A Practical Approach to Fetal Cardiac Screening
The Three Vessel Trachea (3VT) view is not a diagnostic plane โ
it is a screening plane that detects abnormal patterns.
When the 3VT view looks unusual,
the goal is not to jump to a diagnosis,
but to identify which pattern is abnormal.
โ Step 1: Know the Normal Pattern
In a normal 3VT:
- Pulmonary artery (largest)
- Aorta (slightly smaller)
- Superior vena cava (smallest)
PA and Ao form a characteristic V-shape
to the left of the trachea.
If this V-pattern is disturbed,
something deserves further evaluation.
๐จ Step 2: Recognize the Abnormal Pattern
1๏ธโฃ Ao Dominance (PA smaller than Ao)
Appearance: Asymmetric V-shape
Think about:
- Tetralogy of Fallot
- Severe pulmonary stenosis
- Pulmonary atresia
๐ Check RVOT flow carefully.
2๏ธโฃ Very Small or Absent PA
Appearance: PA barely visible
Think about:
- Pulmonary atresia
๐ Look for ductal retrograde filling.
3๏ธโฃ Parallel Great Vessels
Appearance: Loss of V-shape
Think about:
- DORV
- Transposition variants
๐ Confirm LVOT connection.
4๏ธโฃ Single Large Vessel (2-vessel appearance)
Appearance: Only two vessels seen
Think about:
- Truncus arteriosus
๐ Trace both outflow tracts.
5๏ธโฃ U-shape Around the Trachea
Appearance: Trachea between two vessels
Think about:
- Right aortic arch
๐ Check descending aorta position.
6๏ธโฃ Complete Ring Appearance
Appearance: Trachea fully encircled
Think about:
- Double aortic arch
๐ Confirm in sagittal view.
๐ง Practical Algorithm
When 3VT looks abnormal, ask:
- Is PA size normal?
- Is the V-shape preserved?
- Where is the trachea?
- Is there antegrade RVโPA flow?
- Are great vessels aligned normally?
๐ฅ Bottom Line
The 3VT view does not give a diagnosis.
It gives a direction.
Abnormal patterns guide the next step โ
LVOT, RVOT, Doppler, and arch evaluation.
