DOI:10.2214/AJR.06.1295
AJR 2007; 188:1665-1674
© American Roentgen Ray Society
Normal and Variant Coronary Arterial and Venous Anatomy on High-Resolution CT Angiography
Sunil Kini1,2,
Kostaki G. Bis2 and
Leroy Weaver2,3
1 Present address: Quantum Medical Radiology, Atlanta, GA 30339.
2 Department of Diagnostic Radiology, William Beaumont Hospital, 3601 W 13 Mile
Rd., Royal Oak, MI 48073.
3 Present address: Elkhart General Healthcare System, Elkhart, IN 46514.
Received September 30, 2006;
accepted after revision January 15, 2007.
Address correspondence to K. G. Bis
(kbis{at}beaumont.edu).
CME
This article is available for CME credit. See
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for more information.
FOR YOUR INFORMATION
This article is available for CME credit. See
www.arrs.org
for more information.
Abstract
OBJECTIVE. This article displays the normal and variant anatomy of
the coronary arteries and subjacent cardiac veins using a high-resolution
64-MDCT scanner.
CONCLUSION. Knowledge of the anatomy of the coronary arteries and
subjacent cardiac veins as displayed with maximum intensity and
volume-rendered projections is important for correct image interpretation of
coronary CT angiography examinations.
Keywords: anatomy • anomalies • arteriography • cardiac imaging • coronary arteries • CT angiography • heart • MDCT
Introduction
Contrast-enhanced CT angiography (CTA) of the coronary arteries is becoming
feasible as temporal and spatial resolution improves with the availability of
MDCT. Detection, characterization, and quantification of coronary artery
disease and elegant delineation of coronary anatomy are possible using 2D
multiplanar reformation (MPR), 3D maximum-intensity-projection (MIP), and 3D
volume-rendered postprocessing techniques. Familiarity with coronary artery
and venous anatomy and anatomic variants is important for correct image
interpretation. This anatomy and the arterial variants have been well
described using conventional angiographic techniques
[1,
2]. However, the
cross-sectional nature of CT has the benefit of more precisely displaying the
spatial relationships of coronary arterial and venous anatomy with respect to
cardiac structures. This article highlights this anatomy with a variety of MIP
and volume-rendered techniques (Figs.
1,
2A,
2B,
2C,
2D,
3A,
3B,
3C,
3D,
4A,
4B,
5A,
5B,
6,
7A,
7B,
7C,
8A,
8B,
8C,
9,
10,
11,
12A,
12B,
12C,
13,
14A,
14B,
15A,
15B,
16A,
16B,
17A,
17B,
18A,
18B,
18C).
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Fig. 1 —Anterior schematic diagram of heart shows course of dominant
right coronary artery and its tributaries. AV = atrioventricular, PDA =
posterior descending artery, RCA = right coronary artery, RV = right
ventricular, SA = sinoatrial.
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Fig. 2A —CT images of normal heart in 53-year-old man. Ao = aortic
root, CS = coronary sinus, LA = left atrium, LAD = left anterior descending
artery, LCx = left circumflex artery, LM = left main coronary artery, LV =
left ventricle, PDA = posterior descending artery, RA = right atrium, RCA =
right coronary artery, RV = right ventricle, RVOT = right ventricular outflow
tract. Axial 5-mm maximum-intensity-projection (MIP) image shows left main
coronary artery as it arises from left coronary cusp.
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Fig. 2B —CT images of normal heart in 53-year-old man. Ao = aortic
root, CS = coronary sinus, LA = left atrium, LAD = left anterior descending
artery, LCx = left circumflex artery, LM = left main coronary artery, LV =
left ventricle, PDA = posterior descending artery, RA = right atrium, RCA =
right coronary artery, RV = right ventricle, RVOT = right ventricular outflow
tract. Axial 5-mm MIP image shows right coronary artery as it arises from
right coronary cusp inferior to level of beginning of left main coronary
artery.
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Fig. 2C —CT images of normal heart in 53-year-old man. Ao = aortic
root, CS = coronary sinus, LA = left atrium, LAD = left anterior descending
artery, LCx = left circumflex artery, LM = left main coronary artery, LV =
left ventricle, PDA = posterior descending artery, RA = right atrium, RCA =
right coronary artery, RV = right ventricle, RVOT = right ventricular outflow
tract. Axial 5-mm MIP image shows course of right coronary artery within
anterior atrioventricular groove. Left anterior descending artery is shown
within anterior interventricular groove, and left circumflex artery is shown
in posterior atrioventricular groove.
