# Coronary CT Angiography and Anatomy

> Coronary CTA for NEET-PG Radiology: coronary anatomy and dominance, plaque types, CAD-RADS, gating and heart rate control and anomaly assessment.

- Canonical URL: https://prepelephant.com/topics/neet-pg/radiology/cta-coronary-anatomy
- Exam / course: NEET-PG · Subject: Radiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Coronary CT Angiography and Anatomy", PrepElephant, https://prepelephant.com/topics/neet-pg/radiology/cta-coronary-anatomy

## Direct answer

Coronary CT angiography images the coronary lumen and wall on an ECG-gated contrast scan, after heart-rate control to under about 60 beats per minute with beta blockers and sublingual nitrates to dilate the vessels. Anatomy first: the left main artery divides into the left anterior descending artery, which runs the anterior interventricular groove giving septal and diagonal branches, and the left circumflex, which runs the atrioventricular groove giving obtuse marginal branches; the right coronary artery supplies the SA and AV nodes and, in about 85 per cent of hearts that are right-dominant, ends as the posterior descending artery. CTA's strength is a very high negative predictive value for excluding obstructive disease in low-to-intermediate risk chest pain, with plaque described as calcified, non-calcified or mixed, stenosis graded and reported under CAD-RADS, and anomalies such as an interarterial (malignant) course defined by the scan.

## What you must remember

- **Dominance:** right-dominant about 80-85 per cent (RCA gives the posterior descending artery), left-dominant roughly 8-10 per cent, codominant the remainder; the PDA supplier defines dominance, not vessel size.
- **Branch map:** LAD — septal perforators and diagonals (anterior wall, apex, septum); LCx — obtuse marginals (lateral wall); RCA — acute marginals, then PDA and posterolateral branches in right dominance (inferior wall, nodes).
- **Rate control:** beta blockers targeting under 60 bpm plus sublingual nitrate; prospective ECG triggering (step-and-shoot) slashes dose versus retrospective spiral, which is reserved for arrhythmia or high rates.
- **Plaque reading:** calcified plaque may bloom and overstate stenosis; non-calcified plaque with low attenuation, spotty calcification and positive remodelling marks vulnerability; stenosis is graded and assigned a CAD-RADS category from 0 (none) to 5 (total occlusion) with modifiers for stents, grafts and poor quality.
- **Calcium score context:** Agatston scoring on non-contrast CT stratifies risk (0 highly reassuring, above 300 high risk) and CTA is interpretatively limited by heavy calcification.
- **Anomalies that matter:** a coronary artery coursing between aorta and pulmonary artery (interarterial, malignant course) causes sudden death in the young; coronary-cameral fistula and anomalous origin from the pulmonary artery (ALCAPA) are the other exam names.
- **Where CTA sits:** first-line for low-to-intermediate probability stable chest pain and for anomalous coronary assessment; invasive angiography remains the road to intervention in high probability or positive CTA cases.

## Reading one gated study

A 48-year-old woman has atypical chest pain and a positive treadmill test; pre-test probability is intermediate. After oral metoprolol brings the rate to 56, prospective gating covers the heart in one or two heartbeats. The left main and LAD are widely patent; a mixed plaque in the mid-LAD causes about 40 per cent stenosis — CAD-RADS 2, managed medically with risk-factor control. The circumflex and dominant RCA are normal, the PDA arising from the RCA — right dominance, relevant if she ever needs grafting.

The second case is a 26-year-old cyclist with exertional syncope. CTA shows the left coronary artery arising from the right sinus and passing between the aortic root and the pulmonary trunk — an interarterial, malignant course — which explains exertional events through slit-like compression and is a surgical indication regardless of symptoms. The third is a post-bypass patient: mammary and venous grafts are traced along their whole lengths for patency, anastomotic stenosis and competitive flow — a specific CTA indication with its own protocol.

## Where students slip

Dominance is the reliable trap: candidates define it by which artery is bigger, but the definition is which vessel gives the posterior descending artery — the exam asks exactly this sentence. The second slip is overcalling stenosis from calcium bloom, the reason heavy calcification downgrades CTA in favour of functional testing or invasive angiography. Third, plaque composition: non-calcified low-attenuation plaque is the dangerous one, and quoting "spotty calcification and positive remodelling" as vulnerable-plaque markers earns viva credit. Indian framing: early-onset coronary disease is common, so anomalous-coronary and non-calcified-plaque questions surface in younger vignettes; scanners are widespread but prospective gating with rate control is what separates a diagnostic from a nondiagnostic study in busy government-catering departments, and the exam expects you to state how rate and rhythm — not the scanner — determine image quality.

## Frequently asked questions

### How is coronary dominance determined?

By the artery that gives rise to the posterior descending artery — the right coronary in about 80-85 per cent of hearts, the left circumflex in 8-10 per cent, and codominance otherwise.

### Why are beta blockers and nitrates given before coronary CTA?

Beta blockers bring the heart rate below about 60 beats per minute to freeze coronary motion, and nitrates dilate the vessels to improve lumen assessment.

### Which plaque features suggest vulnerability on CTA?

Low-attenuation non-calcified plaque, spotty calcification and positive remodelling mark plaques prone to rupture.

### What is the CAD-RADS system?

A standardised reporting scale from 0 to 5 grading coronary stenosis severity on CTA, with modifiers for stents, bypass grafts and nondiagnostic segments.

### Why is an interarterial coronary course called malignant?

A coronary artery passing between the aorta and pulmonary artery can be compressed during exercise, causing ischaemia and sudden cardiac death in young patients, warranting surgical correction.