CHD Imaging Basics - Pixel Peepshow
- Key Modalities:
- Chest X-ray (CXR): Initial screen; situs, cardiomegaly, pulmonary vascularity.
- Echocardiography: Primary diagnostic tool; anatomy & function.
- CT/MRI: Complex anatomy, extracardiac anomalies, post-op evaluation.
- CXR Clues:
- Cardiothoracic Ratio (CTR): > 0.5 (child >1yr), > 0.6 (neonate).
- Pulmonary Vascularity: Plethora (↑ shunt), Oligemia (↓ flow), Pulmonary Hypertension.
- Cardiac Silhouette: e.g., "boot-shaped" (TOF), "egg-on-string" (TGA).
- Diagnostic Pathway:
⭐ Systematic CXR: Situs (gas), CTR, Pulmonary Vascularity (MPA, fields), Great Arteries (arch), Chamber signs.
Acyanotic Shunts - Overload Orchestra
- L-R shunts (ASD, VSD, PDA): ↑Pulmonary Blood Flow (PBF) → plethora.
- Risk: Volume overload, Pulmonary HTN, Eisenmenger (R-L shunt, cyanosis).
- Specifics:
- ASD (Atrial Septal Defect):
- Ostium secundum common.
- CXR: RA/RV↑, PBF↑.
- Echo: Defect. Ausc: Wide, fixed S2.
- VSD (Ventricular Septal Defect):
- Membranous common.
- CXR: LA/LV/±RV↑, PBF↑.
- Echo: Defect. Ausc: Holosystolic murmur.
- PDA (Patent Ductus Arteriosus):
- Assoc. prematurity, rubella.
- CXR: LA/LV↑, PBF↑.
- Echo: Ductus. Ausc: Continuous machinery murmur.
- ASD (Atrial Septal Defect):
⭐ Most common CHD is VSD; most common ASD is ostium secundum.
Acyanotic Obstructions - Pressure Cookers
- Lesions causing pressure overload from restricted blood flow.
- Key differentiating features:
| Lesion | CXR Signs | Echocardiography |
|---|---|---|
| Coarctation of Aorta | '3' sign 📌, rib notching; Normal/↑heart size | Juxtaductal narrowing, pressure gradient |
| Aortic Stenosis (AS) | LVH, post-stenotic aortic dilatation | Valvular common; Thick valve, gradient >50 mmHg (severe) |
| Pulmonary Stenosis (PS) | RVH, post-stenotic main PA dilatation | Valvular common; Doming valve, gradient >40 mmHg (severe) |
⭐ Coarctation of Aorta is associated with Turner Syndrome and bicuspid aortic valve.
Cyanotic (↓PBF) - Blue & Dry
- ↓ Pulmonary Blood Flow (PBF) with cyanosis. Key conditions:
| Feature | Tetralogy of Fallot (TOF) | Tricuspid Atresia |
|---|---|---|
| Pathology | 📌 PROVe: Pulmonary Stenosis (RVOTO), RVH, Overriding Aorta, VSD | Agenesis of Tricuspid Valve, hypoplastic RV; ASD & VSD/PDA essential for survival |
| CXR | 'Boot-shaped' heart (Coeur en sabot), ↓PBF, clear lung fields | Normal/mild cardiomegaly, ↓PBF, prominent RA, concave PA segment |
 | ||
| ECG | RVH, Right Axis Deviation (RAD) | Superior QRS axis (LAD), LVH, RAE |
| Key Finding | RVOTO severity dictates cyanosis | Obligatory R-L shunt at atrial level |
Cyanotic (↑PBF) - Blue & Drenched
- Presents with cyanosis & ↑ pulmonary blood flow (PBF).
| Condition | CXR Appearance & Mnemonic | Key Echo Feature |
|--------------------|---------------------------------------------------------------|--------------------------------------------------------------------------|
| TGA | "Egg on a string" (narrow mediastinum), ↑PBF. 📌
| Aorta from RV (anterior), PA from LV (posterior). |
| TAPVR (Supracardiac) | "Snowman sign" (dilated SVC, vertical vein), ↑PBF. 📌 
| All pulmonary veins drain to RA/systemic veins. |
| Truncus Arteriosus | Cardiomegaly, ↑PBF, prominent pulmonary arteries. R-arch (30%). | Single trunk overrides VSD; supplies systemic, pulmonary, coronary arteries. |
High‑Yield Points - ⚡ Biggest Takeaways
- CXR is the first step: assess cardiac size, shape, pulmonary vascularity.
- Echocardiography is gold standard for CHD diagnosis and anatomy.
- Tetralogy of Fallot: classic "boot-shaped heart" on CXR.
- Transposition of Great Arteries (TGA): "egg-on-string" sign on CXR.
- TAPVR: "snowman sign" or "figure of 8" heart on CXR.
- Coarctation of Aorta: look for rib notching and "figure of 3 sign".
- Pulmonary vascularity on CXR helps differentiate shunt types; ↑ in L-R shunts, ↓ in R-L shunts or pulmonary stenosis.
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