Cardiac Anatomy for Radiology
Frandics Chan, MD, PhD.
Stanford University Medical Center
Department of Radiology
August 22, 2002
INTRODUCTION
Radiological diagnosis of cardiac disease, like diseases of any other organ system, begins with a
firm understanding of the normal anatomy of the heart. But unlike other organs, the heart is
intrinsically dynamic, constantly in motion, supporting life by pumping blood that provides
oxygen and nutrients to every cell in our bodies. Thus, an understanding of the normal heart
must also include cardiac motion and hemodynamics of the resultant blood flow. In this
discussion, we will concentrate on structural anatomy. Dynamic behaviors, such as wall motion,
pressure and flow, will be deferred to another lecture. Anatomy of the heart can be broken down
into five components; the great cardiac vessels, the pericardium, the cardiac chambers, the heart
valves, and the coronary vessels.
CARDIAC GREAT VESSELS
The heart is situated within the mediastinum, between the left and right lungs. According to
traditional division of the mediastinum devised by anatomists, the heart falls within the middle
mediastinum beneath the superior mediastinal compartment. Radiologists, lead by Benjamin
Felson [1], place the heart in the anterior mediastinum, as judged by the lateral view of the chest
radiograph. The rationale for this classification is that a lesion in the anterior mediastinum is
indistinguishable from a lesion of the heart based on chest radiography. Today, this ambiguity is
routinely resolved with tomographic imaging, such as computed tomography or magnetic
resonance imaging. Therefore, the nomenclature becomes a matter of tradition.
When a thoracic surgeon explores the heart, he first performs a stenotomy by a midline resection
of the sternum, revealing the outer surface of the parietal pericardium. After stripping of the
pericardium, the cardiac great vessels and the anterior surface heart are exposed. The right
atrium receives its systemic venous return near the superior vena cava superiorly, and inferior
vena cava inferiorly. In the plane of the cardia skeleton, which contains the four heart valves, the
aortic root originates near the middle while the pulmonary trunk originates anterior and to the
left of the aorta. The ascending aorta and the pulmonary trunk twist around each artery by
180 degrees, as a result of the twisting, divisions by the aorticopulmonary septum during
the embryological truncus arteriosus. The pulmonary trunk is shorted and the ascending aorta
such that when it divides into the right and left pulmonary artery, the right pulmonary artery path
is underneath the aortic arch to reach the right lung. It normally reveals trouble and anterior to
and slightly beneath the right main stem bronchus. This relationship is set to be epiarterial,
meaning the bronchus is above the right pulmonary artery. After the bifurcation, the left
pulmonary artery troubles posteriorly, and reaches over the left main stem bronchus before its
bifurcations to the left upper lobe bronchus. This relationship is set to be hyparterial, meaning
the left main stem bronchus is beneath the left pulmonary artery. These are critical relationships
that determine the sidedness of the chest. Their correct interpretation determines the chest’s situs
solitus “normal”, situs reversus, and situs ambiguous.
The aorta immediately gives off normally to coronary arteries; the left main artery and the right
coronary artery. The next major branch originates at the aortic arch namely the right brachial
cephalic artery, followed by the left carotid artery, and the left subclavian artery. The left atrium
receives pulmonary venous drainage through normally four pulmonary veins that enter the left
atrium posteriorly. They are respectively named left and right superior and inferior pulmonary
veins. However, these vessels could merge separately before they enter the left atrium, and the
number of vessels entering the left atrium proper may vary between one and four. Regardless of
the anatomic variation, the pulmonary veins must drain all regions of the lungs into the left
atrium alone.
The blood supply to the mylecardium of the heart is collected via the coronary venous system.
The majority of the venous return is drained through the coronary sinus which empties into the
right atriums as medial to the entrance of the inferior vena cava. This position is very close to
the atroseptum. In one type of congenital abnormality, this close relationship permits an abrance
communication between the coronary sinus and the left atrium, creating a right to left shunt.
