RADIOLOGY
AND CATHETER BASED ANGIOCARDIOGRAPHY
FRONTAL PROJECTION
RADIOLOGY
Radiologic examination is an essential part of the evaluation of cardiac disease. The size of the heart and identification of chamber enlargement and pericardial, cardiac, and coronary calcification, as well as information on heart function and hemodynamics, can be determined from chest radiography, fluoroscopic examination, and angiocardiographic observations.
The myocardium,
valves, and other heart structures have similar radiodensity and therefore cannot
be distinguished radiologically unless calcified. Similarly, the walls of the cardiac
chambers cannot be visually separated from the blood within unless the opacity
of the blood is increased by the injection of a contrast material. The outer borders
of the heart can be seen because the relatively homogeneous cardiac silhouette is
contrasted against the lucent, air containing lungs.
The shadow of the
heart seen on standard radiographs or by fluoroscopy is magnified and somewhat distorted.
At the target-to-film or screen distances customarily used, the x-ray beam diverges
as it passes through the patient. The structures farther from the film are more
magnified than those closer. The distortion can be largely eliminated if the x-ray
beam is composed of parallel rather than divergent rays. For most purposes, heart
size can be adequately estimated from the stan- dard 6-foot chest film by comparing
the apparent cardiac size with that of the thorax. Allowances must be made for the
degree of inspiration the higher the diaphragm, the larger the apparent size of
the heart and the age of the patient. An infant’s heart is relatively large compared
with the chest, whereas an older patient’s chest is often small in relation to the
heart.
Since the heart
is a three-dimensional (3D) structure and only two borders are seen in any one view,
radiographs need to be secured in several projections to bring the various chambers
and great vessels into profile. Plain films of the chest also allow an
evaluation of the pulmonary vasculature and the lung changes that may be associated
with heart disease. Increased size and tortuosity of the pulmonary arteries and
veins usually indicate a left-to-right shunt, whereas
decreased prominence of these vessels is associated with a right-to-left shunt.
When the pulmonary artery flow is greatly decreased, as in severe tetralogy of Fallot,
the vascular pattern in the lungs often is reticular and nondirectional rather than
an orderly radiation of vessels from the lung hilum. This indicates the presence
of a significant collateral flow through the bronchial arteries.
In congestive failure
or obstruction on the left side of the heart, as in mitral stenosis, the pulmonary
veins become engorged. If this progresses to pulmonary hypertension, the veins,
together with the peripheral pulmonary arteries, become quite small while the
central pulmonary arteries dilate and become bulbous.
Frontal
Projection
Most chest films
are made in the frontal projection, so this is the view of the heart usually seen,
often providing the first suggestion of cardiac disease. Frontal is the most
easily reproducible projection, and thus heart size generally is evaluated in this
view (see Plate 3-1). Enlargement of the left atrium and
left ventricle, as well as the right atrium, generally can be recognized in the
frontal projection. The right ventricle, although it forms no borders, can produce
characteristic changes in the cardiac contour.
The upper half of
the right contour of the cardiac silhouette is formed by the superior vena cava
(SVC) and the lower half by the lateral wall of the right atrium. The margin of
the SVC is straight, but that of the right atrium bulges outward. The angle between
these two contours represents the superior aspect of the right atrium. If the patient
takes a deep inspiration, an indentation on the right border of the heart can
be seen just above the diaphragm, identifying the junction of the inferior vena
cava (IVC) and right atrium.
On the left side,
the uppermost part of the cardiovascular silhouette is formed by the distal arch
of the aorta as it curves posteriorly and inferiorly to become the descending
thoracic aorta. This is seen as a localized bulge extending from the left
side of the mediastinum above
the right tracheobronchial
angle. This bulge usually produces a localized indentation on the left side of the
esophagus. In the presence of a right aortic arch, the bulge will be on the right
side and will displace the esophagus to the left. Immediately below the aortic bulge,
the main pulmonary trunk and left main pulmonary artery are border forming. A
small segment of the left cardiac silhouette below the pulmonary artery is formed
by the left atrial appendage. This segment normally is flat or slightly convex
and is continuous with the curve of the left ventricle, which forms the largest
part of the left border of the cardiac contour. The point of transition between
the normal left atrial appendage and the left ventricle usually cannot be identified
on radiographs.
