The 2025 Adult Congenital Heart Disease (ACHD) Anatomic and Physiological Classification System

The ACHD anatomic and physiological (AP) classification system was introduced in 2018 to more uniformly characterize ACHD anatomy and physiology. It aims to improve classification of disease severity given the potential for discordance between anatomic complexity and physiological stage. In addition, the AP classification system underpins the guidelines’ follow-up and procedural monitoring recommendations and has been shown to correlate with patient outcomes.

ACHD AP Classification
(CHD Anatomy + Physiological Stage = ACHD AP Classification)

CONGENITAL HEART DISEASE ANATOMY
CONGENITAL HEART DISEASE ANATOMY
I. Simple II. Moderate Complexity III. Great Complexity (or Complex)
Ostium secundum ASD Anomalous aortic origin of a coronary artery from the opposite sinus Double-outlet ventricle
Patent ductus arteriosus Anomalous coronary artery arising from the pulmonary artery Fontan physiology
Ventricular septal defect Anomalous pulmonary venous connection, partial or total Interrupted aortic arch
Pulmonic stenosis Atrioventricular septal defect (partial or complete) Pulmonary atresia (all forms, including tetralogy of Fallot with pulmonary atresia)
  Congenital aortic valve disease Single-ventricle anatomy (including double-inlet left ventricle, tricuspid/mitral atresia, hypoplastic left heart, or other functionally single ventricle)
  Congenital mitral valve disease Congenitally corrected TGA (CCTGA, levo-TGA)
  Coarctation of the aorta Dextro-TGA after atrial switch (Mustard/Senning) operation
  Cor triatriatum sinister Dextro-TGA after Rastelli operation
  Dextro-TGA after arterial switch operation Truncus arteriosus
  Ebstein anomaly Unrepaired or partially palliated cyanotic congenital heart defect
  Infundibular right ventricular outflow obstruction/double-chamber right ventricle  
  Peripheral pulmonary artery stenosis  
  Sinus venosus defect  
  Subvalvular aortic stenosis (excluding hypertrophic cardiomyopathy)  
  Supravalvar aortic stenosis  
  Tetralogy of Fallot  
  Vascular ring or sling  
PHYSIOLOGICAL STAGE
PHYSIOLOGICAL STAGE
Stage A Stage B Stage C Stage D
No cardiac symptoms Arrhythmia* not requiring new treatment or a change in therapy in the past 12 months BNP or NT-proBNP level ≥2 times the upper limit of normal Hospitalization for heart failure in the past 12 months
No hemodynamic or anatomic sequelae Mild native valve dysfunction* or prosthetic valve with normal function Hemodynamically significant shunt* Endocarditis in the prior 1 year
No sustained arrhythmias* Mild ventricular dysfunction Mild or moderate chronic hypoxemia* (baseline resting oxygen saturation 86%–92%) Eisenmenger syndrome
Normal exercise capacity* Mild ventricular enlargement Moderate or greater valvular dysfunction* NYHA functional class* III or IV symptoms
Normal pulmonary pressure Presence of a permanent pacemaker or ICD, without need for ICD therapy in the past 12 months Moderate or severe ventricular dysfunction (systemic, pulmonic, or both) Recurrent arrhythmias* that are hemodynamically significant and/or refractory to treatment
  Trivial or small shunt* (not hemodynamically significant) Pulmonary arterial hypertension (low-risk)* Severe hypoxemia* (baseline oxygen saturation ≤85%)
    Sustained or high-burden tachyarrhythmia in the past 12 months requiring treatment with antiarrhythmic drugs, ablation, cardioversion, or ICD therapy Pulmonary arterial hypertension* (intermediate- or high-risk)
TABLE 5: Physiological Variables as Used in ACHD AP Classification
TABLE 5: Physiological Variables as Used in ACHD AP Classification
Variable Description
Arrhythmia

Arrhythmias are very common in patients with ACHD and may be both the cause and the consequence of deteriorating hemodynamics, valvular dysfunction, or ventricular dysfunction. Given that arrhythmias are associated with symptoms, outcomes, and prognosis, they are categorized based on their presence and their response to treatment.