RADIOGRAPHIC CORRELATION
The soft tissue of the cardiovascular structure within the mediastinum, and the blood contained
within it essentially create only one radiographic density. Therefore, without injecting the
contrast material, it is impossible to distinguish separate lumens of the great vessels or the
individual chambers of the heart. The interface of the cardiovascular system with the adjacent
lung, create an interface that permits visualization. Therefore, by inspecting the
cardiomediastinal silhouettes on the chest radiographs it is possible to infer the likely underlying
structure that creates it, using knowledge from anatomy. Traditionally, a cardiac series consists
of four views of the chest. They are the extended PA and lateral projections of the chest, plus a
30 LAO view, and a 60 RAO view. To help better visualize the posterior cardiac contour, it is
customary to administer barium swallowed during the exposure for the lateral, PA, and the RAO
projections. Given today’s advances in tomographic imaging and accessibility of
echocardiography, the extended cardiac series is rarely performed. However, its discussion still
serves a useful beginning point for the different relationship of the cardiovascular structure
within the chest.
The frontal chest radiograph, the left cardiomediastinal silhouettes beginning from the top to the
bottom represent the aortic arch, the left pulmonary artery, the left atrial appendage, and the left
ventricle. The take off of the left pulmonary artery is considered the left hilum.
On the right cardiamediastinal border, looking from the top to the bottom, the silhouette
represents the right brachial cephalic vein, a straight superior vena cava that drains in to the right
atrium. The SVC is further divided into an upper and lower portion by the azygus vein. In
normal anatomy, the azygus vein can be seen as an elliptic density above the left mainstem
bronchus and adjacent to the trachea. The right pulmonary artery truffled behind the SVC and
forms the right hilum. For most people the right hilum is inferior to the left hilum.
On the lateral chest radiograph, the retrosternal representing a direct apposition of the left and
right lung at the interior junction line. The interior border of the heart represents the right
ventricle. On some patients, superior to the right ventricle border the ascending aorta can be
seen. At the posterior border of the heart, where it merges with the diaphragm, it can usually be
seen as a short strict segment that represents the supradiaphragmatic portion of the inferior vena
cava. The curvature that represents the left ventricle is usually situated just interior to this IVC
silhouette. If the left inticular(?) convexity is substantially displaced posterior to the IVC, left
ventricular enlargement may be suspected. Above the IVC and left ventricular silhouette lies the
left atrium. The pulmonary veins that enter the left atrium can sometimes be seen en face
creating a larger like density. It has a characteristic location, and should not be confused with a
lung nodule. Depending on the contents of fance(?) within the AP window, the pulmonary trunk
and the left pulmonary artery sometimes can be seen beneath the aortic arch. If barium
swallowed was administered, three interior indentations are normally identified, representing the
crossing of the esophagus to the aortic arch, the left main stem bronchus and the left atrium.
The 30 left anterior oblique view attends to view the ventricular septum at on such that the right
ventricle aligns to the right and the left ventricle aligns to the left. In this view, the transverse
diameter of the heart is at its shortest. The left cardiamediastinal contour represents the aortic
arch and descending aorta, the left atrium and the left ventricle. The right cardiamediastinal
border represents the superior vena cava, the right atrium, and the right ventricle.
In the 60 right anterior oblique view, the ventricles are aligned at their long axes such that the
apex lies to the extreme left, while the base of the heart lies to the right. In this view, the left and
right ventricles super pose on each other and most of the heart valves are seen etch on. This
view also shows the transverse diameter of the cardiac silhouette at its largest. The left
cardiamediastinal silhouette represents a popdown of the aortic arch, the pulmonary trunk, the
pulmonary on filed track(?), and the ventricular septum. The right cardiamediastinal silhouette is
usually obscured by the retepal(?) column. If barium swallow wasn’t administered indentation
by the aortic arch, the left mainstem bronchus and the left atrium can again be seen.
PERICARDIUM
The pericardium is composed of two layers. The parietal pericardium is a fibrous membrane that
immediately aposed the parietal pleura. The visceral pericardium is adhered to the epicardia and
normally cannot be separate from the heart. Between the visceral and the parietal pericardium
we site a small multi epicardia fluid that serves as lubrication as the heart moves within the fixed
mediastinum. The parietal pericardium is in general three from the surface of the heart except
where the great cardiac vessels pierce through the pericardium. The foats(?) of the parietal
pericardium around these excess of the great vessels form borders where pericardial contents can
go. There are two important potential spaces. The oblique sinus is the potential space along the
posterior border of the heart beneath the origin of the pulmonary veins. A smaller transverse
sinus exists above the entrance of the pulmonary veins. This space has a complex geometry. On
the left, it is limited by the pulmonary trunk as it bifurcates. On the right it is limited by the
superior vena cava. However, in between these two there is a finger like recess that extends
superiorly behind the ascending aorta. There can be a small amount of fluid collection within
this space known as the superior recess of the transverse sinus. This could be seen on axial
images of CT. It has a characteristic location, a crescentic shape, and a flute density. It should
not be confused with a mediastinal node.
