Morphological Approach

Important definitions

• Levocardia: the heart is located in the left hemithorax, with the apex pointing to the left. 

• Levoposition: the heart is located in the left hemithorax due to displacement by an external (extrinsic) structure.

• Dextrocardia: the heart is located in the right hemithorax, with the apex pointing to the right. 

• Dextroposition: the heart is located in the right hemithorax due to displacement by an external (extrinsic) structure.

• Mesocardia: the heart is located centrally in the thorax, with the apex pointing downward. 

• Mesoposition: the heart is centrally located due to displacement by an external (extrinsic) structure. 

• Left aortic arch: the aortic arch is located above the left main bronchus. 

• Right aortic arch: the aortic arch is located above the right main bronchus.

Van Praagh Classification (Boston)

Since 1964, the van Praagh classification has been a segmental approach to describing congenital heart defects. It is based on a systematic analysis of the heart’s anatomy using the following principles: 

• Situs: Determination of the position of the atria and viscera (e.g., solitus, inversus, ambiguous) 

  • Refers to the location of the atria and abdominal/thoracic organs. Determines whether the arrangement is normal (situs solitus), mirror-image (situs inversus), or ambiguous (isomerism or undefined lateralization)

• Segmental alignment: The sequential relationship between the atria, ventricles, and great arteries 

  • Describes the progressive, sequential connection between heart segments: Which atrium connects to which ventricle (atrioventricular alignment)? Which ventricle gives rise to which great artery (ventriculo-arterial alignment)?

• Connections between segments: How each segment connects to the next (AV and VA connections: concordant, discordant, double outlet, etc.) 

  • Refers to the status, nature, and morphology of the junctional segments: 

    • Atrioventricular junction: the anatomical and functional characteristics of how the atria connect to the ventricles (e.g., normal valves, atresia, straddling, double inlet). 

    • Ventriculo-arterial junction: the anatomical and functional characteristics of how the ventricles connect to the great arteries (e.g., normal outflow tracts, double outlet, truncus arteriosus). 

    • This assessment includes whether the junctions are concordant, discordant, atretic, overriding, or malpositioned, and is essential for defining the complexity and type of congenital heart defect.

• Spatial relationships: Orientation of cardiac structures in space (right/left, anterior/posterior, etc.) 

  • Right, left, anterior, posterior, superior, inferior

• Associated anomalies: Structural or functional abnormalities that coexist with the segmental arrangement (e.g., VSD, outflow tract obstructions, etc.) 

  • Any congenital heart defect can be described using the segmental coding system, ensuring that the description includes both the **segmental alignments** and the **status of the connections** between segments.

This method provides a comprehensive anatomical framework for describing both normal and complex congenital heart anatomies.

References: 

1. Van Praagh R. The segmental approach to diagnosis in congenital heart disease. Birth Defects;1972:8:4. 

2. Van Praagh R. Editorial. Terminonlogy of congenital heart disease. Glossary and Commentary. Circulation 1977;56:139-143

Three cardiac segments (anatomical building blocks in the van Praagh classification): 

• Atria (oreillettes) Ventricles (ventricules)  - Atrial Situs:

  • S (Solitus): Normal arrangement. S: Situs solitus — the right atrium is on the right and the left atrium is on the left

  • I (Inversus): Mirror-image arrangement. I: Situs inversus — the right atrium is on the left and the left atrium is on the right 

  • A (Ambiguous): Indeterminate arrangement. A: Ambiguous atrial situs — uncertain atrial lateralization; bilateral "viscero-atrial symmetry" Can be associated with right isomerism (asplenia) or left isomerism (polysplenia).

  • The atrial situs usually corresponds to the abdominal and thoracic visceral situs. Segmental notation: { S, _ , _ } or { I , _ , _ } or { A , _ , _ } 

  • Note: Van Praagh did not support the concept of pure cardiac isomerism, unlike Anderson, who did.

• Ventricular Looping:

  • D (D-loop): Rightward looping; morphologic right ventricle on the right. D: d-loop — rightward cardiac loop; typically, the right ventricle is on the right and the left ventricle is on the left; 

  • L (L-loop): Leftward looping; morphologic right ventricle on the left. L: l-loop — leftward cardiac loop; typically, the left ventricle is on the right and the right ventricle is on the left

  • { _ , D , _ } or { _ , L , _ }. 

