Endocardial Cushion Defect

Introduction to Endocardial Cushion Defect

Endocardial cushion defect, also known as atrioventricular septal defect (AVSD) or atrioventricular canal defect, is a congenital heart malformation involving the central fibrous body of the heart. It encompasses a spectrum of anomalies affecting the atrial septum, ventricular septum, and atrioventricular valves.

Key points:

  • Accounts for about 4-5% of all congenital heart defects
  • Strong association with Down syndrome (trisomy 21)
  • Can be classified into partial, transitional, and complete forms
  • Results in varying degrees of intracardiac shunting and valve regurgitation

Embryology

Normal Development

  1. Endocardial Cushions: Form at 4-5 weeks of gestation
  2. Fusion: Superior and inferior cushions fuse at 5-6 weeks
  3. Septation: Contributes to atrial septum, ventricular septum, and AV valves

Pathogenesis

  • Failure of Fusion: Primary defect in endocardial cushion development
  • Genetic Factors:
    • Down syndrome (40-50% of AVSD cases)
    • Other chromosomal abnormalities (e.g., trisomy 13, 18)
    • Single gene disorders (e.g., CRELD1 mutations)
  • Environmental Factors: Maternal diabetes, alcohol exposure

Types of Defects

  1. Partial AVSD:
    • Ostium primum atrial septal defect
    • Cleft mitral valve
  2. Transitional AVSD:
    • Ostium primum ASD
    • Cleft mitral valve
    • Small inlet VSD (restrictive)
  3. Complete AVSD:
    • Large defect involving both atrial and ventricular septum
    • Common AV valve

Clinical Presentation

Symptoms

  • Partial AVSD:
    • Often asymptomatic in infancy
    • Exercise intolerance in older children/adults
  • Complete AVSD:
    • Failure to thrive
    • Tachypnea, dyspnea
    • Recurrent respiratory infections
    • Congestive heart failure (2-3 months of age)

Physical Examination

  • General: Dysmorphic features (if associated with Down syndrome)
  • Cardiovascular:
    • Hyperactive precordium
    • Wide, fixed splitting of S2
    • Systolic murmur at left sternal border (VSD component)
    • Mid-diastolic rumble at apex (increased flow across AV valves)
  • Respiratory: Tachypnea, retractions (in heart failure)

Complications

  1. Pulmonary Hypertension: Due to increased pulmonary blood flow
  2. Eisenmenger Syndrome: In untreated cases with severe pulmonary hypertension
  3. Arrhythmias: Atrial fibrillation, flutter in adults with unrepaired defects
  4. Endocarditis: Risk increases with age in unrepaired defects

Diagnosis

Imaging Studies

  1. Echocardiography:
    • Primary diagnostic tool
    • Assesses defect size, valve morphology, and function
    • Evaluates chamber sizes and pulmonary pressures
  2. Chest X-ray:
    • Cardiomegaly
    • Increased pulmonary vascular markings
  3. Cardiac MRI:
    • Complementary to echocardiography
    • Useful for complex anatomy or in older patients
  4. Cardiac Catheterization:
    • Rarely needed for diagnosis
    • May be used to assess pulmonary vascular resistance

Electrocardiogram (ECG)

  • Left axis deviation
  • Right ventricular hypertrophy
  • Prolonged PR interval (characteristic of partial AVSD)

Prenatal Diagnosis

  • Fetal echocardiography can detect AVSD as early as 14-16 weeks gestation
  • Indication for fetal karyotyping due to association with chromosomal abnormalities

Management

Medical Management

  • Heart Failure Treatment:
    • Diuretics (e.g., furosemide)
    • ACE inhibitors (in select cases)
    • Digoxin (controversial, less commonly used)
  • Nutritional Support: High-calorie formulas, nasogastric feeding if necessary
  • Infection Prevention: RSV prophylaxis, routine immunizations