The parietal pericardium is enveloped by epicardia thet(?) the inferior portions of the
pericardium is tightly adhered to the diaphragm. It envelops the heart and a proximal portion of
the great cardiac vessels. Superiorly, the pericardium envelops and terminates at the aortic arch.
CARDIAC CHAMBER: RIGHT ATRIUM
Interior of the right atrium consists of a smooth wall posterior portion and atrepeculated(?)
anterior lateral portion. These two morphologically different regions meet at a vertical tubular
ridge that extends from the anderal(?) lateral margin of the SVC all the way to the anderal lateral
margin of the interior vena cava. This ridge is called crisda terminalis. On some individuals,
this ridge can be very prominent, to the point of creating a mass appearance. However, its
characteristics shape and location distinguish this benign structure from a cardiac tumor.
At the entrance of the interior cava lies a thin baffle of tissue, called the Eustachian valve.
Although termed as a valve, it is not a functional valve that opens or closes the orifice of the
IVC. In Utero, the eustachian valve serves to redirect the oxygen rich blood that returns from the
IVC into the foraman ovale, which is then distributed by the lapsire(?) heart to the systemic
arteries. At birth, the foraman ovale is closed and the oxygen pours blood from the systemic
venous returned is directed to the lungs through the right ventricle. Thus, the gestation valve no
longer serves a function. Between the IVC and the adroseptum(?) lies the orfus(?) of the
coronary sinus. Its origin too is guarded by a smaller baffle, termed Thebesian valve. In some
individuals, this valve can be prominent such that it guards the entrance of the coronary sinus. It
can make the engagement of the coronary sinus by cardiac interventionist difficult. Above the
gestation valve at the septal wall lies the remanence of the foraman ovale. In the majority of the
population, the foraman ovale is anatomically sealed. However, in 10-20% of the population, the
membrane guarding the foraman ovale can be opened forcefully by catheter or a probe. It is kept
closed by the virtue of a higher left pressure than the right. The superior vena cava enters the
right atrium superiorly. Between the orphus(?) of the SVC and the foraman ovale lies the
sinoatrial node. This is the origin of the cardiac electro pacing. However, its location is not
visible radiographically.
Anterior to the entrance of the SVC lies the right atria appendage. Its appearance differs from
the left atria appendage. In fact, the differences are the principle characteristics that differentiate
the morphological right and left atria. The right atria appendage is said to be larger, broad based,
pyramidal in shape. Finally, blood in the right atrium enters the right ventricle via the tricuspid
valve. The exception is the cardiac chamber; right ventricle.
The right ventricle is a V shaped chamber consisting of three parts: the edmans(?), the body and
the outflow track. The outflow track is separate from the body of the ventricle by a ridge of
tissue roughly horizontal in position at the superior margin of the muscular septum. This ridge
of tissue is called crista ventricularis. Below the crista ventricularis, the right ventricular wall is
coarsely trabeculated. Above the crista ventricularis is a cone shaped muscular tissue that is
contractile, called conal(?) tissue. Within the conal(?) tissue is aluminous base referred to as the
infundibulum, meaning funnel. The apex of the conal(?) tissue resides in the pulmonary valve.
The morphologic right ventricle differs from the left ventricle in three important aspects. First,
compared with the left ventricle, the right ventricular wall is more coarsely trabeculated.
Second, there is a problem in the muscular bridge that joins the septal wall with the interior right
ventricular wall near the apex. This bridge is called the moderator bend. It contains conducting
fiber that permits early depolarization of the lateral wall. Third, unlike the aortic and the
mygal(?) valve, the pulmonary valve and the tricuspid valve are widely separated. This
separation permits a complete muscular ring surrounding the right ventricular ofotrack(?). This
muscular ring is absent in the left ventricular ofotrack(?).
