A Segmental Approach to Congenital Heart Disease

A practical radiology review of A Segmental Approach to Congenital Heart Disease, focused on imaging findings, differential diagnosis, reporting points, and high-yield teaching pearls.

• Concept & Logic

Think of heart as a 3-level house

1. Atria (visceroatrial situs)

2. Ventricles (ventricular loop)

3. Great arteries (conotruncus)

Two “staircases”

• AV junction (atrioventricular)
• VA junction (ventriculoarterial)
• Each level = a segment, each staircase = a connection.
• Described using segmental set {S,D,S}
• 1st letter = situs
• 2nd = ventricular loop
• 3rd = great arterial relationship

Stepwise Diagnostic Logic

• Identify each major segment (atria, ventricles, great arteries).
• Define how each connects to the next.
• Note associated anomalies (valves, septa, vessels).
• Assess function/physiology of the whole system.

Atrial Identification

• Right Atrium (RA) = systemic venous atrium
• Receives IVC + SVC + coronary sinus
• Triangular broad-based appendage
• Pectinate muscles extend to AV junction
• Left Atrium (LA) = pulmonary venous atrium
• Receives pulmonary veins only
• Narrow tubular appendage
• No pectinate muscle extension
• If unclear situs ambiguous

Key rule: “ The chamber receiving IVC is morphologic RA ”

Ventricular Identification

Right Ventricle (RV)

• Moderator band connects septum ↔ free wall
• #Tricuspid valve more apical
• Has infundibulum/conus → no fibrous continuity between AV & semilunar valves

Left Ventricle (LV)

• Smooth septum, no moderator band
• #Mitral valve more cranial
• No conus → fibrous continuity between AV & semilunar valves
• AV valves follow the ventricle, not the atrium!
• Tricuspid → RV (septophilic)has papillary muscle attachments to
• the right ventricular septal surface
• Mitral → LV (septophobic)only attaches to the free wall of
• the left ventricle

Great Arterial Identification

• Pulmonary artery (PA) → branches to lungs only
• Aorta (Ao) → branches to body + coronaries
• Common trunk (Truncus Arteriosus) → gives both → mark as X (undetermined)
• Aortic annulus = posterior & right of pulmonary annulus in solitus {S,D,S}
• Identify aorta by coronary origin

Key Radiologic Principles

• “Right” and “Left” = morphology, not body side.
• Segmental logic ensures consistent terminology across all caregivers.

Morphologic recognition on CT/MRI → based on connections & appendages, not chamber position.

• Second Major Segment: Ventricular Loop
• Loop direction = defines ventricular position
• loop bulboventricular loop to the right → RV lies anterior + right of LV
• loop bulboventricular loop to the left → RV lies anterior + left of LV
• Remember: loop direction determines spatial arrangement, not morphology.
• Third Major Segment: Great Arterial Relationship
• Normal (Solitus, S) → Aorta = posterior, inferior, right of PA
• Inversus (I) → Aorta = posterior + left of PA

Malpositions

• malposition → Aorta right of PA
• malposition → Aorta left of PA
• “Any non-solitus/non-inversus relation = malposition.”

First Connecting Segment: Atrioventricular (AV) Junction

• Biventricular AV Connections
• Concordant (RA→RV, LA→LV)
• Discordant (RA→LV, LA→RV)
• Straddling AV valve → tethered to opposite ventricle
• Overriding AV valve → annulus crosses septum

5. Overriding + Straddling

6. Balanced common AV canal (two similar ventricles)

• Univentricular AV Connections

1. Mitral atresia (unilateral left)

2. Tricuspid atresia (unilateral right)

3. Double inlet LV

4. Double inlet RV

5. Left-dominant common AV canal

6. Right-dominant common AV canal

Functional logic

• One functional ventricle → other acts as small outflow chamber.
• Single LV → bulboventricular foramen → small anterior RV outlet.
• Single RV → septal band + rudimentary posterior LV.

Second Connecting Segment: Conotruncus / Ventriculoarterial Junction

• Conal Development = Key to Outflow Anatomy
• Subpulmonary conus develops, subaortic resorbs →
• Ventriculoarterial concordance (normal)
• Ao posterior-right in D-loop (solitus)
• Ao posterior-left in L-loop (inversus)
• Subaortic conus develops, subpulmonary resorbs →
• Transposition (VA discordance)
• LV→PA, RV→Ao
• D-loop = D-malposition
• L-loop = L-malposition
• Both coni persist → Double outlet RV (DORV)
• Both great vessels from RV
• VSD position varies
• Both coni resorbed → Double outlet LV (DOLV)
• Special case: Anatomically corrected malposition → Ao above LV, PA above RV (but malposed).
• Conal septal malalignment →
• Anterior → TOF (infundibular stenosis)
• Posterior → subaortic stenosis / interrupted arch

Evaluation of Associated Anomalies

• Always screen for valve, septal, venous, and arterial anomalies
• Atrial/Ventricular septa
• AV & semilunar valves
• Aorta, PA branches
• Pulmonary & systemic veins

Evaluation of Function

Functional classification

• Pressure overload → stenosis, coarctation, branch PA stenosis
• Volume overload → regurgitation, L→R shunts
• Intermixing → O₂-mixing before systemic flow (e.g. common chamber, R→L shunt)
• Poor contractility → cardiomyopathy, ischemia
• Final integration: Combine morphology + function → guide medical or surgical management.