• Great vessels (gros vaisseaux) — i.e., the aorta and pulmonary artery 

  • Normal conus: The relative position of the great vessels (GV) is preserved, with the aortic valve (AoV) posterior to the pulmonary valve (PV). There is fibrous continuity between the AoV and atrioventricular (AV) valves. 

    • {_,_,S} (Solitus): AoV is posterior and to the right of the PV 

    • {_,_,I} (Inversus): AoV is posterior and to the left of the PV 

  • Abnormal conus: The aorta is anterior, indicating an abnormal position of the GV. There is discontinuity between the AoV and AV valves. 

    • {_,_,D} (Dextro): AoV is anterior and to the right of the PV, or both valves are side-by-side with AoV on the right 

    • {_,_,L} (Levo): AoV is anterior and to the left of the PV, or both valves are side-by-side with AoV on the left 

    • {_,_,A} (Anterior): AoV is directly anterior to the PV

• Two connecting segments (junctional components): 

  • Atrioventricular junction (canal atrioventriculaire) — connects the atria to the ventricles. Atrioventricular (AV) alignment – 5 types: 

    • AV concordance {S,D,_} or {I,L,_}: The right atrium connects to the right ventricle, and the left atrium to the left ventricle 

    • AV discordance {S,L,_} or {I,D,_}: The right atrium connects to the left ventricle, and the left atrium to the right ventricle 

    • Atresia of an AV valve: One AV valve is absent (e.g., tricuspid or mitral atresia) 

    • Overriding or straddling AV valve: An AV valve is positioned above and connected to both ventricles (overrides the septum) 

    • Double inlet ventricle (DIV): Both atria drain into the same ventricle (usually a morphologic left ventricle, but sometimes RV)

  • Infundibulum or conus arteriosus — connects the ventricles to the great arteries. Ventricular-Arterial junction.

    • Ventriculo-arterial (VA) alignment – 4 types: 

      • VA concordance {_,D,S} or {_,L,I}: The right ventricle gives rise to the pulmonary artery, and the left ventricle gives rise to the aorta — normal arrangement. 

      • VA discordance {_,D,D} or {_,L,L}: The right ventricle gives rise to the aorta, and the left ventricle gives rise to the pulmonary artery — as seen in transposition of the great arteries. 

      • Double outlet ventricle: Both great arteries arise from the same ventricle: DORV (Double Outlet Right Ventricle), DOLV (Double Outlet Left Ventricle) 

      • Single outlet ventricle: Only one great artery exits the heart, e.g., common arterial trunk (truncus arteriosus).

These segments and their connections are described in sequence to define the architecture and anomalies of the heart in congenital disease.

Each segment has distinct anatomical features that help identify it. For example: Atrial appendages and the moderator band (RV) are key distinguishing structures. The connection of veins is not reliable for identifying atrial morphology, as venous connections can be anomalous. However, the right atrium can often be identified by the opening of the coronary sinus, according to Stella van Praagh. In general (but not always), atrial situs and abdominal visceral situs are concordant.

Examples:

• {S,D,S}: Normal heart configuration

• {S,D,D}: Classic Dextro-Transposition of the Great Arteries (d-TGA)

• {I,L,I}: Mirror-image normal heart (situs inversus totalis and dextrocardia)

• {S,D,S}: A tricuspid atresia without transposition of the great arteries is still classified as {S,D,S}, because the segments are in their normal positions, but there is an anomaly at the right atrioventricular (AV) junction — specifically, absence of the tricuspid valve. Although the right atrium (RA) and right ventricle (RV) are aligned (S,D), they do not communicate. The same concept applies to pulmonary atresia: the RV is aligned with the pulmonary artery, but there is no flow due to atresia of the pulmonary valve. Key point: AV or VA concordance means that the segments are correctly aligned anatomically, but this does not guarantee functional communication between the structures.