The apex of
the heart is formed by the left ventricle. In the frontal projection the right ventricle
is completely hidden within the cardiac silhouette. Occasionally on deep inspiration,
a part of the diaphragmatic surface of the heart near the cardiac apex is disclosed.
An indentation in this region marks the interventricular sulcus between the
two ventricles.
Enlargement of the
right atrium causes outward bowing and increased curvature of the border of the
right side of the heart. When the right ventricle increases in size, the heart
enlarges to the left, the apex is usually lifted, and the groove of the interventricular
sulcus appears higher on the apex of the heart than normal. As it enlarges, the
right ventricle elongates as well as widens, resulting in elevation of the main
pulmonary artery. As the left ventricle enlarges, the cardiac apex is displaced
downward and to the left. Often the entire left cardiac border is displaced to the
left, becoming increasingly convex.
Left atrial enlargement
is detected in the frontal view primarily by dilatation of the left atrial appendage,
which produces a localized bulge of the left contour below the pulmonary artery segment.
In addition, the enlarged left atrium often increases the density of the central
part of the cardiac silhouette and, when sufficiently large, may elevate the
left main bronchus. With increasing dilatation, the right border of the left atrium
may be seen within the cardiac silhouette to the right of the spine, producing a
second curved contour medial to the right atrial margin. With further enlargement,
the left atrium may project behind and beyond the right atrium so that the left
atrium will form the right border of the cardiac shadow. The border of the right
atrium will then be seen within the shadow of the left atrium. Calcification
of the cardiac valves is most often caused by rheumatic valvulitis, calcific
aortic stenosis, or bacterial endocarditis and involves the mitral and aortic valves.
In the frontal projection the mitral valve lies to the left of the spine,
and as the heart beats, calcifications on this valve will describe a flat, elliptical
trajectory extending downward and to the left. The aortic valve is usually
projected over the left side of the spine and moves in a relatively straight line
upward and slightly to the right. Because of the overlapping shadows of the vertebral
bodies, small calcific deposits on the aortic valve may be difficult to detect in
the frontal view but are readily seen in the lateral projection. The pulmonic
(pulmonary) valve is projected to the left of the spine, higher than
the aortic and mitral valves, and moves vertically with the cardiac pulsation.
The tricuspid valve lies over the spine and moves in a horizontal plane.
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| RIGHT ANTERIOR OBLIQUE PROJECTION |
Right
Anterior Oblique Projection
The right anterior
oblique (RAO) view is used mainly to evaluate left atrial enlargement and abnormalities
of the right ventricular outflow (outlet) tract (see Plate 3-2). RAO is also the best projection
in which to study calcification of the mitral valve. During selective left ventricular
angiocardiography, the RAO view is used to evaluate mitral stenosis or insufficiency,
because the mitral valve is seen tangentially, and the left atrium is projected
entirely behind the left ventricle. RAO is the only view in which these two chambers
do not overlap. In a properly positioned RAO view, the shadow of the spine lies
to the left of the cardiac silhouette, and a thin vertical band of air-containing
lung separates the two structures. The aortic arch is foreshortened in this
view, and the descending aorta partially overlaps the vertebral column.
The right border
of the heart is formed by the right posterior aspect of the left atrium above
and the posterior border of the right atrium below. As the obliquity of the projection
is increased, more of the left atrium comes into profile.
The uppermost
part of the left border of the cardiovascular silhouette is almost vertical and
represents the ascending aorta. Just below this segment, the cardiac contour
slopes downward and to the left in a gentle curve and is formed by the outflow tract
(outlet) of the right ventricle and pulmonary trunk. The inferior continuation
of this curve is formed by the anterior wall of the left ventricle. As in the frontal
view, the body of the right ventricle is in contact with the diaphragm and cannot
be visualized.
The mitral valve
is seen almost tangentially and is projected over the midpart of the cardiac silhouette.
Because confusing overlapping shadows are absent and the direction of mitral valve
motion is perpendicular to the x-ray beam, calcification of the mitral valve is
best detected fluoroscopically in RAO projection. The elliptical orbit of the
valve is mainly directed horizontally. The aortic valve is thrown clear of the spine,
and although in contact with the upper border of the mitral valve, calcification
of the aortic valve can be recognized as it moves mostly in an up-and-down direction.
