Congenital Heart Defect Definition: 

• • Abnormal heart formation during embryonic development in the uterus
  • Multiple causes (discussed later)

Physiological consequences:

• Defective heart → decreased function
  • ↓ Stroke volume
  • ↓ Cardiac output
  • Meets definition of congestive heart failure (CHF)
• Physiological consequences
  • ↓ Oxygenated blood delivery to tissues
  • Delayed growth and development
  • Poor weight gain
  • ↓ ATP production → impaired mitosis
  • Digestion requires energy → feeding intolerance

Signs and Symptoms:

• Feeding difficulties
  • Pulmonary edema makes breathing + nursing difficult
  • Poor feeding in infants and toddlers
• Respiratory manifestations
  • Orthopnea (worse breathing when lying flat)
  • Fluid pooling in lungs
  • Frequent waking due to dyspnea
  • Tripod position / squatting
    • Leaning forward improves breathing
  • Other signs:
    • Cough
    • Rapid respirations
    • Grunting
    • Nasal flaring
    • Wheezing

Diagnostic findings

• • Cardiomegaly
  • Arterial blood gases (ABGs) → assess hypoxia
  • Heart sounds
    • Murmurs / swooshing
    • Causes:
      • Valve stenosis
      • Valve regurgitation
  • Hemodynamic measures
    • Central venous pressure (CVP)
    • Pulmonary capillary wedge pressure (PCWP)
    • Assess left ventricular strength
• Clinical signs
  • Hypoxia
  • Cyanosis (blue discoloration)

Epidemiology – FYI:

• • 8 per 1,000 births in Canada
  • Occur early in embryogenesis (first 4 weeks)

Risk factors:

• • Alcohol exposure
  • Drug exposure
  • Viral infections
    • Rubella (German measles)
  • Sexually transmitted infections
    • Syphilis
  • Genetic conditions
    • Down syndrome
  • Maternal diabetes
  • Other developmental defects may occur:
    • Cleft palate

Categories of Congenital Heart Defects:

1. Ventricular and Atrial Septal Defects:

• Ventricular septal defect (VSD)
  • Hole in interventricular septum
  • Size and location vary
  • Causes left-to-right shunt
    • Left ventricle = higher pressure
  • Consequences:
    • Loss of oxygenated blood
    • ↓ Stroke volume
    • ↓ Cardiac output
    • Acyanotic (pink baby)
  • Risk:
    • Pulmonary hypertension → possible shunt reversal
• Atrial septal defect (ASD)
  • Hole between atria
  • Left-to-right shunt
  • Similar effects:
    • ↓ Stroke volume
    • Acyanotic

2.  Valvular Defects:

• Most commonly affected:
  • Aortic valve
  • Pulmonary valve
• Types:
  • Stenosis (narrowing)
  • Incompetence / regurgitation
• Consequences:
  • Heart hypertrophy
  • Heart failure
• Treatment:
  • Valve replacement
    • Mechanical valve
    • Bioprosthetic (pig) valve

Mitral and Aortic Valve Prolapse (floppy valve) Regurgitation Examples

1. Mitral Regurgitation (Mitral Insufficiency):

• Definition: The mitral valve leaks, causing blood to flow backward from the left ventricle into the left atrium during ventricular contraction (systole).
• Effects:
  • Volume overload in the left atrium.
  • Increased dilation and hypertrophy of the left ventricle as it compensates.
  • Reduced forward flow into the systemic circulation, leading to poor tissue and organ perfusion.
  • Possible pulmonary congestion due to backward flow into the pulmonary veins, resulting in pulmonary edema.

2. Aortic Regurgitation (Aortic Insufficiency):

• Definition: The aortic valve leaks, allowing blood to flow backward from the aorta into the left ventricle during ventricular relaxation (diastole).
• Effects:
  • Volume overload in the left ventricle.
  • Similar dilation and hypertrophy as the ventricle struggles to handle increased volume.
  • Decreased effective blood ejection into systemic circulation.
  • Blood backups into the pulmonary circulation, causing pulmonary edema.

Common Consequences:

• Both mitral and aortic valve prolapse conditions reduce blood supply to tissues and organs.
• The backward flow increases pressure in the pulmonary circulation.

These are potentially life-threatening, especially if untreated, leading to heart failure.

3.  Aortic Stenosis:

• • ↓ Stroke volume
  • ↑ Left ventricular workload
  • Pathologic hypertrophy
  • → Left-sided CHF

4.  Tetralogy of Fallot (cyanotic defect):

• Four abnormalities
  1. Pulmonary stenosis
  2. Right ventricular hypertrophy
  3. Ventricular septal defect
  4. Overriding (dextropositioned) aorta
• Pathophysiology:

• • Right-sided pressure > left
  • Right-to-left shunt
  • Deoxygenated blood enters systemic circulation

• Outcome:

• • Severe cyanosis
  • “Blue baby”
  • Requires surgical repair
  • Often heart transplant consideration

Acyanotic and Cyanotic Congenital Heart Defects:

• • Progress to congestive heart failure
  • Classified as:
    • Acyanotic (“pink baby”)
    • Cyanotic (“blue baby”) → more severe

Body’s Compensatory Responses

• • Activation of:
    • Sympathetic nervous system
    • Renin–angiotensin system
  • Results:
    • Tachycardia
    • Peripheral vasoconstriction
    • Pallor / cyanosis
    • Pulse deficit (apical > peripheral pulse)

Chronic Hypoxia – Signs and Symptoms:

• • Dyspnea
  • Squatting / tripod posture
  • Clubbing of fingers
  • Poor exercise tolerance
  • Poor tolerance to temperature extremes
  • Delayed growth and development
  • ↑ Erythropoietin → ↑ RBC production

Treatment:

• • Surgical repair
  • Some defects may self-correct

Summary:

• Congenital heart defects (CHDs) result from abnormal heart development early in embryogenesis (often within the first 4 weeks of pregnancy). They affect about 8 in 1,000 infants in Canada.
• Risk factors include alcohol and drug exposure, viral infections (e.g., rubella), STIs (syphilis), maternal diabetes, and genetic conditions (e.g., Down syndrome).
• CHDs often cause ↓ stroke volume and ↓ cardiac output, leading to congestive heart failure.
• Reduced cardiac output results in poor oxygen delivery, causing delayed growth, poor weight gain, feeding difficulties, and low energy for metabolism and development.
• Respiratory signs include pulmonary edema, dyspnea, orthopnea, rapid respirations, grunting, wheezing, nasal flaring, and use of tripod or squatting positions to ease breathing.
• Clinical findings may include cyanosis (blue baby) or acyanosis (pink baby), tachycardia, pulse deficits, clubbing of fingers, and poor exercise tolerance.
• Diagnosis involves detecting murmurs, cardiomegaly, hypoxia (ABGs), and abnormal cardiac pressures.
• Untreated defects can progress to heart failure; many require surgical repair, though some may self-resolve.
• Major defect categories:
  • Septal defects (ASD, VSD): Typically cause left-to-right shunts, reduced effective cardiac output, and are usually acyanotic.
  • Valvular defects: Most commonly aortic or pulmonary stenosis or regurgitation, leading to hypertrophy and heart failure.
  • Tetralogy of Fallot: A severe cyanotic defect with right-to-left shunting, resulting in significant hypoxia and requiring urgent surgical management.