  • No sustained arrhythmia: No documented clinically relevant atrial or ventricular tachyarrhythmias.
  • Arrhythmia not requiring new treatment or a change in therapy in the past 12 months: Bradyarrhythmia, atrial or ventricular tachyarrhythmia not requiring new antiarrhythmic therapy, cardioversion, ablation, or pacemaker/ICD placement.
  • Recurrent arrhythmias that are hemodynamically significant and/or refractory to treatment.
Concomitant valvular heart disease (VHD)

Severity defined according to the 2020 VHD guideline:

  • Mild VHD
  • Moderate VHD
  • Severe VHD
Exercise capacity

Patients with ACHD are often asymptomatic despite exercise limitations that manifest as diminished exercise capacity upon objective evaluation; accordingly, assessing both subjective and objective exercise capacity is important (see NYHA classification system below). Exercise capacity is associated with prognosis.

  • Abnormal objective cardiac limitation to exercise is defined as an exercise maximum ventilatory equivalent of oxygen below the range expected for the specific congenital heart disease anatomic diagnosis.
Hypoxemia/hypoxia/cyanosis

See Section 3.5 of the 2025 ACHD Guideline for a detailed definition of cyanosis.

  • Hypoxemia is defined as baseline oxygen saturation measured by pulse oximetry at rest ≤92.
  • Severe hypoxemia is defined as oxygen saturation at rest ≤85.
  • Hypoxia refers to inadequate tissue oxygenation that may be present in the setting of chronic hypoxemia.
  • Cyanosis is blue or purple discoloration of the skin, lips, and nailbeds at oxygen saturation levels ≥5 g/dL of desaturated hemoglobin; It is visible in patients with chronic hypoxemia and normal or high hemoglobin levels but may be absent in patients with anemia.
NYHA functional classification system

Functional capacity:

  1. Patients with cardiac disease but resulting in no limitation of physical activity: Ordinary physical activity does not cause undue fatigue, palpitation, dyspnea, or anginal pain.
  2. Patients with cardiac disease resulting in slight limitation of physical activity: They are comfortable at rest. Ordinary physical activity results in fatigue, palpitation, dyspnea, or anginal pain.
  3. Patients with cardiac disease resulting in marked limitation of physical activity: They are comfortable at rest. Less than ordinary activity causes fatigue, palpitation, dyspnea, or anginal pain.
  4. Patients with cardiac disease resulting in inability to carry on any physical activity without discomfort: Symptoms of heart failure or the anginal syndrome may be present even at rest. If any physical activity is undertaken, discomfort increases.
Pulmonary arterial hypertension

Pulmonary arterial hypertension is defined as:

  • Mean pulmonary artery pressure by right heart catheterization ≥20 mm Hg and a pulmonary capillary wedge pressure ≤15 mm Hg; and pulmonary vascular resistance ≥2 Wood units.

Pulmonary arterial hypertension risk categories are measure using the 3-strata risk score calculator.
Shunt (hemodynamically significant shunt)

An intracardiac shunt is considered hemodynamically significant if there is evidence of chamber enlargement distal to the shunt and/or evidence of sustained Qp:Qs ratio ≥1.5.

An intracardiac shunt not meeting these criteria would be described as small or trivial.

Modified with permission from Stout el aL Copyright 2018 American Heart Association, Inc. and American College of Cardiology Foundation.
ACHD indicates adult congenital heart disease; AP, anatomic and physiological; ICD, Implantable cardioverter-defibrillator; NYHA, New York Heart Association; and Qp:Qs, pulmonary-to-systemic blood flow ratio.
ASD indicates atrial septal defect; BNP, B-type natriuretic peptide; ICD, implantable–cardioverter defibrillator; NT-proBNP, N-terminal prohormone of B-type natriuretic peptide; NYHA, New York Heart Association; PDA, patent ductus arteriosus; TGA, transposition of the great arteries; and VSD, ventricular septal defect.