DESCRIPTION

• Atrioventricular (AV) canal defects include a spectrum of anomalies caused by maldevelopment of the endocardial cushions.
• 3 major potential hemodynamic disturbances contribute to the pathophysiology, natural history, and medical and surgical management of these lesions.
• The relative effects of interatrial shunting, interventricular shunting, and AV valve function will determine the general course of patients with uncomplicated AV canal defects.
• The term complete atrioventricular canal defect refers to a heart with both significant ventricular and atrial components, whereas partial atrioventricular canal defect refers to a predominant primum atrial defect, cleft mitral valve, or restrictive or no ventricular shunting.
• Unbalanced canal defect refers to hearts with a right or left dominant ventricle.
• These are often associated with hypoplasia or atresia of 1 side of the common AV valve.

EPIDEMIOLOGY

• AV canal defects occur in 4–5% of patients diagnosed with congenital heart disease.
• Among patients with Down syndrome, 40–50% will have congenital heart disease, and, among those, ~40% will have AV canal defects.

Pregnancy Considerations

• Fetal diagnosis of AV canal defects is readily made on the 4-chamber view of the fetal heart alone.
• Identifying features include absence of primum atrial septum, loss of the offsetting of the mitral valve above the tricuspid valve at the crux of the heart, and an inlet ventricular septal defect.
• The relative size of the atrial and ventricular septal defects, the size of the LV and RV, and the degree of AV valve insufficiency, if any, should be specifically evaluated.
• Currently, no specific in utero management other than prenatal counseling is available for this diagnosis.

RISK FACTORS

Genetics

• Complex AV canal defects with hypoplasia of 1 ventricle and/or variable degrees of pulmonary stenosis are associated with heterotaxy syndromes.
• Families in which several members had AV canal defects not associated with trisomy 21 have been described.
• An abundance of candidate genes for nonsyndromic AV canal defects have been identified through animal models and biochemical studies, but determining which actually contribute to the pathogenesis of AVSD has been difficult.

COMMONLY ASSOCIATED CONDITIONS

Associated cardiac anomalies include straddling, stenosis, or atresia of part of the AV valve, often associated with hypoplasia of a ventricular chamber. Occasionally, complete AV canal defects are seen in combination with tetralogy of Fallot.

Outline

• Description
• Epidemiology
  • Pregnancy Considerations
• Risk Factors
  • Genetics
• Commonly Associated Conditions

Signs and symptoms:

• Patients with mainly atrial shunting are generally recognized following detection of a cardiac murmur on routine pediatric evaluation.
• The exam is similar to that noted in patients with isolated secundum atrial septal defects [systolic pulmonic flow murmur with fixed wide splitting of 2nd heart sound (S2)], often with the additional finding of an apical blowing systolic murmur of mitral regurgitation.
• A low-pitched diastolic rumble may be heard at the mitral area. Patients with complete AV canal defects are usually symptomatic by 4–6 wk of life.
• Those noted to have earlier signs of CHF in the 1st–2nd wk often have significant AV valve regurgitation.
• This occurs in up to 20% of patients. Failure-to-thrive, tachypnea, tachycardia, and poor feeding are common presenting symptoms.
• Physical exam also may reveal a pulmonary flow murmur, fixed splitting of the S2, a blowing systolic murmur of AV valve regurgitation, and often a mid-diastolic low-pitched rumble.
• When the ventricular septal defect is unrestrictive, it often does not generate a prominent separate systolic murmur.

DIAGNOSTIC TESTS & INTERPRETATION

Generally, cardiac catheterization is unnecessary in uncomplicated cases, unless pulmonary vascular disease or associated cardiac lesions such as tetralogy of Fallot are suspected.

Lab

The ECG usually shows a RV conduction delay pattern, and PR interval prolongation may be present. A left superior QRS axis is almost always noted.

Imaging

• The diagnosis of all variants is readily confirmed on 2D echo.
• 3D echo and MRI have been shown to be beneficial in the planning of residual AV-valve disease repair.
• Occasionally, a dilated coronary sinus secondary to a left superior vena cava can be identified incorrectly as a primum atrial septal defect.
• Careful visualization of the intact primum septum (anterior to the coronary sinus) and tracing of the course of the left superior vena caval connection help differentiate this possibility.
• Color flow Doppler is helpful in estimating the degree of mitral regurgitation.
• Searching for evidence of increased RV pressure (ventricular hypertrophy, septal orientation, and Doppler estimation of pressure on the basis of tricuspid regurgitation) is important in the echo assessment of these defects.
• In complete AV canal defects, attention should be directed to the morphology and attachments of the AV valve leaflets and estimating the sizes of RV and LV.
• These observations are important in determining the type of surgical management.

DIFFERENTIAL DIAGNOSIS

• Patients with mainly atrial shunting may present similarly to patients with isolated secundum atrial septal defects.
• If a restrictive ventricular septal defect is present, a left sternal border pansystolic murmur may be dominant, suggesting an isolated ventricular septal defect.
• Complete AV canal defects may present similarly to moderate to large ventricular septal defects.

Outline

• Information
• Diagnostic Tests & Interpretation
  • Lab
  • Imaging
• Differential Diagnosis

Early management involves close observation until signs of CHF appear, when anticoagulant therapy will most likely be necessary to control symptoms.