This projection also provides the greatest separation of the aortic and pulmonic
valves. The pulmonary valve lies at a level higher than the aortic valve and to
its left, touching the left border of the cardiac silhouette. The line of motion
of the pulmonic valve is directed upward and to the right. The tricuspid valve is
seen almost tangentially and slightly behind the mitral valve. The tricuspid valve
moves horizontally with the cardiac pulsation, and in the rare case of tricuspid
calcification, the valve is easily mistaken for a calcified mitral valve.
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| LEFT ANTERIOR OBLIQUE PROJECTION |
Left Anterior Oblique
Projection
Although no longer
used for plain chest radiographs, the left anterior oblique (LAO) view is useful
in evaluating the size of the left atrium and left ventricle during angiography
(see Plate 3-3). The aortic arch is seen
clearly because it is oriented approximately parallel to the film and is projected
with minimal foreshortening. A selective left ventricular angiocardiogram in the
left oblique projection is useful in the detection of a ventricular septal defect,
because most of the muscular interventricular septum and a part of the membranous
septum are seen tangentially.
The right border
of the cardiac contour is formed by the right atrium above and the right ventricle
below. As the degree of obliquity is increased, more of the right ventricle becomes
border forming. Enlargement of the right atrium increases the convexity of the
upper right cardiac border, whereas enlargement of the right ventricle usually results
in a more generalized increase in curvature of the upper right border.
The left
cardiac contour is formed mostly by the left ventricle, except for the upper quarter,
which is contributed by the left posterior aspect of the left atrium, directly beneath
the left main bronchus. Usually, in a proper 45-degree oblique view, the shadow
of a normal left ventricle will not extend to the left of the shadow of the spine;
extension of this shadow indicates an enlarged left ventricle. However, this sign
must be evaluated cautiously because with lesser degrees of obliquity, or if the
film is not made in full inspiration, a normal left ventricle may not clear the
spine. If the stomach is distended with air, the diaphragmatic surface of the left
ventricle can also be evaluated.
The left atrial
part of the cardiac contour is usually straight or minimally convex. An outward
bulging in this region denotes left atrial enlargement, probably its most sensitive
radiographic sign. The esophagus is pro- jected directly over the left atrial segment;
therefore barium must not be given until after the LAO film has been made, because
significant degrees of left atrial enlargement could be obscured. With greater degrees
of enlargement, the dilated left atrium will push the left main bronchus upward
and horizontally. The dilated atrium will also encroach on the clear space
below the aortic arch.
The greatest length
of the aortic arch is seen in the LAO view, and the origins of the great vessels
are maximally separated. Thus, LAO is the best projection for identifying aneurysms
of the aortic arch and for opacification studies of the aorta and great vessels.
The mitral valve
is seen almost directly en face. As a result, calcific deposits on the cusps may
be difficult to see because these move on an axis perpendicular to the fluoroscopic
screen, with minimal horizontal excursion. In addition, the mitral valve may be
hidden partially by the shadow of the spine. Calcification of the tricuspid valve
can be differentiated from that of the mitral valve by the complete separation of
the two valves in the LAO projection, with the tricuspid valve lying in the right
half of the cardiac silhouette. The LAO view is well suited for identifying calcification
of the aortic valve, which lies in the upper part of the cardiac silhouette, clear
of the spine, and moves along an axis directed upward and to the right. The pulmonic
valve is situated slightly higher than the aortic valve and moves upward and toward
the left.
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| LATERAL PROJECTION |
In plain radiographs
the lateral view is used primarily for evaluating the presence of right ventricular
(RV) enlargement, left atrial enlargement, and combined enlargement of the left
atrium and left ventricle. Lateral is also the best view for distinguishing between
calcification of the aortic and mitral valves. A selective RV angiocardiogram in
the lateral projection provides the best visualization of the outflow part of the
right ventricle and the pulmonic valve (see Plate 3-4).
In the lateral view
the heart is projected clear of the confusing shadows of the sternum and spine.
