What are congenital heart defects, including their assessment, pharmacology, and pathophysiology?

Congenital Heart Defects: Assessment, Pharmacology, and Pathophysiology

Congenital heart defects (CHDs) are structural abnormalities of the heart present at birth, affecting approximately 0.4-1% of live births, with varying complexity from simple lesions like isolated small atrial septal defects to complex conditions like single ventricle defects that significantly impact morbidity and mortality. 1

Definition and Classification

CHDs are classified according to anatomical complexity by the American College of Cardiology/American Heart Association as:

• Simple defects:

  • Isolated small atrial septal defect (ASD)
  • Isolated small ventricular septal defect (VSD)
  • Mild pulmonary stenosis

• Moderate complexity defects:

  • Larger ASDs and VSDs
  • Partial atrioventricular canal defects

• Complex defects:

  • Tetralogy of Fallot
  • Transposition of the great arteries
  • Functionally univentricular heart
  • Cyanotic heart defects 2, 1

Epidemiology

• Overall prevalence: 81.4 per 10,000 births
• Most common defects:
  • Muscular VSD (27.5 per 10,000)
  • Perimembranous VSD (10.6 per 10,000)
  • Secundum ASD (10.3 per 10,000)
  • Tetralogy of Fallot (4.7 per 10,000) 1

Pathophysiology

The pathophysiology of CHDs involves abnormal cardiac development during fetal life, resulting in structural abnormalities that affect:

1. Blood flow patterns: Abnormal shunting between chambers (left-to-right or right-to-left)
2. Oxygenation: Reduced or mixed oxygenation leading to cyanosis in some defects
3. Cardiac workload: Volume or pressure overload on specific chambers
4. Pulmonary circulation: Increased or decreased pulmonary blood flow 3, 4

Specific pathophysiological mechanisms include:

• Septal defects: Abnormal communications between cardiac chambers causing shunting
• Outflow tract obstructions: Stenosis or atresia affecting blood flow from ventricles
• Complex malformations: Combinations of defects affecting multiple aspects of cardiac function 2

Assessment

Clinical Evaluation

• Physical examination findings:
  • Heart murmurs (characteristic for specific defects)
  • Cyanosis (in right-to-left shunting lesions)
  • Growth failure
  • Exercise intolerance
  • Signs of heart failure 4

Diagnostic Imaging

• Echocardiography:

  • 2D echocardiography: Core imaging modality for CHD
  • 3D echocardiography: Provides incremental information for complex anatomy
  • Transthoracic and transesophageal approaches 2

• Other imaging modalities:

  • Electrocardiogram: May show chamber enlargement, conduction abnormalities
  • Chest X-ray: Cardiomegaly, abnormal pulmonary vasculature
  • Cardiac MRI: Detailed anatomic and functional assessment
  • Cardiac catheterization: Hemodynamic assessment and interventional procedures 4, 5

Fetal Diagnosis

• Antenatal anomaly screening and fetal echocardiography enable early detection
• Fetal electrocardiography can complement ultrasound for screening
• Markers such as prolonged pre-ejection period (>75 msec) and QTc intervals (>440 msec) may indicate hemodynamic alterations 6, 5

Pharmacological Management

Pharmacological treatment varies based on the specific defect and hemodynamic consequences:

1. Prostaglandin E1:

   • Critical for maintaining ductal patency in duct-dependent lesions
   • Used in neonates with critical CHDs before definitive intervention 6

2. Heart failure management:

   • Diuretics: Reduce fluid overload
   • ACE inhibitors: Afterload reduction
   • Beta-blockers: For ventricular dysfunction

3. Pulmonary hypertension therapy:

   • Endothelin receptor antagonists
   • Phosphodiesterase inhibitors
   • Prostacyclin analogs

4. Antiarrhythmics:

   • For associated rhythm disturbances
   • Particularly important in adults with CHD 7

Management Approaches

Management strategies depend on defect complexity:

• Simple defects: Monitoring or minimally invasive interventions
• Moderate to complex defects: Surgical repair or palliation
• Critical defects: Immediate stabilization followed by definitive repair 1

Long-term Outcomes

• For tetralogy of Fallot, long-term survival after complete repair is 86% at 32 years
• Risk of sudden cardiac death increases over time (6-9% by 30 years post-surgery)
• Adults with CHD require lifelong specialized care to monitor for late complications 1, 7

Special Considerations

• Transition from pediatric to adult care: Critical for continuity of management
• Pregnancy in women with CHD: Requires specialized multidisciplinary care
• Exercise recommendations: Individualized based on specific defect and repair status
• Prevention of endocarditis: Appropriate antibiotic prophylaxis for high-risk lesions

Common Pitfalls and Caveats

• Delayed diagnosis: Some defects may not present until adulthood
• Residual lesions: Post-surgical patients often have residual abnormalities requiring monitoring
• Arrhythmia risk: Increased risk of atrial and ventricular arrhythmias in repaired CHD
• Pulmonary hypertension: Can develop late after repair of left-to-right shunts
• Ventricular dysfunction: Progressive ventricular failure may occur decades after repair

The management of adults with CHD requires specialized care in centers with expertise in adult congenital heart disease to optimize outcomes and quality of life 7.