AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

Section 2 of 11  

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Background

Supracristal (or doubly-committed) ventricular septal defect (VSD) is the least common type of VSD in the western hemisphere. Its location adjacent to the pulmonary and aortic valves accounts for the unique natural history associated with this defect. The spiraling course of the ventricular septum may make diagnosis of the supracristal VSD more difficult.

Definition

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 in this part of the septum generally are referred to as supracristal defects. The term generally is reserved for defects lying immediately under the pulmonary valve, so that aortic and pulmonary valve tissue are in fibrous continuity and not separated by septal tissue.

Embryology

The muscular outlet septum is formed primarily from the proximal endocardial ridges (similar to endocardial cushion tissue). Semilunar valve tissue and the actual connection between the septum and the arteries is 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. Recently, by exposing neural crest tissue to homocysteine, supracristal ventricular septal defects have been induced in a high percentage of chick embryos. Disruption of apoptosis and myocardialization has been proposed to explain these findings.

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.

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 muscular fairly rigid support for the aortic valve, especially the right coronary cusp.

Numerous synonyms indicate the confusion often associated with describing this particular type of ventricular defect. The term supracristal may be misleading because the entire conus septum (or a major portion of the septum) may be missing. However, the term is used commonly and underscores the superior location of the defect along with the close approximation of the aortic and pulmonary valve leaflets.

The lack of support for the right aortic leaflet is crucial to the natural history of this type of VSD.

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.

Unlike the more common perimembranous type of VSD, 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.

Natural history

The natural history of supracristal VSDs depends on the location and size of the defect.

Patients with small isolated supracristal VSDs may have no early symptoms or signs (eg, congestive failure) such as would be observed with a large shunt. Progressive aortic insufficiency may develop late in the first decade of life. However, larger defects of the outlet septum frequently are associated with severe 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 show early signs of decompensation from a large left-to-right shunt. Because these defects are not surrounded by muscular tissue, spontaneous closure is less common. However, the defect may decrease in size by progressive prolapse of aortic valve tissue (the right coronary cusp or, possibly, the right sinus of Valsalva). This valve prolapse is believed to result from negative pressure by shunt flow because of the Venturi effect. This progressive distortion of the aortic leaflet or sinus may lead to increasing aortic valve insufficiency or to formation of an aneurysm in the sinus of Valsalva.

Pathophysiology

The unique location of the supracristal ventricular septal defect with its close proximity to the aortic root 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.

Frequency

United States

VSDs account for approximately 25-30% of significant congenital heart disease. Of these, approximately 4-5% are supracristal VSDs. These rates are similar throughout the Western Hemisphere.

International

Supracristal VSDs are much more common in persons of Asian descent than in individuals of other races. Supracristal VSDs account for approximately 25% of all VSDs in patients from the Eastern Hemisphere.

Mortality/Morbidity

Morbidity/mortality is generally not the result of large left-to-right shunt. Rather, it is caused by progressive development of aortic valve insufficiency, with development of left ventricular enlargement and eventual congestive heart failure if the problem is not addressed early enough.

Race

Although the overall incidence of VSDs is no higher in Asians than in other groups, supracristal VSDs account for approximately 25% of VSDs in Asians and only approximately 5% of VSDs in other groups. The higher occurrence of supracristal VSDs in Asians has not been explained adequately.

Sex

No predilection based on sex exists.

CLINICAL

Section 3 of 11  

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History

• Symptoms and their severity are a function of size and location of the defect, the relative systemic and pulmonary vascular resistances, and presence of associated abnormalities. Symptoms may range from severe congestive failure and cardiogenic shock in patients with large conal defects and left heart obstruction to complete absence of symptoms in patients with small isolated defects.
• Exercise intolerance and dyspnea suggest progressive aortic insufficiency, although early detection and treatment for valve insufficiency should obviate any significant symptoms.

Physical

Because congestive heart failure is unusual in the patient with a small supracristal VSD, general examination findings should be normal, with no signs of respiratory distress or growth failure. Infants with larger defects, especially with associated left ventricular outflow obstruction (eg, doubly committed subarterial defect with interrupted aortic arch), may present within the first week of life with profound congestive heart failure and cardiogenic shock.