The anterior margin of the cardiac silhouette is formed by the apex and the RV outflow
tract. Normally, this abuts on the lower quarter or third of the anterior chest
wall. The upper two thirds of the anterior cardiac contour is formed by two
convex arcs, slanting upward and posteriorly. The lower, more oblique arc is formed
by the RV outflow tract, and the upper arc is formed by the ascending aorta. The
radiolucent lung is interposed between these two arcs and the sternum. As it enlarges,
the right ventricle bulges forward and progressively obliterates the retrosternal
space. Similarly, dilatation and tortuosity, or an aneurysm of the ascending aorta,
will encroach on the upper retrosternal space. The upper margin of the aortic arch
distal to the origin of the great vessels can usually be identified in the
lateral view.
The posterior border
of the heart is formed mostly by the posterior wall of the left atrium. Just above
the diaphragm, small parts of the right atrium and IVC come into profile. When enlarged,
however, the left ventricle may extend farther posteriorly than the right atrium,
forming the lower part of the posterior heart border as well. The esophagus lies
immediately behind the left atrium and left ventricle, and an enlargement of these
chambers will indent the anterior wall of the esophagus and displace it posteriorly.
If only the left atrium is enlarged, the indentation on the esophagus is localized
at the level of the upper half of the cardiac silhouette; the lower part of the
esophagus is in its normal position. When the left ventricle is enlarged as well,
it also pushes the esophagus posteriorly, and the backward curve of the
displaced esophagus is then continuous over the entire length of the cardiac
silhouette to the diaphragm.
Identifying localization
of a calcific deposit in the mitral or aortic valve may be difficult. This problem
can be resolved in the lateral view. If a line is drawn from the anterior costophrenic
sulcus to the point of bifurcation of the trachea, the aortic valve will lie above
and in front of this line, whereas the mitral valve will be below and posterior.
The mitral valve moves more or less horizontally in the lateral view, and the aortic
valve moves on a vertical axis that is tilted slightly anteriorly and upward. The
pulmonic valve is located above the aortic valve and more anteriorly, extending
to the anterior border of the cardiac shadow.
Chest radiography
and fluoroscopy demonstrate only the outer borders of the heart and great vessels.
Considerably more information is obtained when the blood is opacified by introducing
a radiopaque contrast medium into the vascular system to visualize the inner
borders of the cardiac chambers and vessels during catheter-based angiography. The
structure and motion of the cardiac valves can be studied, as well as cardiac
and pulmonary hemodynamics.
The basic
requirements for successful catheter-based angiocardiography are (1) rapid injection
of the radiopaque contrast material so that it flows as a bolus and (2) cineangiography
of the heart to follow the course of the contrast material. The iodinated
contrast medium can be injected into a peripheral vein, where it is carried to the
heart through the SVC or IVC, or it can be injected through a catheter directly
into a specific cardiac chamber, great vessel, or coronary artery. The latter technique,
selective angiocardiography, provides greater anatomic detail because the
contrast material reaches the chamber as a denser, more compact bolus and is not
diluted in the right atrium by nonopaque blood.
A catheter can be
placed in the right atrium, right ventricle, or pulmonary trunk by introducing the
catheter into a peripheral vein and then advancing it through the SVC or IVC. In
children the left atrium can usually be entered by manipulating a catheter in the
right atrium, across the foramen ovale. In adults a similar route is used; the
atrial septum is punctured by a trans- septal needle and a catheter advanced over
the needle into the left atrium. The left ventricle is reached by inserting a catheter
into a peripheral artery and passing it retrograde through the aortic valve into
the ventricle. If the catheter has the proper curve, it can be manipulated backward
through the mitral valve into the left atrium. The left ventricle can also be reached
by a transseptal catheter passed from the right atrium into the left atrium and
advanced through the mitral valve. The left ventricle can be punctured directly
through the anterior chest wall, however, and angiocardiography by this route
carries substantial risk and is no longer used.
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| ANTEROPOSTERIOR PROJECTION OF RIGHT-SIDED HEART STRUCTURES |
Frontal
Projection of Right Side of Heart
The right side of
the heart usually can be well visualized by venous angiocardiography as well as
selective injection (see Plate 3-5). In the frontal, or
anteroposterior (AP), projection the SVC and IVC lie in a straight line to the right
of the spine, entering opposite ends of the right atrium. The free wall of the right
atrium is thin and is represented by the space between the right border of the contrast-filled
atrium and the right border of the cardiac silhouette. Normally, this space is 2
to 3 mm in diameter; increased width of this space indicates a pericardial effusion
separating the wall of the right atrium from the pericardium.
