Echocardiography and Cardiac MR are foundational for diagnosing CHD, but Cardiac CT serves an essential, complementary role — and is the preferred advanced modality when MR is contraindicated (e.g. pacemakers) or unavailable.
1 Strengths
CT’s exceptionally high spatial resolution allows for the evaluation of very small anatomical structures, making it the best test to define:
- Coronary artery anomalies
- Aortopulmonary collateral arteries (MAPCAs)
- Complex extracardiac vascular abnormalities
Modern multidetector and dual-source scanners can image the entire heart in mere seconds — a meaningful advantage in young children where breath-holding and motion are non-starters.
2 Patient preparation
Young children may require sedation to remain still.
Beta-blockers improve image quality by lowering the heart rate, but evolving ultrafast CT technology increasingly allows imaging without beta-blockade — preserving the ability to evaluate intracardiac defects and coronaries.
Used for coronary evaluation, but must be strictly avoided if the patient is using phosphodiesterase inhibitors (e.g. sildenafil/Viagra) to prevent fatal hypotension.
3 ACHD AP classification
Adult CHD is frequently stratified using the ACHD AP classification system, which grades:
- Anatomical complexity of the defect — e.g. repaired Tetralogy of Fallot is Grade II; unrepaired is Grade III
- Physiological stage (A through D) — based on hemodynamics, valvular/ventricular dysfunction, and arrhythmias
This dual axis dictates the level of subspecialty care needed and the surveillance interval.
4 Post-processing
Diagnosing complex congenital defects heavily relies on post-processing the CT data. Routine tools:
- Oblique planar reconstructions — chase a tortuous baffle or conduit
- Maximum intensity projections (MIP) — bright vessels, shunts
- 3D volume rendering — understand the complex spatial relationships of shunts, baffles, and conduits
See Reconstruction views (MPR, MIP, VR) for the general primer on these reformats.