The chordae tendineae of the tricuspid valve inserts to a number of small papillary muscles. In
addition, they may insert directly onto the septal wall. This feature is absent in the ? valve of the
left ventricle.
CARDIAC CHAMBERS: LEFT ATRIUM
The left atrium is characterized by one to four entries for the pulmonary veins. The foraman
ovale can be seen at the septal wall. It persists a left atrial appendage that differ from the right
side in its smaller dimension, narrow base, tubular in shape, and corregated in contour. In
relative, the normal heart, the distinguishing features of their appendages are usually enough to
tell the two atria apart. However, in complex congenital disease that have under gone significant
remodeling of the atria or surgical alteration, differentiating the two atria can be difficult. In
practice, we take advantage of the fact that when there is a single supra hepatic IVC, it nearly
always drains into the morphologic right atrium. However, application in this root can be
difficult in situations where there is abdominal situs ambiguous where different branches of the
hepatic vein may drain into different atrial chambers. In these situations, we simply label the
atria as ambiguous.
CARDIAC CHAMBERS: LEFT VENTRICLE
The left ventricle receives its blood from the left atrium through the mitral valve. The chordate
tendinaea of the two mitral valve leaflets are divided and attached to two papillary mussels:
posteromodial(?) papillary mussel, and anterolateral papillary mussel. Unlike the tricuspid
valve, there is no chordate tendinaea attachment from the mitral valve to the septum.
The imnet(?) and the outflow track of the left ventricle shares a common space and the aortic
valve is directly contiguous with the mitral valve. Specifically, the noncoronary cusp of the
aortic valve is in intimate contact with the interior leaflets of the mitral valve. Compared with
the right ventricle, speculation in the left ventricle is relatively small and the wall is smooth.
This feature is the outcome of ambiological(?) process known as compaction of the left
ventricular mile cardial fiber, presumably permitting increased deficiency in its contractile
function.
HEART VALVES
The diameter of the imnet(?) valves are generally larger than the outflow valves. The larger
cross sectional area is needed to reduce flow resistance and enhance diastolic filling of the
ventricle when the atrial ventricular pressure is low relative to the systolic pressure that drives
across the outflow valves. For the imnet(?) valve to work properly and efficiently, it involves
more than the opening and the closing of the valve of the leaflets. The entire apparatus including
the leaflets, the emulous, the chordate tendinae, and the papillary muscle must work together as a
unit. Therefore functionally we have referred to the mitro apparatus and the tricuspid apparatus.
The centers of the four heart valves lie roughly on the same plane. Their physical dimensions
and integrity are maintained by the cardiac skeleton, which is a fibrocartilagenous structure that
gives physical rigidity to annuli of the valves. The cardiac skeleton also serves as an electrical
insulator between the atria and the ventricles, such that electricity is conducted only through the
atria ventricular node. On the plane of the cardiac skeleton, the aortic valve is central in location.
Relative to the aortic valve, the mitral valve is located to the left, inferiorly and posteriorly. The
tricuspid valve is located inferiorly and to the right. The pulmonary valve is located superiorly
and anteriorly. Because the aorta and the right ventricular outflow track has a spiraled
relationship, the pulmonary valve and the aortic valves are nearly at a 90 difference in
orientation. In the meanwhile, the mitral valve and the tricuspid valve are roughly coplanar.
The mitral valve named after the two cusps of a bishop’s hat, consists of a larger anterior leaflet
that is elliptical in shape, and a smaller, but broadly attached posterior leaflet that is crescentic in
shape. The tricuspid valve consists of three leaflets, labeled as septal, anterior and posterior.
The septal leaflet of the tricuspid valve is in close proximity to the anterior leaflet of the mitral
valve. In the terminology used by cardiologists, the three cusps of the aortic valves are labeled
the right coronary cusp near which the right coronary artery originates; the left coronary cups
near which the left main coronary artery originates, and the noncoronary cusp. The noncoronary
cusp is posteriorly located and is close proximity to the anterior leaflet of the mitral valve. The
right coronary cusp is most anteriorly located. The three cusps of the pulmonary valves are
labeled by their anatomical location; right cusp, left cusp and anterior cusp.
