Congenital Heart Disease: Development and Classification

Introduction

• Congenital heart disease (CHD) is a defect in the heart present at birth and the most common form of birth defects.
• Leading cause of death from birth abnormalities in the first year of life.
• Affects approximately 8 out of 10,000 live births.
• Treatment advancements include medications, catheter-based interventions, and surgery.

Heart Embryology and Development

• Primitive heart begins to beat around day 22-23 of embryo growth.

• Heart looping: series of constrictions and dilations forming primitive heart chambers.

• Septation: Occurs between the 4th-6th week.

  • Atrial Septation:
    • Septum primum grows from the dorsal wall of atrium.
    • Osteum primum decreases as septum primum grows, eventually fusing with endocardial cushions.
    • Osteum secundum forms by merging small perforations in the septum.
    • Septum secundum grows over septum primum, creating foramen ovale.
  • Ventricular Septation:
    • Begins at end of 4th week with interventricular foramen.
    • By 7th week, forms membranous portion of interventricular septum.

• Valve Development:

  • Aortic and Pulmonary Valves: Form around 5 weeks.
  • Atrioventricular Valves: Formed from tissue surrounding AV canals.

• Fetal Circulation and Shunts:

  • Bypass lungs and liver.
  • Ductus Venosus: Bypasses liver, joins inferior vena cava.
  • Foramen Ovale: Shunts blood from right to left atrium.
  • Ductus Arteriosus: Directs blood from pulmonary artery to aortic arch.
  • Shunts close after birth, allowing normal lung function.

Classification of Congenital Heart Defects

• Acyanotic Lesions:

  • Shunt of blood from left to right atrium.
  • Include intercardiac or vascular stenosis or regurgitation.

• Cyanotic Lesions:

  • Recognized by blue/purple skin discoloration.
  • Caused by desaturation of blood; infants with these lesions often called "blue babies".
  • Include diminished pulmonary blood flow or increased pulmonary resistance.

Classification Approaches

1. Physiologic:

   • Left to right shunt lesions without cyanosis.
   • Acyanotic outflow obstructive lesions.

2. Cyanotic Lesions:

   • Decreased pulmonary blood flow lesions with cyanosis.
   • Increased pulmonary blood flow lesions with cyanosis.
   • Increased pulmonary vascular resistance lesions.

3. Genetic Disorders Associated with CHD:

   • Trisomy 13, 18, 21: Atrial and ventricular septal defects, patent ductus arteriosus.
   • Turner Syndrome: Left-sided obstructive lesions.
   • Williams Syndrome: Aortic stenosis and pulmonary artery obstruction.
   • Holt-Oram Syndrome: Atrial septal defects, ventricular septal defects.
   • Marfan Syndrome: Connective tissue issues, possible aortic aneurysm.

Inflammatory Disease

• Kawasaki Disease: Rare childhood illness affecting coronary arteries, can lead to aneurysm.

Conclusion

• Congenital heart disease classifications help in understanding and treatment planning.
• Genetic factors often play a role in the presence of congenital defects.