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Fig. 2D —CT images of normal heart in 53-year-old man. Ao = aortic
root, CS = coronary sinus, LA = left atrium, LAD = left anterior descending
artery, LCx = left circumflex artery, LM = left main coronary artery, LV =
left ventricle, PDA = posterior descending artery, RA = right atrium, RCA =
right coronary artery, RV = right ventricle, RVOT = right ventricular outflow
tract. Axial 5-mm MIP image shows origin of posterior descending artery from
distal right coronary artery.
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Fig. 3A —Conus branch anatomy variations. Ao = aortic root, LA = left
atrium, LAD = left anterior descending artery, LM = left main coronary artery,
LV = left ventricle, RA = right atrium, RCA = right coronary artery, RVOT =
right ventricular outflow tract, SAN = sinoatrial node branch. Left anterior
oblique 5-mm maximum-intensityprojection (MIP) image shows conus branch
(arrow) in 44-year-old woman as it arises separate from right
coronary artery off of right coronary cusp.
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Fig. 3B —Conus branch anatomy variations. Ao = aortic root, LA = left
atrium, LAD = left anterior descending artery, LM = left main coronary artery,
LV = left ventricle, RA = right atrium, RCA = right coronary artery, RVOT =
right ventricular outflow tract, SAN = sinoatrial node branch. Left anterior
oblique 15-mm MIP image shows common origin of conus branch (arrow)
and right coronary artery in 40-year-old man.
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Fig. 3C —Conus branch anatomy variations. Ao = aortic root, LA = left
atrium, LAD = left anterior descending artery, LM = left main coronary artery,
LV = left ventricle, RA = right atrium, RCA = right coronary artery, RVOT =
right ventricular outflow tract, SAN = sinoatrial node branch. Axial 10-mm MIP
image shows conus branch (arrow) arising from proximal RCA in
52-year-old man. It then courses anteriorly toward right ventricular outflow
tract.
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Fig. 3D —Conus branch anatomy variations. Ao = aortic root, LA = left
atrium, LAD = left anterior descending artery, LM = left main coronary artery,
LV = left ventricle, RA = right atrium, RCA = right coronary artery, RVOT =
right ventricular outflow tract, SAN = sinoatrial node branch. Axial 10-mm MIP
image shows conus branch (arrow) arising from left anterior
descending artery in 46-year-old man.
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Fig. 4A —Sinoatrial node branch variations. Ao = aortic root, D1 =
first diagonal, GCV = great cardiac vein, LA = left atrium, LAD = left
anterior descending artery, LCx = left circumflex artery, LM = left main
coronary artery, OM1 = first obtuse marginal, RCA = right coronary artery,
RVOT = right ventricular outflow tract, SVC = superior vena cava. Axial 10-mm
maximum-intensity-projection (MIP) image in 64-year-old man shows large
sinoatrial node branch (arrow) as it arises from proximal right
coronary artery. It then courses posteriorly toward cephalad aspect of
interatrial septum (arrowheads) posterior to inflow of superior vena
cava.
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Fig. 4B —Sinoatrial node branch variations. Ao = aortic root, D1 =
first diagonal, GCV = great cardiac vein, LA = left atrium, LAD = left
anterior descending artery, LCx = left circumflex artery, LM = left main
coronary artery, OM1 = first obtuse marginal, RCA = right coronary artery,
RVOT = right ventricular outflow tract, SVC = superior vena cava. Axial 10-mm
MIP image shows sinoatrial node branch (arrow) in 65-year-old woman
as it arises from proximal left circumflex artery: Sinoatrial branch still
courses toward cephalad aspect of interatrial septum.
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Fig. 5A —Marginal branch anatomy. F = foot, LAD = left anterior
descending artery, LV = left ventricle, RCA = right coronary artery, RV =
right ventricle. Right anterior oblique 10-mm maximum-intensity-projection
(MIP) image shows large marginal branch (arrow) arising from right
coronary artery (RCA) in 40-year-old woman.