The right atrial
appendage extends medially and upward from the upper part of the right atrium. The
tricuspid valve lies in an oblique plane relative to the AP projection, and the
line of attachment of its cusps is often seen as an ellipse overlying the spine.
The inferior margin of the tricuspid annulus lies adjacent to the entrance
of the IVC into the right atrium. The opening of the coronary sinus lies in the
same region. The clinicians must keep this in mind when catheterizing the right
ventricle, because a catheter that has entered the coronary sinus and has advanced
into the great cardiac vein will follow almost the identical course in the
frontal projection as a catheter that has crossed the tricuspid valve and lies
within the RV outflow tract. The left border of the tricuspid valve ring forms the
left border of the atrium and corresponds to the posterior margin of the tricuspid
valve. The right ventricle is in front of the atrium and extends to the right (or
anterior) border of the tricuspid valve. Therefore, within the elliptical projection
of the tricuspid valve, the atrium and ventricle overlie each other.
The right ventricle
is a triangular-shaped chamber that can be divided into two parts: a large,
trabeculated inflow part and a smooth, narrow outflow tract. In the frontal view
these two parts can be separated by a line drawn from the uppermost margin of the
tricuspid valve downward and to the left, toward the apex of the ventricle. This
line approximates the course of the septal and moderator bands. The RV inflow tract
lies below the line, and the RV outflow tract lies above the line, extending to
the pulmonic valve. The right border of the inflow part is formed by the tricuspid
valve and the left border by the interventricular septum. The diaphragmatic RV
surface is a free wall. The right border of the RV outflow tract is also a free
wall, formed by a sheet of muscle extending from tricuspid to pulmonic valve and
lying in front of the aortic root. A localized prominence in this sheet of muscle,
the crista supraventricularis, is projected en face in this view and cannot be identified.
The line of attachment of the tricuspid valve can often be seen during diastole
on a selective RV angiocardiogram, because contrast material is trapped between
the open valve cusps and the walls of the ventricle, while the orifice of the valve
is filled by nonopaque blood entering from the atrium.
The pulmonic valve
is projected partially en face and is not well visualized in the frontal view. The
pulmonary trunk is usually seen well, but its root may be obscured in part by the
RV outflow tract. The right pulmonary artery courses almost directly to the right,
and its greatest length can be seen in the AP projection, whereas the left pulmonary
artery is directed posteriorly and is foreshortened. A steep LAO or left lateral
view is best for the study of the left pulmonary artery. On a venous angiocardiogram,
a part of the right pulmonary artery is often obscured by contrast material in the
SVC or right atrium, especially if this chamber is enlarged.
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| LATERAL PROJECTION OF RIGHT-SIDED HEART STRUCTURES |
Lateral Projection of Right
Side of Heart
In the lateral view
the right atrium is projected almost entirely behind the right ventricle (see Plate 3-6). The posterior border of the atrium is a free
wall. The interatrial septum lies in an oblique plane and cannot be visualized
in either the frontal or the lateral projection. The septum is seen tangentially
only in a steep right posterior oblique view. The anterior margin of the right atrium
is formed by the tricuspid valve. The atrial appendage arises at a level higher
than the valve and extends anteriorly and superiorly. The appendage is triangular
shaped, its base continuous with the atrial cavity. The border of the atrial appendage
cavity is irregular because of the pectinate muscles.
The ostium of
the coronary sinus lies in the inferior part of the atrium just in front of the
entrance of the IVC, and the great cardiac vein extends along the posterior aspect
of the heart. Therefore a catheter passed through the SVC that has entered the great
cardiac vein will curve posteriorly in the lateral view rather than anteriorly,
as occurs when the catheter traverses the tricuspid valve to enter the right ventricle.
The right ventricle is best
studied by selective angiocardiography because in the lateral view the opacified
right atrial appendage, especially if large, often extends far enough
anteriorly to obscure part of the RV outflow tract or the pulmonic valve. On a selective
study the tricuspid valve can usually be identified as an oblique ring on the posterior
aspect of the ventricle. The anterior border of this ring corresponds to the right
margin of the tricuspid valve. The main body of the right ventricle, the inflow
part, lies directly in front of the tricuspid valve. Just above the upper level
of the tricuspid valve, the ventricle becomes narrowed because of the intrusion
of a soft tissue mass on the posterior aspect. This represents the crista supraventricularis
and marks the level of the entrance to the infundibulum, the RV outflow tract. The
anterior border of the RV cavity forms a continuous curve to the pulmonary valve.
