggressively treated. [11, 12] Delayed recognition of or surgical treatment for progressive aortic valve insufficiency may lead to severe distortion of the aortic valve leaflet, making eventual valve replacement more likely. [13]
Morbidity or mortality in supracristal VSD is generally not the result of a large left-to-right shunt. Rather, it is caused by the development of aortic valve insufficiency. When progressive and severe, this results in left ventricular enlargement and eventual congestive heart failure, hence the admonition to address this problem early.
The appearance of aortic insufficiency as a complication of supracristal VSD is related to age. Young infants and toddlers presenting with supracristal VSDs are more likely to have findings of pulmonary overcirculation from the left-to-right shunt. While it may occur earlier in infancy, onset of aortic valve prolapse and progressive aortic insufficiency generally begins in children aged 6-10 years.
Patients with supracristal VSD are at increased risk of infective endocarditis. The risk is higher if aortic valve insufficiency is present.
Patient Education
The patient’s risk of developing infective endocarditis is higher for supracristal ventricular septal defect (VSD) with aortic insufficiency than it is for an isolated VSD. Patients and families should be educated on the importance of good oral and dental hygiene. Routine prophylaxis for dental or surgical procedures is no longer recommended unless there has been a prior episode of endocarditis. [14]
For patient education information, see the Heart Health Center, as well as Ventricular Septal Defect.
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Parasternal long-axis echocardiogram view showing supracristal ventricular septal defect (arrow) with buckling and prolapse (***) of the right coronary cusp of the aortic valve.
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Parasternal short-axis echocardiogram view with color Doppler showing proximity of ventricular septal defect jet to the pulmonic valves. The patient is an infant with neither aortic valve prolapse nor aortic insufficiency.
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Subcostal "right ventricular inflow/outflow" view showing the close relationship between the aortic and pulmonic valves in the presence of supracristal ventricular septal defect. Turbulent shunt flow is shown directed into the main pulmonary artery. The patient is an infant with neither aortic valve prolapse nor insufficiency.
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Transesophageal horizontal view of aortic root and right ventricle, showing sinus of Valsalva aneurysm leaking through a supracristal ventricular septal defect (VSD)(> <).