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Fig. 5B —Marginal branch anatomy. F = foot, LAD = left anterior
descending artery, LV = left ventricle, RCA = right coronary artery, RV =
right ventricle. Right anterior oblique volume-rendered image shows marginal
branch (arrow) of RCA as it courses over right ventricle in
45-year-old woman.
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Fig. 6 —Distal right coronary artery anatomy in 34-year-old man. Left
anterior oblique 20-mm maximum-intensity-projection image shows course of
entire right coronary artery. Distally, posterior descending artery and
posterior lateral branch are shown, as is atrioventricular node branch. Ao =
aortic root, AVN = atrioventricular node, IMB = inferior marginal branch, LCx
= left circumflex artery, LV = left ventricle, PDA = posterior descending
artery, PLB = posterior lateral branch, RCA = right coronary artery, RVOT =
right ventricular outflow tract.
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Fig. 7A —Distal dominant right coronary artery variation on axial
projections. CS = coronary sinus, LV = left ventricle, MCV = middle cardiac
vein, PDA = posterior descending artery, PLB = posterior lateral branch, PLV =
posterolateral vein, RA = right atrium, RCA = right coronary artery, RV =
right ventricle. Axial 10-mm maximum-intensity-projection (MIP) image in
51-year-old man shows typical tortuous course of posterior descending artery
as it arises from distal right coronary artery. Posterior descending artery
travels in inferior interventricular groove along side middle cardiac vein.
Posterior lateral branch continues along distal coronary sinus to supply
inferior wall.
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Fig. 7B —Distal dominant right coronary artery variation on axial
projections. CS = coronary sinus, LV = left ventricle, MCV = middle cardiac
vein, PDA = posterior descending artery, PLB = posterior lateral branch, PLV =
posterolateral vein, RA = right atrium, RCA = right coronary artery, RV =
right ventricle. Axial 10-mm MIP image shows dual posterior descending
arteries and dual posterior lateral branches in 44-year-old man.
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Fig. 7C —Distal dominant right coronary artery variation on axial
projections. CS = coronary sinus, LV = left ventricle, MCV = middle cardiac
vein, PDA = posterior descending artery, PLB = posterior lateral branch, PLV =
posterolateral vein, RA = right atrium, RCA = right coronary artery, RV =
right ventricle. Axial 3D volume-rendered projection image shows origin of
posterior descending artery, which still courses toward middle cardiac vein,
is higher than normal in 49-year-old woman.
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Fig. 8A —Dominant left circumflex artery and posterior descending
artery anatomy. Ao = aortic root, AVGA = atrioventricular groove artery, CS =
coronary sinus, LA = left atrium, OM = obtuse marginal, PDA = posterior
descending artery, PLB = posterior lateral branch, RA = right atrium, RCA =
right coronary artery. Left anterior oblique 10-mm
maximum-intensity-projection (MIP) images show two examples of dominant left
circumflex artery anatomy with typical small nature of right coronary artery:
one in 43-year-old woman (A) and one in 44-year-old man (B).
Atrioventricular groove artery descends as larger-caliber artery in posterior
atrioventricular groove subjacent to coronary sinus.
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Fig. 8B —Dominant left circumflex artery and posterior descending
artery anatomy. Ao = aortic root, AVGA = atrioventricular groove artery, CS =
coronary sinus, LA = left atrium, OM = obtuse marginal, PDA = posterior
descending artery, PLB = posterior lateral branch, RA = right atrium, RCA =
right coronary artery. Left anterior oblique 10-mm
maximum-intensity-projection (MIP) images show two examples of dominant left
circumflex artery anatomy with typical small nature of right coronary artery:
one in 43-year-old woman (A) and one in 44-year-old man (B).
Atrioventricular groove artery descends as larger-caliber artery in posterior
atrioventricular groove subjacent to coronary sinus.
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Fig. 8C —Dominant left circumflex artery and posterior descending
artery anatomy. Ao = aortic root, AVGA = atrioventricular groove artery, CS =
coronary sinus, LA = left atrium, OM = obtuse marginal, PDA = posterior
descending artery, PLB = posterior lateral branch, RA = right atrium, RCA =
right coronary artery. Axial 10-mm MIP image shows dual posterior descending
arteries as they arise from distal atrioventricular groove artery in
44-year-old man with dominant left circumflex artery.