Surgical Management

  1. Timing:
    • Partial AVSD: 2-4 years of age (if asymptomatic)
    • Complete AVSD: 3-6 months of age
  2. Surgical Techniques:
    • Single or double-patch technique for septal defect closure
    • AV valve repair or replacement
  3. Outcomes:
    • Mortality: <5% in most centers
    • Reoperation rate: 10-15% (mainly for left AV valve regurgitation)

Long-term Follow-up

  • Regular cardiology follow-up with echocardiography
  • Monitoring for residual defects, valve function, and arrhythmias
  • Endocarditis prophylaxis as per current guidelines
  • Counseling regarding exercise, pregnancy, and career choices


Objective QnA: Endocardial Cushion Defect
  1. What is another name for endocardial cushion defect?
    Atrioventricular septal defect (AVSD)
  2. Which embryonic structure fails to develop properly in endocardial cushion defects?
    The endocardial cushions
  3. What is the most common chromosomal abnormality associated with endocardial cushion defects?
    Trisomy 21 (Down syndrome)
  4. Which part of the cardiac cycle is most affected by an endocardial cushion defect?
    Diastole
  5. What is the characteristic finding on an ECG in patients with complete AVSD?
    Superior QRS axis (between -30° and -150°)
  6. Which heart valve(s) are typically affected in endocardial cushion defects?
    Mitral and tricuspid valves
  7. What is the most common type of endocardial cushion defect?
    Complete AVSD
  8. In a complete AVSD, what structure is typically absent?
    The atrioventricular septum
  9. What is the term for the single atrioventricular valve seen in complete AVSD?
    Common atrioventricular valve
  10. Which cardiac chamber typically experiences volume overload in AVSD?
    The right ventricle
  11. What is the most common presenting symptom of AVSD in infants?
    Congestive heart failure
  12. At what age do symptoms typically appear in infants with complete AVSD?
    4-6 weeks of age
  13. What is the primary goal of surgical repair for AVSD?
    To separate the common AV valve into two separate valves and close the septal defects
  14. What is the optimal age range for elective surgical repair of complete AVSD?
    3-6 months of age
  15. Which complication is more common in AVSD repair compared to other congenital heart surgeries?
    Heart block
  16. What is the most common residual lesion after AVSD repair?
    Left atrioventricular valve regurgitation
  17. How does pulmonary vascular resistance typically change in untreated AVSD over time?
    It increases, potentially leading to Eisenmenger syndrome
  18. What is the characteristic murmur heard in patients with AVSD?
    Systolic ejection murmur at the left upper sternal border
  19. Which imaging modality is considered the gold standard for diagnosing AVSD?
    Echocardiography
  20. What is the term for the incomplete form of AVSD with only an atrial component?
    Ostium primum atrial septal defect
  21. In partial AVSD, which part of the mitral valve is typically cleft?
    The anterior leaflet
  22. What is the typical appearance of the AV valve in AVSD when viewed from the ventricular apex?
    A "goose-neck" deformity
  23. Which chamber demonstrates the most significant enlargement on chest X-ray in AVSD?
    The right atrium
  24. What is the risk of developing pulmonary vascular obstructive disease by 1 year of age in untreated complete AVSD?
    Approximately 50%
  25. Which medication is commonly used to manage symptoms of heart failure in infants with AVSD before surgery?
    Furosemide (Lasix)
  26. What is the typical location of the AV node in complete AVSD?
    Posterior and inferior to the coronary sinus ostium
  27. What is the term for the fibrous tissue between the superior and inferior bridging leaflets in AVSD?
    Scooping
  28. Which type of AVSD is more commonly associated with tetralogy of Fallot?
    Complete AVSD
  29. What is the long-term survival rate for patients with surgically repaired complete AVSD?
    Approximately 90% at 10 years
  30. Which genetic syndrome, other than Down syndrome, is associated with an increased risk of AVSD?
    Ellis-van Creveld syndrome


Further Reading
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