ADDITIONAL TREATMENT

General Measures

• Medical intervention in the form of inotropes, afterload reduction, or diuretics are usually not indicated in the group of asymptomatic patients with partial AV canal defects.
• Endocarditis prophylaxis is required in the presence of AV valve regurgitation.
• Most patients with complete AV canal defects require inotropic and diuretic therapy in the 1st weeks–months of life to control symptoms of CHF and improve feeding intake and weight gain.
• Often it is difficult to determine the primary cause of poor feeding in the setting of patients with Down syndrome who may be feeding poorly because of noncardiac issues despite optimal medical management.

SURGERY

• Surgical repair in partial AV canal patients is indicated when a clear cut defect is identified and clinical or echo evidence of cardiac chamber dilation.
• The timing of repair is elective and similar to that for closure of isolated secundum atrial septal defects.
• The majority of defects should be closed by 2–5 yr of age.
• Patients with trivial defects can be followed medically.
• Surgical repair in complete AV canal patients is indicated in the setting of severe symptoms resistant to medical therapy or failure to thrive.
• Patients whose conditions are well controlled with adequate weight gain on medical therapy nevertheless should undergo complete repair prior to 4–5 mo of age to avoid irreversible pulmonary vascular disease.
• Relatively early repair is particularly important in the large subgroup of patients with Down syndrome.
• This group has been shown to have a greater degree of elevation of pulmonary vascular resistance in the 1st yr of life and may have more rapid progression to fixed pulmonary obstructive disease than children with normal chromosomes.

Outline

• Additional Treatment
  • General Measures
• Surgery

FOLLOW-UP RECOMMENDATIONS

Patient Monitoring

Close regular visits for assessment of adequacy of weight gain and or signs of CHF

PROGNOSIS

• Results of surgical repair of primum atrial septal defects and partial AV canal defects have been excellent, with a mortality rate of <1% and a reoperation rate of <3%.
• Late death after surgery is rare, reported in 0–4% of patients.
• The overall long-term survival of patients with primum atrial septal defect following repair was found to match that of the general population.
• Residual interatrial communication rarely occurs.
• Left AV valve regurgitation is the major cause of late morbidity in all forms of AV canal defects.
• In partial canal repair follow-up studies, the incidence of significant regurgitation requiring reoperation ranges from 7–10% of patients.
• Subaortic stenosis is noted in <5% of postoperative patients.
• The early postoperative mortality rate following repair of complete AV canal defects has been reduced from ~20–25% in the past to 3–4% in the current era.
• Strong risk factors for early death included postoperative pulmonary hypertensive crisis, immediate postoperative severe left AV regurgitation, and double-orifice left AV valve.
• Improved surgical skills, postoperative care of small infants, and management of perioperative pulmonary HTN are undoubtedly responsible for the notable decline in early mortality. Despite the decrease in postoperative mortality and decrease in the incidence of pulmonary vascular disease, reoperation due to severe mitral valve dysfunction remains the primary contributor to reoperation.
• Intraoperative transesophageal echo has been noted to favorably alter surgical treatment in some patients by detecting inadequate repair in the operating room.
• Heart block, residual ventricular septal defect, LV outflow tract obstruction, and mitral valve dysfunction are potential long-term complications that must be considered in patients following repair of complete AV canal defects.
• Persistent elevation of pulmonary vascular resistance may be an issue in some patients, especially if surgical correction was delayed, or pulmonary vascular resistance was marginal at the time of surgery.
• Reoperation for residual mitral regurgitation recently has been reported at rates varying from 2–10%.

Outline

• Follow-Up Recommendations
  • Patient Monitoring
• Prognosis

CODES

ICD9

• 745.60 Endocardial cushion defect, unspecified type
• 745.61 Ostium primum defect
• 745.69 Other endocardial cushion defects

SNOMED

• 15459006 endocardial cushion defect (disorder)
• 17718000 ostium primum defect (disorder)
• 253374008 congenital abnormality of atrioventricular valves and atrioventricular septal defect (disorder)

ADDITIONAL READING

• Barrera C, Levasseur S, Roman K, et al. Three-dimensional echocardiography improves the understanding of left atrioventricular valve morphology and function in atrioventricular septal defects undergoing patch augmentation. J Thorac Cardiovasc Surg. 2005;129(4):746–753.
• Castaneda AR, Jonas RA, Mayer JE, et al. Atrioventricular canal defects. In: Cardiac Surgery of the Neonate and Infant. Philadelphia: WB Saunders; 1994;167–186.
• Kirklin JW, Barrat-Boyes BG. Atrioventricular canal defect. In: Cardiac Surgery. New York: Churchill Livingstone, 1993;693–749.
• Laks H, Pearl JM. Primum atrial septal defect. Semin Thorac Cardiovasc Surg. 1997;9:2–7.
• Maslen CL. Molecular genetics of atrioventricular septal defects. Curr Opin Cardiol. 2004;19(3):205–210.
• Suzuki T, Bove EL, Devaney EJ, et al. Results of definitive repair of complete atrioventricular septal defect in neonates and infants. Ann Thorac Surg. 2008;86(2):596–602.
• Ten Harkel AD, Cromme-Dijkhuis AH, Heinerman BC, et al. Development of left atrioventricular valve regurgitation after correction of atrioventricular septal defect. Ann Thorac Surg. 2005;79(2):607–612.

Howard D. Apfel

Welton M. Gersony