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Fig. 9 —Codominance. Axial 10-mm maximum-intensity-projection image
reveals codominant anatomy in which posterior descending artery arises from
right coronary artery and posterior lateral branch arises from distal left
circumflex artery in 33-year-old man. LV = left ventricle, PDA = posterior
descending artery, PLB = posterior lateral branch, RCA = right coronary
artery, RV = right ventricle.
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Fig. 10 —Dominant left coronary artery anatomy. Left anterior oblique
schematic diagram of dominant left coronary artery anatomy, including left
anterior descending artery and left circumflex artery tributaries, is shown.
AVGA = atrioventricular groove artery, PDA = posterior descending artery.
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Fig. 11 —Left main coronary artery bifurcation. Anterior caudal 10-mm
maximum-intensity-projection image displays typical bifurcation of left main
coronary artery into left anterior descending and left circumflex arteries in
47-year-old man. AVGA = atrioventricular groove artery, D1 = first diagonal,
LAD = left anterior descending artery, LCx = left circumflex artery, LM = left
main coronary artery, OM1 = first obtuse marginal, SAN = sinoatrial node
branch.
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Fig. 12A —Ramus intermedius anatomy. LAD = left anterior descending
artery, LCx = left circumflex artery, LM = left main coronary artery, RI =
ramus intermedius artery. Right anterior oblique caudal 10-mm
maximum-intensity-projection (MIP) image displays trifurcation of left main
coronary artery into left anterior descending artery, ramus intermedius
artery, and left circumflex artery in 49-year-old man.
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Fig. 12B —Ramus intermedius anatomy. LAD = left anterior descending
artery, LCx = left circumflex artery, LM = left main coronary artery, RI =
ramus intermedius artery. Axial 10-mm MIP image shows left main coronary
artery dividing into left anterior descending artery, left circumflex artery,
and ramus intermedius branches in 42-year-old woman.
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Fig. 12C —Ramus intermedius anatomy. LAD = left anterior descending
artery, LCx = left circumflex artery, LM = left main coronary artery, RI =
ramus intermedius artery. Left posterior cranial 3D volume-rendered projection
image shows branching ramus intermedius artery, which is mostly distributed as
obtuse marginal branch to lateral wall, in 52-year-old man.
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Fig. 13 —Left anterior descending artery course. Right anterior
oblique 10-mm maximum-intensity-projection image reveals entire course of left
anterior descending artery within anterior interventricular groove in
44-year-old woman. Distally, it is seen wrapping around left ventricular apex
(arrows). LA = left atrium, LV = left ventricle.
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Fig. 14A —Myocardial bridge and septal perforator branch anatomy in
39-year-old woman. LA = left atrium, LAA = left atrial appendage, LV = left
ventricle, S1, S2, S3 = first, second, and third septal perforators. Right
anterior oblique 10-mm maximum-intensity-projection (MIP) image displays left
anterior descending artery and septal perforator branches. Myocardial bridge
overlies left anterior descending artery just beyond second septal perforator
(arrows).
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Fig. 14B —Myocardial bridge and septal perforator branch anatomy in
39-year-old woman. LA = left atrium, LAA = left atrial appendage, LV = left
ventricle, S1, S2, S3 = first, second, and third septal perforators.
Short-axis (left anterior oblique) 5-mm MIP image at level of myocardial
bridge shows left anterior descending artery (arrow) deep to right
ventricular myocardium junction with left ventricle.
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Fig. 15A —Diagonal branch anatomy. D1 = first diagonal, D2 = second
diagonal, LAD = left anterior descending artery, LCx = left circumflex artery,
LM = left main coronary artery, LV = left ventricle, RI = ramus intermedius
artery, SP = septal perforator branches. Axial caudal oblique 10-mm
maximum-intensity-projection (MIP) image reveals two diagonal branches (D1 and
D2) from left anterior descending artery in 55-year-old man. Diagonal branches
course laterally, and small septal perforator branches course medially.
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Fig. 15B —Diagonal branch anatomy. D1 = first diagonal, D2 = second
diagonal, LAD = left anterior descending artery, LCx = left circumflex artery,
LM = left main coronary artery, LV = left ventricle, RI = ramus intermedius
artery, SP = septal perforator branches. Cranial left anterior oblique 10-mm
MIP image shows left anterior descending artery and two diagonal branches in
47-year-old man.