• The murmur from a supracristal VSD is systolic and located at the upper left sternal border (ie, second or third intercostal space). The murmur is often crescendo-decrescendo in character, unlike the holosystolic regurgitant murmur of VSDs in other locations of the septum. It may radiate laterally and posteriorly owing to shunt flow directed into the pulmonary outflow tract.
• When a patient is known to have a supracristal VSD, the examination should focus on whether aortic insufficiency is present. A high-pitched diastolic murmur beginning with the second heart sound may be heard along the left sternal border. The combined systolic and diastolic murmurs may be likened to the sound of sawing wood.
• • The systolic-diastolic murmur of supracristal VSD with aortic insufficiency may be confused with a continuous murmur (eg, patent ductus arteriosus, arteriovenous malformation or fistula).
  • Maneuvers to increase the diastolic murmur of aortic insufficiency include isometric handgrip, leaning forward in a sitting position, and holding the breath during expiration.
  • With increasing severity of aortic insufficiency, pulse pressure (ie, difference between systolic and diastolic blood pressures) and pulse intensity may increase.

DIFFERENTIALS

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WORKUP

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Imaging Studies

• Chest x-ray
  • The chest x-ray may be normal in infancy if no large left-to-right shunt is present. If a large shunt is present, cardiomegaly (left heart enlargement, both left atrium and left ventricle) with increased pulmonary vascularity from increased pulmonary blood flow may be observed.
  • The x-ray of the older child or adult with progressive aortic insufficiency may show left heart enlargement (particularly left ventricular enlargement) and prominence of the ascending aorta. Shunt volume generally is smaller, thus pulmonary vascularity generally is normal unless advanced left heart failure produces pulmonary edema.
• Two-dimensional transthoracic echocardiography and color Doppler echocardiography
  • Echocardiography (ECHO) provides the most efficient means to diagnose supracristal VSD accurately and the most effective means to monitor progressive aortic insufficiency. An accurate diagnosis generally can be made in infants and children with standard transthoracic ECHO examination. In the older child and adult, transthoracic ECHO may be inconclusive; in such cases, transesophageal ECHO may be extremely helpful.
  • Two-dimensional imaging shows the supracristal VSD in the parasternal short-axis view or the modified apical 3-chamber view (ie, left atrium, left ventricle, aortic root, and pulmonary root, equivalent to the transesophageal view with transducer at 90° degrees). The defect also can be observed well in the subcostal parasagittal view (ie, visualizing the pulmonary and aortic outflow tracts). However, the supracristal VSD cannot be imaged from the apical 4-chamber view because of the orientation of the outlet septum. Distortion of the right aortic leaflet may be the only clue to the presence of a significant supracristal VSD because the aortic leaflet may "plug" the defect.
• • Color Doppler examination, using the parasternal short-axis view, detects left-to-right shunting with turbulent flow directed into the pulmonary outflow tract and often across the pulmonary valve. This turbulence may be confused with pulmonary stenosis; however, careful slow-motion review of color flow results (with electrocardiographic timing) may show early appearance of turbulent flow below the pulmonary valve.
  • The best way to detect aortic insufficiency is by color Doppler in the parasternal long-axis and the apical 5-chamber views. The modified apical 3-chamber view also can be used to detect left-to-right shunting and aortic insufficiency. Numerous methods are available to provide semiquantitative information on the severity of aortic insufficiency (eg, color jet–to–outflow width ratio, pressure half time).
  • The best way to identify progression of aortic insufficiency is by serial comparison of left ventricular systolic and diastolic dimensions and ventricular function (shortening fraction or ejection fraction). Progressive left atrial enlargement can be a sign of ventricular diastolic dysfunction.
• Angiography
• • The supracristal VSD is defined best in the right anterior oblique projection or the cranially tilted left anterior oblique projection. Small supracristal defects may not be identified in the standard long-axial oblique projection because of rotation of the septum. Direct continuity between the aortic and pulmonary valves is the hallmark of the supracristal type of ventricular defect. Larger defects may extend inferiorly into the perimembranous septum and sometimes through to the inlet septum.
  • Distortion of the aortic valve cusp or root may be the only clue to a significant supracristal VSD, and the apparent volume of left-to-right shunt into the pulmonary outflow tract may be small.
• Magnetic resonance imaging: MRI may be used with appropriate projections and alignment to show the pulmonary outflow tract. Serial MRI studies can be helpful in that they do not expose the patient to ionizing radiation. Blood flow studies can be used to provide quantitative information on regurgitant volume in the assessment of aortic insufficiency.