Of the four heart valves, the pulmonary valve is the most superiorly located while the tricuspid
valve is the most inferiorly located. In most clinical situations it is the aortic and or the mitral
valves that are compromised and replaced. The type of valve replaced by anatomic prosthesis
can be identified by its location, size, and orientation. In general, the prosthetic mitral valve is
larger than the aortic valve and it situates more inferiorly and to the left. On frontal projection,
the aortic valve tends to be seen on tengence(?) while the mitral valve is seen en face. On the
lateral view, the mitral valve tends to conduct flow which is tropoperpendicular(?) to the plane of
the emulous from supero posterior to infero anterior direction. The aortic valve conducts flow
from inferior to superior direction.
Compared with the mitral valve, the tricuspid valve is slightly displaced toward the apex. In
adults, if this displacement is less than 2 cm, it is considered normal. However, if the anterior
displacement of the tricuspid valve is exaggerated, this represents atrialization(?) of the right
ventricle and it is part of the ebstein normally. Because of the normal displacement of the
tricuspid valve septal leaflets relative to the anterior leaflet of the mitral valve, a fistula can be
created to communicate between the left ventricle and the right atrium. This is considered part
of the endocardiocushion(?) defect and can characterize as both a ventricular septal defect and an
atroseptal(?) defect. The converse communication between the right ventricle and the left atrium
is impossible.
ECHOCARDIOGRAPHY PLANES
The widespread availability, the economy and the efficiency of echocardiography in the
diagnosis of cardiac disease had revolutionized the practice of cardiology. As an ultrasound
application, echocardiography is likewise limited by the available sonographic window for the
visualization of the heart. The American College of Echocardiography has standardized a
number of planes for its visualizations of the heart. Because MRI and CT advance evaluations of
the heart usually follow initial investigations with echocardiography, it is often necessary to
obtain echocardiographic equivalent planes for comparison. These planes are divided into short
axis and long axis planes. The short axis views lay out the circular left ventricular wall. And at
level of the cardiac skeleton, it lays out the four valves. There are three echocardiographic law
axis; horizontal law axis, vertical law access or three chamber view, and two chamber view. The
orientation of the law axis is best understood by joined perpendicular planes to the short axis
view at the cardiac skeleton. Here the center of the mitral valve and the apex of the left ventricle
form the central access where all three long axis planes intersect. For the horizontal long axis,
this plane also cuts through the center of the tricuspid valve. In this view the left and right atria
and the left and right ventricle are seen separated by the tricuspid and mitral valves. The vertical
long axis or three chamber view can be obtained by cutting the plane through the aortic valve. In
this view one can see the left atrium separated from the left ventricle by the mitral valve and at
the same time the aortic root is seen connected through the left ventricle through the aortic valve.
Usually a small area of the right ventricle can be seen anteriorly in this view. The separation
between the three chamber view and the horizontal long axis view is usually 60. This leads a
wall to the large gap which can be filled with an additional plane called the two chamber view.
In this view, the left atrium can be seen connected with the left ventricle through the mitral
valve. The three long axis views are roughly 60 apart from one another. The milecardium(?)
visualized by each of the long axis view represents a different longitudinal portion of the left
ventricular milecardium(?). These six segments are given names septal, anterior, anterolateral,
posterior and inferior walls. In the horizontal long axis view, the septal and the lateral walls are
visualized. In the vertical long axis of the three chamber view, the anterior and the posterior
walls are visualized. In the two chamber view, the interal(?) lateral and the inferior walls are
visualized. In addition, a horizontal long axis plane nearly parallel to the four chamber view but
more superiorly located and includes the left ventricular outflow and the aortic valve. This view
is called the five chamber view.
CORONARY VESSELS
Coronary artery disease is by far the most common cardiac disease. In ?developed countries
coronary artery disease has caused more deaths than any other disease. Currently the gold
standard for the evaluations are catheter based angiography. In this procedure, separate catheters
are used to engage the left main coronary ostium and the right main coronary artery ostium. At
least two projections in the left anterior oblique, and the right anterior oblique with variable
cranial caudle angulations are taken for a complete evaluation of the coronary arteries.