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Fig. 16A —Nondominant left circumflex artery anatomy in 36-year-old
man. AVGA = atrioventricular groove artery, CS = coronary sinus, D1 = first
diagonal, GCV = great cardiac vein, LAD = left anterior descending artery, LCx
= left circumflex artery, OM1 = first obtuse marginal. Axial 10-mm
maximum-intensity-projection (MIP) image shows left circumflex artery and left
anterior descending artery with large first obtuse marginal arising from
proximal left circumflex artery. Small left circumflex artery descends in
posterior atrioventricular groove as atrioventricular groove artery.
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Fig. 16B —Nondominant left circumflex artery anatomy in 36-year-old
man. AVGA = atrioventricular groove artery, CS = coronary sinus, D1 = first
diagonal, GCV = great cardiac vein, LAD = left anterior descending artery, LCx
= left circumflex artery, OM1 = first obtuse marginal. Left anterior oblique
10-mm MIP image displays left circumflex artery anatomy with its descent as
atrioventricular groove artery.
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Fig. 17A —Dominant left circumflex artery anatomy in 44-year-old man.
AVGA = atrioventricular groove artery, LCx = left circumflex artery, LM = left
main coronary artery, OM1 = first obtuse marginal, OM2 = second obtuse
marginal, PDA = posterior descending artery, PLB = posterior lateral branch,
RI = ramus intermedius artery. Left anterior oblique cranial 3D
volume-rendered image shows dominant left circumflex artery anatomy with two
obtuse marginal branches.
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Fig. 17B —Dominant left circumflex artery anatomy in 44-year-old man.
AVGA = atrioventricular groove artery, LCx = left circumflex artery, LM = left
main coronary artery, OM1 = first obtuse marginal, OM2 = second obtuse
marginal, PDA = posterior descending artery, PLB = posterior lateral branch,
RI = ramus intermedius artery. Axial 3D volume-rendered image reveals dual
posterior descending artery and posterior lateral branch arising from distal
atrioventricular groove artery.
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Fig. 18A —Anomalous origin of right coronary artery and left main
coronary artery. Ao = aortic root, LAD = left anterior descending artery, LM =
left main coronary artery, RCA = right coronary artery, RVOT = right
ventricular outflow tract. Axial 5-mm maximum-intensity-projection (MIP) image
shows anomalous origin of right coronary artery in 43-year-old woman from
anterior proximal ascending aorta with subsequent acute rightward course
before reaching anterior atrioventricular groove.
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Fig. 18B —Anomalous origin of right coronary artery and left main
coronary artery. Ao = aortic root, LAD = left anterior descending artery, LM =
left main coronary artery, RCA = right coronary artery, RVOT = right
ventricular outflow tract. Three-dimensional volume-rendered projection image
shows anomalous right coronary artery in same patient as A above level
of right coronary cusp (arrow).
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Fig. 18C —Anomalous origin of right coronary artery and left main
coronary artery. Ao = aortic root, LAD = left anterior descending artery, LM =
left main coronary artery, RCA = right coronary artery, RVOT = right
ventricular outflow tract. Axial 10-mm MIP image reveals anomalous origin of
left main coronary artery in 35-year-old man from right cusp near origin of
right coronary artery. It then takes intraseptal course posterior to right
ventricular outflow tract near cephalad aspect of interventricular septum.
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Subjects and Methods
Coronary CTA protocols usually image the heart using cranial-to-caudal
acquisition [3]. However,
caudal-to-cranial scanning acquisitions are implemented when concomitant
imaging of the pulmonary arteries is desired in patients with atypical chest
pain [4]. We describe both of
these protocols because the cardiac venous anatomy may be displayed with
variation in enhancement depending on the type of data acquisition.
The patients who participated in our study were imaged after the
institutional review board had approved the study, which complies with the
Health Insurance Portability and Accountability Act, and after they had
provided written informed consent. Patients were recruited from October 2004
to June 2005.
