Map the pulmonary veins (number, ostia, common trunks, early branching), exclude left atrial appendage thrombus on a delayed phase, and note the oesophagus behind the posterior wall.
Orient first
- Four ostia is the usual pattern; a left common trunk and a right middle vein are frequent variants.
- Appendage filling defects on the first pass are often slow mixing, not thrombus — a delayed phase settles it.
- After ablation, pulmonary vein stenosis is the complication imaged.
Acquire the study
- ECG-gated CT angiography of the left atrium, then a 60-second delayed acquisition through the appendage; 3D volume-rendered and endoluminal reformats.
The manoeuvre
- Count the veins on each side; name variants — common trunk, accessory right middle vein, early branching (< 1 cm from the ostium).
- Ostial diameters in mm in two orthogonal planes perpendicular to each vein.
- Left atrial appendage: morphology and filling on the arterial phase, then on the delayed phase — persistent defect means thrombus.
- Posterior left atrial wall: oesophagus position and distance.
- Post-ablation: compare ostial diameters with the baseline — percentage narrowing.
What confirms it
- A persistent appendage filling defect on the delayed phase is thrombus; a variant is named with its ostial size.
What licenses you to exclude it
- Complete appendage opacification on the delayed phase excludes thrombus.
The classic misread
- Calling a mixing artefact thrombus without a delayed phase.
- Missing a right middle pulmonary vein, which changes the ablation lesion set.