• {S,D,D}: A classic double outlet right ventricle (DORV) with TGA physiology (Taussig-Bing anomaly) is also classified as {S,D,D}. This means: S: Situs solitus (normal atrial arrangement); D: D-loop (rightward ventricular looping — morphologic right ventricle on the right); D: Dextro-malposition of the great vessels. In this case: Both great arteries (the aorta and pulmonary artery) arise from the right ventricle (transposition of the great vessels). The aortic valve (VAo) is positioned anterior and to the right of the pulmonary valve (VP), indicating abnormal spatial arrangement.

• {S,L,L}: TGA {S,L,L} or l-TGA (congenitally corrected transposition of the great arteries): Situs solitus Levocardia (heart on the left with apex pointing left); Atrioventricular discordance (right atrium connects to left ventricle, left atrium to right ventricle); Ventriculo-arterial discordance (left ventricle connects to pulmonary artery, right ventricle to aorta); Aortic valve anterior and to the left of the pulmonary valve. This results in a physiologically corrected circulation despite the anatomical discordances.

• {S,L,L}: A single left-type ventricle classified as {S,L,L} is characterized by situs solitus and levocardia, with a morphologic left ventricle receiving inflow from both atria (double inlet configuration). The right ventricle is hypoplastic or replaced by a small outlet chamber, and there is ventriculo-arterial discordance, meaning the great arteries arise abnormally. Specifically, the aortic valve is positioned anterior and to the left of the pulmonary valve, originating from the outlet chamber. A ventricular septal defect (VSD) or bulbo-ventricular foramen (BVF) is typically present, allowing blood flow between chambers. This anatomical configuration results in a functionally univentricular circulation, with the left ventricle serving as the dominant systemic pump.

Anderson Classification (London).

This is the classification we locally use. We follow as well the international nomenclature. Anderson classification focuses on identifying the concordance or discordance between cardiac segments (atria, ventricles, great arteries). It is a highly descriptive approach that emphasizes the detailed morphology and connections of each cardiac structure. 

Key principles: 

• Rather than relying on a segmental code, it provides a structural description of: 

  • Atrial situs 

  • Ventricular topology (right/left morphology) 

  • Atrioventricular and ventriculo-arterial connections 

  • Valve morphology (e.g., separate vs. common AV valves, valve anomalies) 

This approach is particularly useful for surgical planning and for understanding complex congenital heart disease, as it focuses on the actual anatomy and not just segmental position.

Atrial segment

• Atrial situs solitus: the right atrium is on the right, and the left atrium is on the left (normal arrangement). 

• Atrial situs inversus: the right atrium is on the left, and the left atrium is on the right (mirror-image arrangement). 

• Right isomerism: both atria have the morphological features of a right atrium (often associated with asplenia). 

• Left isomerism: both atria have the morphological features of a left atrium (often associated with polysplenia).

Ventricular segment

• Biventricular heart: has two distinct ventricles with either right or left topology

• Univentricular heart: only one functional ventricle, which can be: Right-type (morphologic right ventricle); Left-type (morphologic left ventricle); Indeterminate (ventricle does not clearly resemble either morphology)

Atrioventricular junction

• Myocardial junction (Atrioventricular connection types): 

  • Biventricular AV connection: Both atria connect to separate ventricles 

    • Can be: Concordant (normal alignment); Discordant (atria connect to the opposite ventricles); Ambiguous (unclear or mixed features) 

  • Univentricular AV connection: Both atria connect to a single ventricle 

    • Can present as: Double inlet (both atria empty into one ventricle); Absence of one AV connection (either right or left AV valve is missing); 

  • Biventricular and uni-atrial connection: One atrium connects normally to a ventricle. The other atrium has no direct connection, and instead the permeable AV valve overrides or straddles the ventricular septum, connecting to both ventricles.

• Valvular Morphology

  • Right and left AV valves separated. Possible morphological abnormalities include: 

    • Stenotic: narrowed valve 

    • Imperforate (atretic): valve is completely closed or absent 

    • Regurgitant: valve is incompetent and allows backflow 

    • Overriding: valve is positioned over both ventricles 

    • Straddling: valve chordae and attachments extend into both ventricles

  • Common AV valve:

    • Stenotic, imperforate (atretic) right or left component, regurgitant, straddling.