Imaging was performed on a 64-slice (32-detector) MDCT scanner (Sensation
Cardiac 64, Siemens Medical Solutions) after the patient was premedicated with
oral atenolol (50–100 mg), IV metoprolol (5- to 10-mg boluses, up to 50
mg), or both. An upper extremity 20-gauge IV catheter was used for venous
access. Sublingual nitroglycerin (0.4 mg) was provided to induce coronary
vasodilatation. Bolus timing was measured in the mid ascending aorta with 20
mL of iodixanol (320 mgI/mL [Visipaque, GE Healthcare]) administered at a rate
of 5 mL/s followed by a 50-mL saline flush, also administered at a rate of 5
mL/s). Alternatively, bolus tracking can be used to trigger data acquisition
by placing a region of interest over the mid ascending aorta and setting the
trigger threshold to 160 H above baseline.
Single-sector reconstructions of the coronary arteries were performed at
65% and 35% of the R-R length and were then modified to a different phase
start if there were motion artifacts. Reconstructions were performed on a
workstation (Wizard, Siemens Medical Solutions) and then transferred to
another workstation (TeraRecon, TeraRecon) for MPRs and MIPs.
Cases were selected to show the normal coronary arterial and venous
anatomy. MIPs were obtained using various thicknesses (5–30 mm) and were
displayed using standard orientations (right anterior oblique, left anterior
oblique, axial) with or without caudal or cranial angulation. Volume-rendered
images were also obtained using various orientations.
Cranial-to-Caudal Acquisition
Coronary CTA was performed 5 seconds after aortic peak density; 100 mL of
iodixanol (Visipaque) was administered at 5 mL/s and was followed by a 50-mL
saline flush at 5 mL/s [3].
Retrospective ECG-gating was used with the following parameters: collimation,
0.6 mm; tube rotation time, 0.33 seconds; tube voltage, 120 mV; effective mAs,
750–850; pitch, 0.2; and scanning time, 10–12 seconds.
Scanning coverage was from the level of the carina to the bottom of the
heart. Reconstruction field of view, slice thickness and reconstruction
increment, and smooth kernel were as follows: 15–22 cm; 0.6 and 0.3 mm,
respectively; and B25f. ECG pulsing is usually implemented for tube current
modulation and is needed to reduce radiation exposure
[5].
Caudal-to-Cranial Acquisition
For the caudal-to-cranial acquisition, a patient preparation and scanning
protocol similar to that described in the previous section was used. However,
contrast injection was performed with a higher volume of contrast material
using a biphasic protocol: 100 mL of iodixanol was administered at 5 mL/s
followed by 30 mL of iodixanol at 3.0 mL/s and then a 50-mL saline flush at 3
mL/s. The additional volume of contrast material resulted in a prolonged time
for contrast injection to ensure adequate enhancement of the pulmonary
arteries [4]. As a result,
streak artifacts arising from the superior vena cava and right atrium were
present in 37 (88%) of 42 studies; however, these artifacts interfered with
the visualization of the right coronary artery (RCA) in only one (2.4%) of the
42 cases [4].
The thorax from the lung bases to just above (1–2 cm) the aortic arch
was scanned with a 12- to 15-second acquisition (no ECG pulsing), but scanning
can include the entire thorax when ECG pulsing is applied. As with
cranial-to-caudal acquisitions, ECG pulsing is needed to reduce radiation
exposure [5]. Reconstruction
field of view, slice thickness and reconstruction increment, and kernel for
the coronary arteries were similar to those for the cranial-to-caudal
acquisition. However, reconstructions were also obtained with a larger field
of view [4] to display the
pulmonary arteries, thoracic aorta, lungs, and thoracic soft tissues.
Normal Anatomy of the Coronary Arteries
The right and left coronary arteries originate from the right and left
sinuses of Valsalva of the aortic root, respectively. The posterior sinus
rarely gives rise to a coronary artery and is referred to as the
"noncoronary sinus." The locations of the sinuses are anatomic
misnomers: The right sinus is actually anterior in location and the left sinus
is posterior. The myocardial distribution of the coronary arteries is somewhat
variable, but the right coronary artery (RCA) almost always supplies the right
ventricle (RV), and the left coronary artery (LCA) supplies the anterior
portion of the ventricular septum and anterior wall of the left ventricle
(LV). The vessels that supply the remainder of the LV vary depending on the
coronary dominance, which we explain later.
