Normal coronary anatomy

Your internal compass

Identify a coronary by where it runs—not only by where it starts

Coronary names are anchored to their myocardial grooves. The LAD runs in the anterior interventricular groove, the LCx in the left atrioventricular groove, and the RCA in the right atrioventricular groove. This remains useful when origins are anomalous.

Do not learn the tree as a flat diagram. On CT, each artery spirals across a moving three-dimensional heart. Trace from ostium to the smallest assessable distal segment, confirming the vessel in axial images and multiplanar reformats.

A repeatable first pass

Trace the same way in every examination

1. Confirm cardiac orientation, situs, aortic root, pulmonary trunk, atria, ventricles, and interventricular grooves.
2. Find the right and left coronary ostia on thin axial images at the sinuses of Valsalva.
3. Trace the RCA through the right AV groove to the crux; identify conus, SA nodal, acute marginal, PDA, and posterolateral branches.
4. Trace the left main to its division; identify LAD, LCx, and a ramus intermedius if present.
5. Follow LAD to the apex, noting diagonals and septal perforators.
6. Follow LCx in the left AV groove, noting obtuse marginal branches and its distal reach.
7. Determine dominance from the origin of the PDA—not from which artery looks larger.
8. Review coronary veins and all noncoronary cardiac/extracardiac structures.

The starting landmark

Aortic root, sinuses, and coronary ostia

The aortic root contains three sinuses: right coronary, left coronary, and noncoronary. The RCA usually arises from the right coronary sinus; the left main from the left coronary sinus. The noncoronary sinus usually has no coronary origin.

• Ostial level: normally near the upper third of the sinus, below or around the sinotubular junction.
• Take-off: a normal coronary leaves the aortic wall without a long intramural segment and generally at a non-acute angle.
• Separate origins: conus or SA nodal branches may have an independent ostium; LAD and LCx can rarely arise separately without a left main.
• Before calling an anomaly: inspect the entire root in multiple planes and exclude motion, partial volume, or an unusually short left main.

Right coronary system

RCA: right AV groove to the crux

The RCA arises from the right sinus, passes between the right atrial appendage and right ventricular outflow region, then follows a C-shaped course in the right atrioventricular groove toward the inferior surface and crux.

Divide RCA descriptively into proximal, mid, and distal segments. The exact landmarks are less important than consistent, unambiguous communication—especially near the acute margin and PDA origin.

Left coronary gateway

Left main: short vessel, high consequence

The left main coronary artery (LM) passes between the left atrial appendage and pulmonary trunk before dividing. It usually bifurcates into LAD and LCx; a trifurcation adds a ramus intermedius.

• Normal bifurcation: LM → LAD + LCx.
• Trifurcation: LM → LAD + ramus intermedius + LCx. The ramus arises between LAD and LCx and supplies an anterolateral territory.
• Absent LM: separate LAD and LCx ostia from the left sinus; describe clearly rather than implying occlusion.
• Short LM: confirm on thin axial and oblique planes; do not mistake early branching for plaque or an anomalous origin.

Anterior interventricular artery

LAD: diagonals to the free wall, septals into the septum

The LAD descends in the anterior interventricular groove toward the apex. It often wraps around the apex to a variable degree. Its two major branch families point in different directions.

For segment naming, proximal LAD extends from the LM to the first large septal branch; mid LAD continues toward the second diagonal region; distal LAD runs beyond. In practice, describe lesions with both vessel segment and a nearby branch landmark—“mid LAD just distal to D1”—because branch patterns vary.

Left atrioventricular groove

LCx: obtuse marginals and the route to left dominance

The LCx turns left and posteriorly in the left AV groove beneath the left atrial appendage. Its obtuse marginal (OM) branches descend over the lateral/posterolateral LV wall.

• Proximal LCx: from left main to the first substantial OM.
• Distal LCx: continues in the AV groove beyond the first OM; calibre and reach depend strongly on dominance.
• OM branches: usually numbered by order of origin; identify the clinically meaningful branch rather than forcing every tiny branch into a number.
• Left dominance: LCx continues to the crux and gives the PDA, often with left posterolateral branches.

The LCx can be partially hidden by the left atrial appendage on 3D views. Confirm its origin and proximal course with axial/MPR images before declaring it absent.

Find the crux

Dominance is determined by the PDA origin

The cardiac crux is the junction of the AV groove and posterior/inferior interventricular groove. Trace the PDA backward from that groove to its parent artery.