Other Tests

• Electrocardiogram
• • ECG findings may be normal in infancy because the defect may not be large enough to cause a significant left-to-right shunt and ventricular hypertrophy. With larger defects, the ECG may show left atrial enlargement and left and right ventricular hypertrophy.
  • With progressive aortic insufficiency in the older child or adult, the ECG usually shows evidence of left heart enlargement from volume overload (ie, left atrial enlargement and left ventricular hypertrophy [tall R waves in the left precordium with or without ST-T changes]).

Procedures

• Cardiac catheterization
• • Catheterization is helpful in quantifying shunt volume and pressure resistance. Step-ups in oxygen saturation often are detected in the pulmonary artery rather than in the right ventricular cavity. This may be because of streaming of the shunted blood into the pulmonary outflow tract.
  • If aortic valve prolapse is significant, left-to-right shunting by oximetry may be fairly unremarkable because the VSD in such cases is partially closed.
  • Postcatheterization precautions include hemorrhage, vascular disruption after balloon dilation, pain, nausea and vomiting, and arterial or venous obstruction from thrombosis or spasm.
  • Possible complications include rupture of blood vessel, tachyarrhythmias, bradyarrhythmias, and vascular occlusion.

TREATMENT

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Medical Care

Once the diagnosis of supracristal VSD has been made, carefully monitor patients for development of aortic insufficiency. This necessitates not only periodic physical examination with auscultation but also serial echocardiograms and Doppler echocardiograms because these diagnostic studies are more sensitive than auscultation in detecting valve regurgitation.

Surgical Care

Because spontaneous closure is uncommon in supracristal VSDs, and because aortic insufficiency is a common complication, surgical closure is recommended in most cases. Aortic insufficiency in supracristal VSD usually is progressive and warrants an aggressive approach with early intervention to avoid aortic valve deformity and replacement. Aortic insufficiency caused by supracristal VSD must be differentiated from that caused by an abnormal aortic valve (usually a bicuspid valve); surgical intervention usually is delayed in the latter disorder because the abnormal aortic valve typically requires replacement rather than repair in cases of aortic insufficiency.

• Because of the orientation of the right ventricular outflow tract, the standard surgical approach from the right atrium does not allow adequate visualization of the ventricular defect. Incision into the main pulmonary artery, which exposes the defect through the pulmonic valve, has proved successful. Repair may be achieved with patch or suture closure, depending on the size of the defect. Aortic valvuloplasty is often, but not always, necessary, and incision through the aortic root can allow adequate visualization for valve repair (Trusler technique). The approach through the main pulmonary artery avoids the need for incision into the right ventricle. Care should be taken to avoid capturing the aortic cusp into one of the patch sutures.
• Intraoperative transesophageal echocardiographic monitoring can be extremely helpful in precisely defining aortic valve prolapse and the severity of valve insufficiency, which determine the necessity of valvuloplasty. Follow-up intraoperative assessment should be used to rule out residual insufficiency.
• More extensive damage to the aortic valve from long-standing prolapse and distortion may require valve replacement.

Diet

No special dietary guidelines or restrictions are necessary.

Activity

Activity level is determined by the age at which signs or symptoms develop.

• Infants with large left-to-right shunts, particularly with complex left heart obstruction, may have delays in development of gross motor skills that naturally may restrict activity level.
• Patients with small left-to-right shunts without aortic valve insufficiency or with only trivial aortic valve insufficiency generally should be allowed full activity without restriction.
• Older patients with more significant aortic valve insufficiency should be restricted from competitive athletics and from sustained isometric types of activities (eg, weight lifting, rope pulls, sustained heavy lifting on the job).