RCA Anatomy
The RCA arises from the right coronary sinus somewhat inferior to the
origin of the LCA. After its origin from the aorta, the RCA passes to the
right of and posterior to the pulmonary artery and then emerges from under the
right atrial appendage to travel in the anterior (right) atrioventricular (AV)
groove (Figs. 1 and
2A,
2B,
2C,
2D). In about half of the
cases, the conus branch is the first branch of the RCA (Fig.
3A,
3B,
3C,
3D). In the other half, the
conus branch has an origin that is separate from the aorta. The conus branch
always courses anteriorly to supply the pulmonary outflow tract. Occasionally,
the conus branch can be a branch of the LCA
(Fig. 3D), have a common origin
with the RCA, or have dual or multiple branches.
In 55% of cases, the sinoatrial nodal artery (Figs.
3C,
3D, and
4A) is the next branch of the
RCA, arising within a few millimeters of the RCA origin. In the remaining 45%
of cases, the sinoatrial nodal artery arises from the proximal left circumflex
(LCx) artery (Figs. 4B and
11). In either case, the
sinoatrial nodal artery always courses toward the superior vena cava inflow
near the cephalad aspect of the interatrial septum. As the RCA travels within
the anterior AV groove, it courses downward toward the posterior (inferior)
interventricular septum. As it does this, the RCA gives off branches that
supply the RV myocardium; these branches are called "RV marginals"
or "acute marginals" (Fig.
5A,
5B). They supply the RV
anterior wall. After it gives off the RV marginals, the RCA continues around
the perimeter of the right heart in the anterior AV groove and courses toward
the diaphragmatic aspect of the heart.
Coronary Dominance
The artery that supplies the posterior descending artery (PDA) and the
posterolateral branch determines the coronary dominance. If the PDA and PLB
arise from the RCA, then the system is said to be right dominant (80–85%
of cases) (Figs. 6 and
7A,
7B,
7C). In this instance, the RCA
supplies the inferoseptal and inferior segments of the LV
[6]. If the PDA and PLB arise
from the LCx artery, then the system is said to be left dominant (15–20%
of cases) (Figs. 8A,
8B,
8C and
17A,
17B). In this instance, the
LCA supplies the inferoseptal and inferior segments of the LV. If the PDA
comes from the RCA and the PLB comes from the LCx artery, the system is
codominant (about 5% of cases) (Fig.
9).
In left-dominant and codominant systems, the LCx artery continues in the
posterior AV groove as the left AV groove artery and gives rise to left PLB.
In left dominance, the PDA is the final branch of the AV groove artery. The
distal RCA divides into the PDA and PLB in a right-dominant system. The
nondominant system is usually noticeably smaller in caliber than the dominant
system. This difference in caliber can be used as an additional clue to
determine whether the coronary anatomy is right or left dominant. Usually
arising just distal to the origin of the PDA, the AV nodal artery
(Fig. 6) can be recognized by
its direct vertical course off of the distal RCA. In cases of left dominance,
the AV node branch has a similar appearance and location, but it arises just
proximal to the (left) PDA.
LCA Anatomy
The LCA normally emerges from the left coronary sinus as the left main (LM)
coronary artery (Fig. 10). The
LM coronary artery is short (5–10 mm), passes to the left of and
posterior to the pulmonary trunk, and bifurcates into the left anterior
descending (LAD) and LCx arteries (Fig.
11). Occasionally, the LM coronary artery trifurcates into the LAD
artery, the LCx artery, and the ramus intermedius artery (Fig.
12A,
12B,
12C).
Ramus Intermedius Artery
The most common variation in LCA anatomy is the presence of a trifurcation
of the LM coronary artery. In this instance, the LM coronary artery
trifurcates into the LAD artery, LCx arteries, and an artery between them
called the "ramus intermedius" artery (Fig.
12A,
12B,
12C). The ramus intermedius
artery itself has variable branching. The ramus intermedius can be distributed
as a diagonal branch or as an obtuse marginal branch depending on whether it
supplies the anterior or the lateral wall, respectively.
LAD Artery
The LAD artery (Fig. 13)
runs in the anterior interventricular sulcus along the ventricular septum.
Commonly, the LAD artery may be embedded within the anterior myocardium
forming an overlying myocardial bridge (Fig.