The pulmonic valve
and its cusps are easily identified in the lateral view, which is an ideal projection
for the study of pulmonic valvular stenosis. The lateral view not only can show
the limitation in the opening of the valve cusps, but also allows study of the infundibular
region and evaluation of associated infundibular stenosis. The pulmonary trunk courses
upward and back- ward, continuing the curve of the anterior RV wall. The left pulmonary
artery is well seen in the lateral view because it courses posteriorly, whereas
the right pulmonary artery is foreshortened.
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| ANTEROPOSTERIOR PROJECTION OF LEFT-SIDED HEART STRUCTURES |
Frontal
Projection of Left Side of Heart
The left atrium
lies partly above and to the right of the left ventricle (see Plate 3-7). The
upper border of the atrial cavity in the frontal (AP) view is straight, slanting
upward and to the left. The lower margin is bowed downward. The part of the lower
atrial margin that crosses the left ventricular (LV) chamber is formed by the inferior
margin of the mitral valve. The two superior pulmonary veins enter the uppermost
part of the atrium, and the inferior pulmonary veins enter at a slightly lower
level. The left atrial appendage often has a hooklike contour in the AP view, extends
to the left border of the heart and overlies the left superior pulmonary vein. It
may be difficult to distinguish fluoro- scopically whether a catheter in the left
atrium has entered the atrial appendage or the left superior pulmonary vein. This
can be resolved by viewing the patient in an oblique or lateral projection, because
the pulmonary vein extends posteriorly while the appendage lies anteriorly, or by
injecting a small quantity of contrast material and outlining the structure.
The left ventricle
differs basically from the right ventricle in that the inflow (mitral) valve and
the outflow (aortic) valve lie adjacent to each other. Indeed, the anterior cusp
of the mitral valve arises from a common annulus with part of the aortic valve.
The LV body lies below the two valves, rather than interposed as in the right ventricle.
The left ventricle is oval shaped, with its apex pointing downward and to the left.
The trabeculation of the LV body is finer than the RV trabeculation. On a selective
LV injection the inferior part of the mitral valve ring can usually be identified
as a curvilinear interface between the contrast material trapped under the posterior
mitral cusp and the nonopaque blood entering from the left atrium above. The superior
margin of the mitral ring is continuous with the aortic ring and usually is not
well seen in the frontal view. During ventricular systole, the mitral cusps bulge
toward the left atrium, the valve orifice is obscured by the contrast material in
the ventricle, and the line of attachment of the cusps can no longer be observed.
Fingerlike indentations arising from the left and right margins of the ventricle
are often seen during systole intruding into the ventricular lumen, representing
the papillary muscles.
The location of
the membranous part of the inter-ventricular septum can be determined in relation
to the aortic valve by ventriculography. It lies beneath the anterior part of
the posterior (noncoronary) cusp and a small part of the adjacent right (coronary)
cusp and the commissure between the two. In the AP projection the right cusp
is seen en face, the left cusp forms the left border of the aortic valve, and the
noncoronary cusp forms the right border. The membranous septum thus forms a segment
of the right LV border immediately beneath the aortic valve.
The right coronary
artery arises from the midpart of the aortic valve in the AP view and extends slightly
to the right and downward, running in the sulcus between the right atrium and ventricle.
The left coronary artery originates from the left border of the aortic valve. The
anterior descending branch courses downward in the interventricular sulcus overlying
the left part of the left ventricle. The circumflex branch curves to the right,
paralleling the inferior attachment of the mitral valve as it runs in the sulcus
between the left atrium and ventricle on the posterior aspect of the heart. The
relationships of the structures on the right and left sides of the heart can be
appreciated when the drawings
of the two ventricles and their great vessels are superimposed. The ventricles,
for the most part, are projected on top of one another. The RV outflow tract is
directed upward and toward the left, whereas blood in the left ventricle reaches
the aorta by passing upward and to the right. Thus the outflow tracts cross each
other, the left passing behind the right. Almost the entire right border of the
left ventricle is formed by the interventricular septum, with the uppermost part
membranous and the remainder muscular. In addition, a segment of the upper left
LV border also represents the interventricular septum. This is the basal part of
the muscular septum, which lies in the lower part of the infundibulum just above
the septal band on the right side. The uppermost margin of the tricuspid valve attachment
reaches almost to the aortic valve, and the origin of the septal cusp of the tricuspid
valve actually crosses the membranous septum. Thus the membranous septum on the
left side lies completely within the left ventricle, whereas on the right side the
anterior part lies in the right ventricle (interventricular septum), and the
posterior part lies behind the tricuspid valve in the right atrium
(atrioventricular septum).
