Congenital Heart Defects and Normal Heart

Congenital Heart Defects

• Definition: Congenital heart defects (CHD) are malformations of the heart or its associated blood vessels present at birth.
• Incidence: The number of children reaching adulthood with congenital heart disease has increased over the last 5 decades due to advances in diagnosis, medical, critical, and surgical care.

Normal Heart

• Fetal circulation: Four shunts in fetal circulation:
  • Placenta: Oxygen and nutrients from the mother's blood are transferred to the fetus.
  • Foramen ovale: Bypasses the lungs and moves blood from the right atrium to the left atrium.
  • Ductus arteriosus: Moves blood from the pulmonary artery to the aorta.
  • Ductus venosus: Passes highly oxygenated blood through the liver to the inferior vena cava and then to the right atrium of the heart.
• Fetal circulation: Oxygenated blood enters the fetus via the umbilical vein, bypasses the liver via the ductus venosus, mixes with deoxygenated blood, and is shunted from the right to left atrium via the foramen ovale.

Cardiopulmonary Changes at Birth

• Cessation of blood flow in the umbilical vein results in closure of the ductus venosus and becomes ligamentum venosum.
• Right atrial pressure falls, and closure of the foramen ovale occurs due to increased left atrial pressure.
• Ductus arteriosus closure occurs due to increased arterial oxygen saturation, which decreases prostaglandins circulation.

Cardiac Defects

• Types of cardiac defects:
  • Acyanotic heart diseases (68%): Occurs when blood flows from the left side of the heart to the right side of the heart due to a structural defect (hole) in the interventricular septum.
    • Ventricular septal defects (VSD)
    • Atrial septal defects (ASD)
    • Atrioventricular septal defects (AVSD)
    • Patent ductus arteriosus (PDA)
    • Pulmonary stenosis (PS)
    • Aortic stenosis (AS)
    • Coarctation of the aorta
  • Cyanotic heart diseases (22%): Occurs when a mixture of oxygenated and deoxygenated blood enters the systemic circulation.
    • Tetralogy of fallot (TOF)
    • Tricuspid atresia
    • Transposition of great vessels
    • Truncus arteriosus

Aetiology

• Genetic causes: Interaction of several genes, risk of recurrence if 1st-degree relative is affected.
• Chromosomal abnormalities: e.g., Downs syndrome associated with atrioventricular septal defect (AVSD) and Turner's syndrome associated with coarctation of the aorta.
• Environmental factors: e.g., Congenital rubella syndrome associated with patent ductus arteriosus (PDA), drugs like lithium associated with pulmonary or aortic stenosis.

Presenting Complaints/Signs

• Failure to thrive
• Exercise intolerance
• Easy fatigability
• Chest in-drawing
• Sweating during feeding
• Bluish spells/cyanosis
• Fever
• Convulsions

Specific Defects

• Ventricular septal defect (VSD): An abnormal opening in the ventricular septum, allowing free communication between the right and left ventricles.
• Atrial septal defect (ASD): An opening in the atrial septum, permitting free communication of blood between the atria.
• Atrioventricular septal defect (AVSD): Results from incomplete fusion of the endocardial cushions, which help to form the atrial septum, ventricular septum, and septal leaflets of the tricuspid and mitral valves.
• Patent ductus arteriosus (PDA): Occurs due to persistence of the ductus arteriosus, normally closing in the 1st week of life.
• Pulmonary stenosis (PS): A rare acyanotic congenital heart defect that involves a defect in the pulmonary valve.
• Aortic stenosis (AS): An obstruction to the outflow from the left ventricle at or near the aortic valve.
• Coarctation of the aorta: A narrowing of the aorta, resulting in severely reduced blood flow.
• Tetralogy of fallot (TOF): Involves four heart malformations, including pulmonary stenosis, overriding aorta, VSD, and right ventricular hypertrophy.
• Transposition of great vessels: Aorta arises from the right ventricle, and pulmonary arteries from the left ventricle.
• Truncus arteriosus: A rare defect in which a single common blood vessel comes out of the heart, instead of the usual two vessels.
• Tricuspid atresia: A birth defect of the heart where the valve that controls blood flow from the right upper chamber to the right lower chamber of the heart doesn't form at all.