14A,
14B). Myocardial bridging is
seen more often on CT than described in the coronary angiography literature.
Most myocardial bridges are asymptomatic, although rarely myocardial bridging
can be associated with ischemia. The LAD artery has branches called
"septal perforators" (Fig.
14A,
14B) that supply the anterior
ventricular septum. It also has diagonal arteries (Fig.
15A,
15B) that course over and
supply the anterior wall of the LV. The diagonals and septal perforators are
numbered sequentially from proximal to distal (i.e., D1, D2, S1, S2).
LCx Artery
The LCx artery (Figs. 16A,
16B,
17A,
17B, and
2A,
2B,
2C,
2D,
4B,
8A,
8B,
8C,
11,
12A,
12B,
12C,
15A,
15B) runs in the posterior AV
groove analogous to the course of the RCA on the opposite side. The major
branches of the LCx artery consist of obtuse marginals (OMs) (Figs.
16A,
16B and
17A,
17B). OM branches supply the
lateral wall of the LV. They are numbered sequentially from proximal to distal
(i.e., OM1, OM2, OM3).
Anomalies of RCA Origin
The RCA can have an anomalous origin. It is important to be aware of this
possibility to avoid misinterpreting coronary CTA. Typically, the anomalous
origin of the RCA is from the left coronary sinus of Valsalva, with a
subsequent course between the aortic root and right ventricular outflow tract.
Depiction of these anomalies is beyond the scope of this article; however,
this and other anomalies of RCA origin are described by Kim et al.
[7]. An example of an anomalous
origin of the RCA is shown in Figure
18A,
18B,
18C.
Anomalies of LCA Origin
The LCA and its branches can have an anomalous origin. It is important to
be aware of this possibility to avoid misinterpreting coronary CTA. Some of
these anomalies are associated with an increased risk of sudden death or
cardiac arrest (Fig. 18C).
Depiction of these anomalies is beyond the scope of this article; however,
anomalies of LM, LAD, and LCx origin are reviewed by Kim et al.
[7].
Coronary Venous Anatomy
The great cardiac vein (Figs.
4B and
16A) is located in the
anterior interventricular sulcus, alongside the LAD artery. It courses upward
from the apex and drains into the coronary sinus. The middle cardiac vein
(Figs. 7A and
7C) also begins at the apex,
but it courses upward in the inferior interventricular sulcus, alongside the
PDA. Between the two, there is a variable posterolateral vein
(Fig. 7C) draining the lateral
wall of the LV. The coronary sinus (Figs.
7A,
7C,
16A, and
16B) is the wide vein that
courses in the posterior AV groove accompanying the LCx artery and the AV
groove artery. It drains into the right atrium and receives the great cardiac
vein proximally and the middle cardiac vein distally.
Reporting System of Coronary Artery Disease
In an attempt to standardize the reporting of coronary artery disease, an
ad hoc committee of the American Heart Association developed nomenclature and
further divided the main coronary arteries into proximal, middle, and distal
segments [8].
The proximal RCA segment is from the ostium to one half the distance to the
acute margin of the heart. The middle RCA segment is the RCA from the end of
the above segment to the acute margin of heart. The distal RCA segment is the
RCA running along the right AV groove from the acute margin to the origin of
the PDA.
The LAD proximal segment is proximal to and includes the origin of the
first major septal perforator. The middle LAD segment is the LAD artery
immediately distal to the origin of the first major septal perforator that
extends to the point where the LAD artery forms an angle (right anterior
oblique view). This angle is often, but not always, close to the origin of the
second diagonal. If this angle or diagonal is not identifiable, this segment
ends one half the distance from the first major septal perforator to the apex.
The apical LAD segment is the terminal portion of the LAD artery that begins
at the end of the previous segment and extends to or beyond the apex.
The proximal LCx segment is the mainstem of the LCx artery from its origin
off the LCA to and including the origin of an obtuse marginal. The distal LCx
segment is the LCx artery distal to the origin of the obtuse marginal and
travels along or close to the posterior AV groove.
Conclusion
Coronary CTA is emerging as an essential imaging tool for evaluating the
coronary arteries. Knowledge of the CT appearance of the coronary anatomy and
various coronary artery anomalies is essential for accurate diagnosis and
proper patient treatment.
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Abstract
Introduction