In stent coronary art anatomy, the left main coronary artery originates near the left coronary cusp
of the aortic valve. It quickly bifurcates in to a left anterior descending branch and a left
circumflex branch. The left anterior descending branch travels along the anterior surface of the
ventricular septum, reaching the apex and sometimes reaching the inferior apical wall. The left
anterior descending artery transmits side branches to the left to supply the anterior and interal(?)
lateral wall. These side branches are labeled diagonal artery number one two and three
depending on their order of origins from the left anterior descending artery. A distinguishing
feature of the left anterior descending artery is that it also transmits septal perforator branches
into the septum. Thus, on angiography especially in the RAO view, the left anterior descending
artery with its perforator branches has the appearance of a comb. This feature is absent from the
diagonal branches.
The left circumflex artery travels along the left atrial ventricular groove and transmits branches
to supply the lateral and posterior wall of the left ventricle. These branches are labeled obtuse
marginal branch number one two or three dependant upon their order of origin. It should be
noted that sometime a diagonal or an obtuse marginal branch originates very close to the
bifurcation of the left main coronary artery. When this branch is within 1 cm from the
bifurcation of the left main, it is called the ramus medianus.
The right coronary artery originates near the right coronary cusp of the aortic valve and it travels
along the right atroventricular(?) groove to the inferior surface of the heart. Along the right
ventricular wall it transmits branches called acute marginal branches which are also number one
two three depending their order of origin. In greater than 75% of the population, the right
coronary will cross the inferior portion of the septum into the inferior wall of the left ventricle.
At the crossing of the atroventricular(?) groove and the inferior septum is a landmark called the
crux. At this location, the right coronary artery typically takes on an inverted U shape, near this
region, the right coronary artery transmits a branch of the (couldn’t understand word) the inferior
septal wall toward the apex. This branch is called the posterior descending artery. The right
coronary artery that continues on to the inferior wall of the left ventricle that transmits additional
branches that supply the inferior wall and they are typically called posteral(?) lateral arteries.
When the right coronary arteries supply the inferior wall of the left ventricle, the system is set to
be right dominant. In approximately 10-15% of the population, it is the lapsa(?) complex artery
that supplies the inferior wall, possibly the posterior descending artery as well. This system is
set to be left dominant. In the uncommon 5% of cases, both the right coronary and the left
circumflex artery supply the inferior wall. This arrangement is set to be co-dominant.
When angiography is performed with selective engagement of the coronary arteries, there is no
difficulty separating the artery from the veins. However, with the advance of magnetic
resonance angiography and computer tomography and geography, both the coronary arteries
could be visualized. Therefore, it is imperative to understand the cardiac venous anatomy well
so that the venous structure would not be confused as a patent artery which could be otherwise
occluded.
The coronary sinus that drains in to the right atrium receives its venous blood from two major
branches, the middle cardiac vein and the great cardiac vein. The middle cardiac vein is a
companion of the posterior descending artery. The greater cardiac vein travels along the left
atrial ventricular groove and it is a companion of the left circumflex artery. The coronary sinus
is typically very short, only 1-3 cm in length. Along the left atrial ventricular groove, the greater
cardiac veins receive drainage from various left ventricular venous branches. As the travel nears
the origin of the left circumflex artery, it diverges away from the left main coronary artery and
instead travels along the cores of the left descending artery. This portion of the vein is called the
anterior interceptal vein.
Venous drainage of the right ventricle is variable. They can collect into a small vessel called
small cardiac veins that drains directly into the right atrium. Various branches can also drain
separately into small openings in the right atrium. These are called Thebesian veins.
CONCLUSION
Compared with other organ systems, the cardiac anatomy is complex. It is also unique in that
motion is an intrinsic property of its function. The understanding of normal anatomy and its
variants and its complex motions are critical in different shading and diagnosing disease of the
heart, both congenital as well as acquired in nature. Currently this information obtained in
humans by means of chest radiographs, echocardiography, catheter based angiography, magnetic
resonance imaging, and cardiac gated computer tomography. These various modalities
compliment each other in terms of cross effectiveness, diagnostic accuracy, patient safety, and
clarity of presentation. Intelligent choices made by cardiology and cardiac radiologists are
critical in the optimal care of these patients afflicted by cardiac disease.
REFERENCES:
1. Benjamin Felson Chapter 11 Mediastinum Chest Rontgenology; 419 W.B. Saunders,
Philadelphia 1973