How are congenital heart defects classified?

Congenital Heart Defect Classifications

Congenital heart defects are classified according to the American Heart Association/American College of Cardiology (AHA/ACC) system into three anatomical complexity categories (simple, moderate, and great complexity), with an additional physiological staging system that considers functional status and sequelae. 1

Anatomical Classification

I. Simple Defects

• Isolated small defects:
  • Small atrial septal defect (ASD)
  • Small ventricular septal defect (VSD)
  • Mild isolated pulmonic stenosis
• Repaired conditions without significant residua:
  • Previously ligated or occluded ductus arteriosus
  • Repaired secundum ASD or sinus venosus defect without significant residual shunt
  • Repaired VSD without significant residual shunt or chamber enlargement

II. Moderate Complexity

• Anomalous connections:
  • Anomalous pulmonary venous connection (partial or total)
  • Anomalous coronary artery arising from pulmonary artery
  • Anomalous aortic origin of coronary artery from opposite sinus
• Septal defects:
  • Atrioventricular septal defect (AVSD)
  • Ostium primum ASD
  • Sinus venosus defect
  • Moderate/large unrepaired secundum ASD
  • VSD with associated abnormality and/or moderate or greater shunt
• Outflow tract abnormalities:
  • Infundibular right ventricular outflow obstruction
  • Congenital aortic valve disease
  • Congenital mitral valve disease
  • Subvalvar/supravalvar aortic stenosis
• Other:
  • Coarctation of the aorta
  • Ebstein anomaly
  • Pulmonary valve regurgitation (moderate or greater)
  • Pulmonary valve stenosis (moderate or greater)
  • Sinus of Valsalva fistula/aneurysm
  • Repaired tetralogy of Fallot
  • Straddling atrioventricular valve

III. Great Complexity (Complex)

• Cyanotic conditions:
  • Cyanotic congenital heart defect (unrepaired or palliated, all forms)
  • Pulmonary atresia (all forms)
  • Transposition of the great arteries (classic or d-TGA; congenitally corrected or l-TGA)
• Single ventricle physiology:
  • Single ventricle (including double inlet left ventricle, tricuspid atresia, hypoplastic left heart)
  • Fontan procedure
• Other complex lesions:
  • Double-outlet ventricle
  • Interrupted aortic arch
  • Mitral atresia
  • Truncus arteriosus
  • Other abnormalities of atrioventricular and ventriculoarterial connection 1

Physiological Staging System

The AHA/ACC guidelines incorporate a physiological staging system that complements the anatomical classification. This system categorizes patients based on functional status and sequelae:

Stage A

• NYHA Functional Class I symptoms
• No hemodynamic or anatomic sequelae
• No arrhythmias
• Normal exercise capacity
• Normal renal/hepatic/pulmonary function

Stage B

• NYHA Functional Class II symptoms
• Mild hemodynamic sequelae (mild aortic enlargement, mild ventricular enlargement, mild ventricular dysfunction)
• Mild valvular disease
• Trivial or small shunt (not hemodynamically significant)
• Arrhythmia not requiring treatment
• Abnormal objective cardiac limitation to exercise

Stage C

• NYHA Functional Class III symptoms
• Significant (moderate or greater) valvular disease
• Moderate or greater ventricular dysfunction
• Moderate aortic enlargement
• Venous or arterial stenosis
• Mild or moderate hypoxemia/cyanosis
• Hemodynamically significant shunt
• Arrhythmias controlled with treatment
• Pulmonary hypertension (less than severe)
• End-organ dysfunction responsive to therapy

Stage D

• NYHA Functional Class IV symptoms
• Severe aortic enlargement
• Arrhythmias refractory to treatment
• Severe hypoxemia (almost always associated with cyanosis)
• Severe pulmonary hypertension
• Eisenmenger syndrome
• Refractory end-organ dysfunction 1

Clinical Application of the Classification

The combined anatomical and physiological classification (ACHD AP Classification) guides:

1. Follow-up frequency:

   • Simple CHD: Every 2-3 years
   • Moderate complexity: Annual evaluation
   • Complex CHD: Every 6-12 months 2

2. Care setting requirements:

   • Complex CHD patients have better outcomes when managed in specialized ACHD centers with multidisciplinary teams 1
   • Patients with higher physiological stages require more intensive monitoring and intervention

3. Resource allocation:

   • Specialized imaging (echocardiography, CMR/CCT)
   • Electrophysiology services
   • Interventional cardiology
   • Cardiac anesthesiology with CHD expertise 1

Alternative Classification Approaches

Some alternative classification systems exist, including pathophysiological approaches that categorize CHD based on:

1. CHD with increased pulmonary blood flow (septal defects without pulmonary obstruction)
2. CHD with decreased pulmonary flow (septal defects with pulmonary obstruction)
3. CHD with obstruction to blood progression and no septal defects
4. CHD incompatible with postnatal blood circulation
5. CHD silent until adult age 3

However, the AHA/ACC anatomical and physiological classification remains the most widely accepted and clinically useful system in North America.

Important Considerations

• The classification system should guide clinical decision-making but must be applied with consideration of individual patient factors
• Regular reassessment is necessary as physiological stage can change over time
• Patients with complex CHD require lifelong specialized care to monitor for late complications 2
• Long-term survival varies significantly by defect type and repair status (e.g., 86% 32-year survival after tetralogy of Fallot repair) 2