Ventricular-Arterial junction

• Ventricular-arterial connection:

  • Concordant, discordant, double outlet ventricle, single outlet ventricle

  • Valvular morphology: 

    • Aortic and pulmonary valves separated: Stenotic, Imperforate, Regurgitant, Overriding 

    • Single semilunar valve: Stenotic, Regurgitant, Overriding

    • There is no straddling for semilunar valves, as they do not have chordae tendineae.

A normal heart has atrioventricular and ventriculo-arterial concordance; a mirror-image heart does as well. A classic transposition of the great arteries (TGA) has atrioventricular concordance but ventriculo-arterial discordance. This model recognizes isomerism—for example, a person can have two morphologically right atria.

Physiological classification

• Left-to-right shunt lesions 

  • Communication between the two circulations can occur at the atrial, ventricular, or arterial level. This promotes the flow of blood from the systemic to the pulmonary circulation, whether during systole, diastole, or continuously. Over time, this leads to increased pulmonary venous return, resulting in volume overload of the left heart chambers. However, in the case of an atrial septal defect (ASD), the right-sided chambers become overloaded, as the shunt occurs during diastole at the atrial level. Symptoms typically develop gradually and are often clinically silent in the immediate neonatal period. A murmur may become audible as pulmonary vascular resistance decreases.

  • Diastolic shunt: seen in atrial septal defect (ASD) 

  • Systolic shunt: seen in ventricular septal defect (VSD) 

  • Systolic–diastolic shunt: seen in patent ductus arteriosus (PDA), common arterial trunk (truncus arteriosus), complete atrioventricular canal (CAVC), and aortopulmonary window 

  • Symptoms typically emerge as pulmonary vascular resistance (PVR) decreases. In complete AV canal defects (CAVC), there may be early desaturation when elevated PVR promotes right-to-left shunting during the initial neonatal period.

  • Examples: Atrial septal defect, ventricular septal defect, atrioventricular canal, double outlet right ventricle without pulmonary stenosis, d-transposition of the great arteries with a large VSD, patent ductus arteriosus, common arterial trunk, aortopulmonary window.

• Cyanotic lesions 

  • Communication between the two circulations combined with an obstruction of the pulmonary outflow tract promotes the passage of blood from the pulmonary to the systemic circulation at the atrial or ventricular level, and rarely at the arterial level. 

  • Right-to-left shunting at the arterial level is generally due to pulmonary hypertension. 

  • These lesions cause obligatory mixing of the two circulations. 

  • They are typically recognized in the neonatal period by desaturation, with or without a murmur.

  • Atrial level: ASD/PFO with severe pulmonary stenosis, Ebstein anomaly 

  • Arterial level: Patent ductus arteriosus (PDA) with pulmonary hypertension 

  • Lesions causing obligatory mixing of the two circulations: d-Transposition of the great arteries (d-TGA), total anomalous pulmonary venous return (TAPVR), tricuspid atresia, single ventricle physiology

  • Examples: Tetralogy of Fallot, severe pulmonary stenosis with ASD or VSD, d-transposition of the great arteries, severe Ebstein anomaly, double outlet right ventricle with pulmonary stenosis, single ventricle with pulmonary stenosis, total anomalous pulmonary venous return, tricuspid atresia, persistent left superior vena cava draining into the left atrium, any congenital heart defect combining a VSD with obstruction of the pulmonary outflow tract.

• Obstructive lesions 

  • Lesions with partial obstruction to blood flow at the level of a valve, above a valve, or below a valve. 

  • They are rarely symptomatic unless the obstruction is severe or critical. 

  • In the neonatal period, they are typically identified by the presence of a heart murmur.

  • Examples: Mitral or supramitral stenosis, aortic stenosis (valvular, subvalvular, supravalvular), coarctation of the aorta, pulmonary stenosis (valvular, subvalvular, supravalvular), tricuspid stenosis (rare)

• Lesions with univentricular physiology 

  • Only one ventricle is well developed.

  • There is obligatory mixing of the pulmonary and systemic circulations at the atrial and/or ventricular level.