MEDICATION

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For patients who develop aortic valve insufficiency, surgical closure of the VSD and repair of valve insufficiency is the preferred treatment. If surgical repair must be postponed, afterload reducers, such as angiotensin-converting enzyme (ACE) inhibitors or calcium channel blockers, have proved helpful in adults and children.

Drug Category: ACE inhibitors

Have proved beneficial in long-term therapy for aortic valve insufficiency. Positive effects include reduction in pulse pressure, reduction in regurgitant volume, reduction in left ventricular volume, and reduction in left ventricular mass (because of beneficial effects on ventricular remodeling).

Drug Category: Calcium channel blockers

Calcium channel blockers also have proved effective in reducing afterload and reducing pulse pressure and regurgitant volume. Prolonged regular use may stabilize left ventricular volume, but the effect on left ventricular muscle mass is less pronounced than that of ACE inhibitors.

FOLLOW-UP

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Complications

• Infective endocarditis
• • Patients with supracristal VSD are at increased risk of infective endocarditis.
  • The risk is relatively high if aortic valve insufficiency is present.
  • For more information, see Antibiotic Prophylactic Regimens for Endocarditis.
• Aortic insufficiency
• • 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 left-to-right shunt only.
  • Onset of aortic valve prolapse and progressive aortic insufficiency generally begins in children aged 6-10 years, although aortic insufficiency may develop even in infants.

Prognosis

• Prognosis should be considered good to excellent when the potential complication of aortic valve insufficiency is recognized and treated aggressively.
• Delayed recognition of or surgical treatment for progressive aortic valve insufficiency may lead to severe distortion of the aortic valve leaflet, making valve replacement more likely.

Patient Education

• The risk for infective endocarditis is higher for supracristal VSD with aortic insufficiency than for "simple" VSD alone. Patients and families should be educated not only about the importance of endocarditis prophylaxis, but also on the importance of good oral and dental hygiene.
• For excellent patient education resources, visit eMedicine's Heart Center. Also, see eMedicine's patient education article Ventricular Septal Defect.

MISCELLANEOUS

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Medical/Legal Pitfalls

• Failure to appreciate the unique natural history of supracristal VSD compared to other types of VSD
• • VSDs less likely to close spontaneously
  • VSDs more likely to be complicated by aortic insufficiency
• Delay in acting on aortic valve deformity and progressive aortic insufficiency with the goal of avoiding aortic valve replacement
• Failure to continue follow-up care after supracristal VSD repair and aortic valvuloplasty because aortic insufficiency may not be corrected completely
• Failure to diagnose supracristal VSD adequately before surgery because this type of VSD usually is not seen adequately from the standard right atrial surgical approach

Special Concerns

• Recurrence risk for offspring of mothers with supracristal VSD is estimated at 4-5%. Recurrence risk for fathers is approximately 2-3%. Detailed prenatal fetal ECHO may be indicated. Supracristal VSD cannot be identified from a routine prenatal 4-chamber view.

MULTIMEDIA

Section 10 of 11  

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Media file 1:  Parasternal long-axis echocardiogram view showing supracristal ventricular septal defect (arrow) with buckling and prolapse (***) of the right coronary leaflet of the aorta.
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Media file 2:  Parasternal short-axis echocardiogram view with color Doppler showing proximity of ventricular septal defect jet to the aortic and pulmonic valves. The patient is an infant who has not yet developed aortic valve prolapse or aortic insufficiency.
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Media type:  Photo

Media file 3:  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 who has not yet developed aortic valve prolapse and insufficiency.
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Media type:  Photo

Media file 4:  Transesophageal horizontal view of aortic root and right ventricle, showing sinus of Valsalva aneurysm leaking through a supracristal ventricular septal defect (VSD)(> <). Lack of supporting tissue in VSD may be one of the mechanisms involved in producing sinus of Valsalva aneurysms.
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Media type:  Photo

REFERENCES

Section 11 of 11

• Authors and Editors
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Article Last Updated: Apr 12, 2006