Endocardial cushion defects, more commonly known as atrioventricular (AV) canal or septal defects, include a range of defects characterized by involvement of the atrial septum, the ventricular septum, and one or both of the AV valves.

Endocardial cushion defect is a congenital defect present at birth. The severity of the symptom complex and presentation is dependent directly upon the severity of the defect and the presence of mitral insufficiency.

These defects can be classified by several methods. A distinction generally is made between partial and complete defects. A complete AV septal defect indicates the presence of both atrial and ventricular septal defects with a common AV valve. A partial defect indicates atrial septal involvement with separate mitral and tricuspid valve orifices.

AV canal defects arise from abnormal development of the endocardial cushions. In these patients, the superior and inferior cushions do not close completely. An interatrial communication is left at the lower portion of the atrial septum. This is called an ostium primum defect. The failure of the endocardial cushions to fuse results in an abnormally low position of the AV valves and an abnormally high position of the aortic valve. A portion of the AV valves originates from the endocardial cushions, and their improper fusion results in anterior and posterior components to the mitral valve leaflet.

Pathophysiology

Predominant left-to-right shunting of blood through the heart occurs in these patients. In patients with partial defects, this occurs through the ostium primum atrial septal defect. When a complete endocardial cushion defect is present, a large ventricular septal defect as well as valvular insufficiency may develop, resulting in volume overload of both the left and right ventricles associated with heart failure in early life. In patients with long-standing pulmonary overload, pulmonary vascular disease may develop and congestive heart failure (CHF) symptoms may improve. This improvement is a poor prognostic indicator because it heralds the development of right-to-left shunting and irreversible pulmonary hypertension (ie, Eisenmenger syndrome).

Epidemiology

The frequency rate is about 3% of children who have congenital heart disease. Sixty to Seventy percent of these defects are of the complete form. More than half of those affected with the complete form have Down Syndrome.

Patients with only ostium primum atrial septal defect and minimal insufficiency of the left AV valve (ie, mitral valve) do well without treatment during infancy, childhood, and adolescence. During adulthood, these patients develop symptoms of CHF and atrial arrhythmia.Patients with septal defects and mitral valve insufficiency develop CHF early in life, with high rates of morbidity and mortality if the valvular insufficiency is pronounced. Patients with a complete defect develop CHF in infancy, with frequent respiratory infections and poor weight gain.

An infant may be relatively asymptomatic. In severe cases, patients have a history of poor feeding, chronic upper respiratory tract infections, pneumonia, and poor growth. The mother may notice difficulty with crying, frequent pauses during feeding, and nasal flaring. As the child grows older, the more common manifestations of CHF may develop, including aversion to activity and play, easy fatigability, dyspnea, and edema.

Physical

  • Partial defects present with the physical findings common to atrial septal defects.

    • The second heart sound is widely split without respiratory variations.
    • A systolic ejection murmur may be heart at the upper left sternal border.
    • A low-pitched early diastolic rumble may be heart at the lower left sternal border and is related to increased tricuspid valve flow.
    • A murmur of mitral insufficiency may or may not be present.
  • Additional findings in complete endocardial cushion defects relate to the ventricular septal defect and valvular insufficiency.
    • Poor physical development, hyperinflated thorax, bulging precordium, Harrison grooves, mild or intermittent cyanosis, and stigmata of Down syndrome (eg, oblique palpebral fissures, large protuberant tongue, short and broad hands, simian crease, inner epicanthic skin fold)
    • Arterial and jugular venous pulse – Water hammer pulse, dominant v wave in the jugular venous pulse
    • Precordial movement and palpation – Systolic thrill, palpable impulse in the second and third intercostal space representing a dilated pulmonary artery, prominent heave at the left sternal border
    • Auscultation
        • A single first heart sound is heard, which may be a relatively soft fixed splitting of the second heart sound.
        • A systolic murmur of a ventricular septal defect can be heard as well as the systolic murmur of mitral insufficiency.
        • Pulmonary hypertension is associated with a loud pulmonic component of the second heart sound.

      Genetics

      • The characteristic pattern of the malformation has been attributed to trisomy 21 and Down syndrome in some cases. Some evidence exists that a critical region of chromosome band 21q22 may contribute particularly to the cardiac malformation in this syndrome.
      • Other chromosomal abnormalities also can result in AV septal defects, in particular, deletion of 8p, partial 10q monosomy, partial 13q monosomy, ring 22 14 q+, and 1p+3p-.
      • In most cases of significant chromosomal aberration, AV septal defects are associated with other noncardiac congenital defects. However, isolated AV septal defects can be transmitted in families as an autosomal dominant trait.
      • Linkage analyses have suggested a locus for autosomal dominant AV septal defects on chromosome 1p but no specific gene defect has yet been identified.
      Growth factor aberrations: In the developing fetus, cardiac tissue formation is dependent upon appropriate growth factor stimulation including transforming growth factor beta and platelet-derived growth factor. Alterations in the concentration or efficacy of these factors during embryogenesis can contribute to the cardiac malformations.

    Treatment

    Medical treatment is designed to relieve the symptoms of CHF until operative correction is feasible. The objective of therapy is to avoid development of pulmonary vascular obstructive disease. When heart failure and associated pulmonary congestion are present, diuretics and digoxin are indicated.

      • Infants with partial AV septal defects that are symptomatic are referred for corrective surgery, which includes mitral valvuloplasty and closure of the atrial septal defect. Asymptomatic patients with an ostium primum defect are referred for elective repair after infancy.
      • Patients with complete AV septal defects who do not have associated right ventricular outflow obstruction generally have pulmonary artery pressures near systemic levels. These patients will develop pulmonary vascular disease after the first year of life and usually are referred for corrective surgery in infancy.
      • Historically, children were treated with pulmonary artery banding in infancy to protect the pulmonary vasculature from excessive blood flow and development of pulmonary vascular disease. Patients were referred for corrective surgery when older than 3-4 years.
      • Corrective surgery can be performed even in early infancy, in several ways. A single Dacron patch can be used to close the atrial and ventricular septal defect (see image below). The right and left portions of the common AV valve are then resuspended from the patch. A 2-patch technique also may be used.
      • Severe and irreversible pulmonary vascular disease is a contraindication to corrective surgery, and these children may be referred for cardiopulmonary transplantation.

     

    Source: Medscape