  • This condition is typically identified in the neonatal period by possible desaturation, a murmur, and often a hyperdynamic precordium.

  • Palliative surgeries will eventually be required to separate the two circulations and use the well-developed ventricle as the systemic pump. Ultimately, systemic venous return will be diverted away from the heart and connected directly to the pulmonary arteries.

  • Example: DORV with hypoplastic left or right ventricle, single left-type ventricle or DILV, hypoplastic left heart syndrome, pulmonary atresia with intact ventricular septum and hypoplastic right ventricle, tricuspid atresia, unbalanced atrioventricular canal.

• Low cardiac output lesions 

  • CO = SV x HR

  • SV influenced by preload, contractility, afterload

  • Increased afterload: Obstruction of the systemic ventricle, including: Hypoplastic left heart syndrome; Severe aortic stenosis; Severe coarctation of the aorta; Restrictive VSD in certain lesions. 

  • Decreased contractility: Myocarditis, dilated cardiomyopathy (DCMP) 

  • Decreased preload: Hypovolemia, cardiac tamponade, severe mitral stenosis, or restrictive ASD in certain conditions

  • Examples of low cardiac output lesions: Critical aortic stenosis, severe coarctation of the aorta, interrupted aortic arch, severe mitral stenosis, hypoplastic left heart syndrome, obstructed total anomalous pulmonary venous return (TAPVR), single ventricle with restrictive VSD, dilated cardiomyopathy. Restrictive ASD may be equivalent to mitral stenosis in certain lesions. 

  • TAPVR can be obstructed at the site of venous connection—most commonly in the infracardiac (infradiaphragmatic) type, and less frequently in the supracardiac type. Obstruction can also occur at the foramen ovale. In that case, the pulmonary venous return is not obstructed per se, but there is a reduction in left ventricular preload.

• PDA dependent lesions:

  • Lesions with systemic circulation dependent on the ductus arteriosus 

  • Lesions with pulmonary circulation dependent on the ductus arteriosus

  • For pulmonary circulation:

    • Any severe obstruction of the pulmonary outflow tract in the absence of significant aortopulmonary collaterals. In these cases, the ductus arteriosus supplies pulmonary blood flow from the aorta via a left-to-right (L→R) shunt.

    • Examples: Critical pulmonary stenosis, pulmonary atersia with TOF or without VSD, severe TOF, Tricuspid atresia with severe pulmonary stenosis or with a very restrictive ventricular septal defect (in the absence of TGA), double outlet right ventricle (DORV) with severe pulmonary stenosis.

  • For systemic circulation: Any severe obstruction of the left ventricular outflow tract. Here, the ductus arteriosus provides systemic blood flow from the pulmonary artery via a right-to-left (R→L) shunt. It is essential to maintain elevated pulmonary vascular resistance (PVR) to promote this shunting. This is referred to as a vicariant ductus (serving as an alternative route).

    • Examples: Hypoplastic left heart syndrome, critical aortic stenosis, severe coarctation of the aorta or interrupted aortic arch, tricuspid atresia with TGA and a very restrictive VSD or severe aortic stenosis and/or coarctation of the aorta, double outlet right ventricle (DORV) with aortic stenosis and/or severe coarctation.

A single lesion can be classified into two different categories based on its physiological characteristics.

• Rudolph AM. Congenital Diseases of the Heart: Clinical-Physiological Considerations. 3rd ed. Hoboken (NJ): Wiley-Blackwell; 2009. 

• Alboliras ET, Hijazi ZM, Lopez L, Hagler DJ, editors. Visual Guide to Neonatal Cardiology. Hoboken (NJ): Wiley; 2018.

Morphology of Atriums

• Rudolph AM. Congenital Diseases of the Heart: Clinical-Physiological Considerations. 3rd ed. Hoboken (NJ): Wiley-Blackwell; 2009. 

• Alboliras ET, Hijazi ZM, Lopez L, Hagler DJ, editors. Visual Guide to Neonatal Cardiology. Hoboken (NJ): Wiley; 2018.

Diagnostic Hierarchy of Congenital Heart Defects by the IPCCC