Common language

The SCCT-adapted 18-segment coronary model

Numbering helps datasets and structured reporting, but the 2026 SCCT guidance recommends intuitive anatomical descriptors—such as “proximal LAD”—rather than segment numbers alone, especially around bifurcations. Branch patterns do not always fit the model perfectly.

Artery to myocardium

Territories are a map with overlap—not a rigid border

The AHA 17-segment myocardial model is useful for perfusion correlation, but the apical cap and border zones have the greatest variability. When a perfusion defect does not fit the “usual” artery, return to the patient’s actual coronary anatomy.

Variation is expected

Common normal variants to recognise and describe

• Separate conus artery (“third coronary”) or separate SA nodal artery.
• Short or absent left main with separate LAD and LCx ostia.
• Ramus intermedius from an LM trifurcation.
• One or several diagonal and obtuse marginal branches of variable calibre.
• Large first diagonal with a relatively small continuing LAD.
• Distal LAD wrapping around the apex—or terminating before it.
• Right-, left-, or co-dominant posterior circulation.
• Small-calibre nondominant RCA or LCx that is normal for that dominance pattern.

A variant becomes clinically important when it affects intervention, surgical planning, myocardial territory, or could be mistaken for occlusion. “Not seen” should trigger a search for an alternative origin or course before “occluded.”

The return circulation

Cardiac veins converge on the coronary sinus

Venous anatomy matters for cardiac resynchronisation therapy, electrophysiology procedures, retrograde cardioplegia, and surgical planning. A coronary venous phase may be required when detailed mapping—not routine arterial CTCA—is the clinical question.

Match view to question

How each reconstruction helps

Anatomy reporting

A compact routine that prevents omissions

1. State image quality and any non-evaluable segment.
2. State ostial origins and coronary dominance.
3. Describe LM division and major variants such as ramus intermedius or separate LAD/LCx origins.
4. Report each major artery in order—LM, LAD/diagonals, LCx/OMs, RCA/PDA/PLV—with intuitive segment names.
5. Describe anomalous origin, course, or termination separately and completely.
6. Include cardiac and extracardiac findings visible in the dataset.

Example anatomy line: “Conventional origins. Right-dominant circulation. LM bifurcates into LAD and LCx. Two diagonal and two obtuse marginal branches are present; RCA gives the PDA and two posterolateral branches.”

Trace before naming

Mini anatomy cases

Case A · A vessel arises between LAD and LCx and runs over anterolateral LV

If it originates directly at the left-main trifurcation, it is a ramus intermedius—not D1 or OM1.

Case B · PDA arises from RCA; large LCx supplies posterolateral LV

This is commonly described as co-dominant: specify RCA-derived PDA and LCx-derived posterolateral branches.

Case C · Two adjacent ostia in the left sinus; no LM trunk

Trace each. Separate LAD and LCx origins can be a benign variant; do not label the absent short trunk as LM occlusion.

Case D · Vessel in posterior interventricular groove

Location identifies the PDA. Trace proximally to RCA or LCx to determine dominance.

Case E · Vessel in anterior interventricular groove appears venous

The LAD and great cardiac vein run together. Follow direction and connections: the vein turns into the left AV groove and drains to the coronary sinus.

Active recall

Self-test: answer before opening

Printable quick revision

One-page coronary anatomy card

• LM: bifurcation LAD + LCx; trifurcation adds ramus.
• LAD: anterior groove to apex; D branches out, septals dive in.
• LCx: left AV groove; OMs descend on lateral LV.
• RCA: right AV groove; conus, nodal, acute marginal, then crux branches.
• Right dominance: PDA from RCA. Left: PDA from LCx.
• Venous pairings: great vein–LAD; middle vein–PDA; coronary sinus–posterior AV groove–RA.
• Views: axial truth + curved continuity + perpendicular lumen + VRT orientation.
• Final rule: origin → course → branches → termination; never infer identity from one image.

Provenance

Sources and scope

This chapter follows the Webinar 3 normal coronary anatomy talk, approximately 00:15–17:39. Automated captions contain transcription errors; anatomy and terminology were checked against current professional guidance.

1. SCCT Interpretation and Reporting of CCTA: 2026 Update — coronary definitions, 18-segment model, dominance, myocardial territories, multiplanar interpretation, and reporting.
2. SCCT scientific document hub: CCTA interpretation and reporting — current structured interpretation principles.
3. AHA standardized myocardial segmentation and nomenclature — 17-segment myocardial model and coronary-territory variability.

Educational material only. Branch number, dominance terminology, and segment boundaries can vary by convention; use intuitive anatomical descriptions and local structured-reporting policy. External references require internet; this chapter works offline.