The upper outflow
tract of the right ventricle lies above the left ventricle at the level of the
aortic sinuses of Valsalva. The pulmonic valve is at a level higher than the
aortic valve, and the two valves touch only near the commissures between right and
left cusps.
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| ANTEROPOSTERIOR PROJECTION OF LEFT-SIDED HEART STRUCTURES |
Lateral
Projection of Left Side of Heart
In the lateral view
the left atrium is projected almost completely behind the left ventricle (see Plate
3-8). The anteroinferior margin of the atrium is formed by the mitral valve. The
left atrial appendage (auricle) arises somewhat above the mitral valve and extends
anteriorly, crossing the aorta just above the sinuses of Valsalva. If the atrial
appendage is sufficiently large, its tip may overlie the pulmonic valve. The posterior
border of the atrial cavity is formed by the free wall of the atrium, and the pulmonary
veins enter its upper and middle parts.
On a selective LV
angiocardiogram the line of insertion of the mitral cusps can usually be seen
during diastole as an opaque ring surrounding the radiolucent blood within the valve
orifice. The mitral valve forms the posterior boundary of the ventricle. The upper
margin of the mitral valve reaches the aortic valve in the region of the commissure
between the left (coronary) and posterior (noncoronary) cusps. The LV body extends
forward and downward from the mitral valve. The posteroinferior border of the LV
body is formed by the free ventricular wall, and the entire ante- rior border is
bounded by the interventricular septum. The papillary muscles may sometimes be seen
as radiolucent defects arising from the midpart of the lower border of the ventricle
and directed toward the mitral valve.
In the lateral view
the right coronary cusp of the aortic valve is seen tangentially, forming the valve’s
anterior border. The left and posterior cusps are projected obliquely and lie posteriorly,
with the posterior (noncoronary) cusp always the lower of the two. The membranous
part of the interventricular septum directly below the commissure between right
and non-coronary cusps is not border forming. The superior part of the muscular
septum is directly in front of the membranous septum and forms the anterior subvalvular
border of the left ventricle.
The right
coronary artery arises from the upper part of the right sinus of Valsalva and courses
anteriorly a short distance before curving almost directly down-ward. The main trunk
of the left coronary artery is parallel to the x-ray beam and is foreshortened in
this view. Its circumflex branch parallels the posterior aspect of the mitral ring.
The left anterior or descending branch extends anteriorly and downward, overlying
the aortic root, then courses over the right sinus of Valsalva slightly below the
origin of the right coronary artery and crosses this artery, so that the lower part
of the anterior descending branch is the most anterior of the major coronary vessels.
When the right ventricle is enlarged, the sulcus between the ventricle and the right
atrium is displaced anteriorly. The right coronary artery lies within this sulcus
and in the lateral view is seen completely in front of the left anterior descending
branch. In this way, RV enlargement can be recognized on a selective LV angiocardiogram.
When lateral views of the right and left ventricles are superimposed, the tricuspid valve lies anterior to the mitral valve. The upper margin of the tricuspid valve marks the anterior extent of the atrioventricular septum, and the mitral valve marks the posterior extent. The interventricular portion of the membranous septum lies anterior to the insertion of the tricuspid valve. The supraventricular crest is directly in front of the right sinus of Valsalva, and most of the RV outflow tract thus is at a higher level than the left ventricle. Actually, a small part of the LV outflow tract immediately below the commissure between right and left aortic cusps does reach the same level as the subpulmonic region of the right ventricle. The RV and LV outflow tracts are separated in this area by the ventricular septum, and a defect in this region will produce a subpulmonic ventricular septal defect.
