Chapter 23: The pericardium and heart
Pericardium
The heart is enclosed in a fibroserous sac termed the pericardium (figs. 23-1 and 23-2), which occupies the middle mediastinum (see fig. 20-8). The pericardium and its fluid lubricate the moving surfaces of the heart.
The fibrous pericardium is the outermost layer, and it is firmly bound to the central tendon of the diaphragm. Extrapericardial fat, which may be visible radiographically, is often found in the angles between the pericardium and diaphragm on each side. The pericardium is attached to the sternum (by the sternopericardial ligaments) and is adherent to the mediastinal pleura except where the two are separated by the phrenic nerves.
The serous pericardium (fig. 23-1) is a closed sac, the parietal layer of which lines the inner surface of the fibrous pericardium and is reflected onto the heart as the visceral layer, or epicardium. The potential space between the parietal and visceral layers contains a thin film of fluid and is known as the pericardial cavity.
Because of the manner in which the reflections of the pericardium occur during development at the arterial and venous ends of the heart, when the pericardial sac is opened anteriorly in the adult it is possible to pass a finger posterior to the aorta and pulmonary trunk (arterial end of heart) and anterior to the left atrium and superior vena cava (venous end of heart). This passage is termed the transverse sinus of the pericardium (figs. 23-1 and 23-2). The reflection at the venous end is complicated and occurs as an inverted U along the pulmonary veins and inferior vena cava: this recess is termed the oblique sinus of the pericardium.
The pericardium is supplied by several arteries that are in the area (e.g., the internal thoracic), and by the phrenic nerves, which contain vasomotor and sensory fibers. Pericardial pain is felt diffusely behind the sternum but may radiate.
Heart
The heart is situated in the middle mediastinum and is divided into right and left sides by an obliquely placed, longitudinal septum. Each side consists of an atrium, which receives blood from the pulmonary veins, and a ventricle, which propels the blood into the arteries. The heart is situated more in the left side of the thorax than in the right (see figs. 23-4 and 23-21). The adjective cardiac is derived from the Greek kardia, heart. The cardiac wall consists, from outside inward, of epicardium (visceral pericardium), myocardium, and endocardium. The epicardium contains variable amounts of fat that tends to aggregate along vessels and in the grooves on the surface of the heart.
Course of circulation
The superior and inferior venae cavae and the intrinsic veins of the heart discharge venous blood into the right atrium via the coronary sinus (fig. 23-3). The blood then enters the right ventricle, from which it is ejected into the pulmonary trunk, which, by way of the right and left pulmonary arteries, delivers blood to the lungs. The pulmonary veins return blood to the left atrium. The blood then enters the left ventricle and is ejected into the aorta. Four important valves are encountered: the right and left atrioventricular, known as the tricuspid and mitral valves, respectively, and the right and left semilunar, known as the pulmonary and aortic valves, respectively (see fig. 23-7). Insufficient closure results in an incompetent valve and reflux of blood.
Size and position
The size of the heart is frequently described as that of the person's fist. The surface area of the heart, as determined from PA chest x-rays, is used as an index of size.
When a subject is in the erect position, the heart (fig. 23-4) is lower than is generally illustrated. Radiographic data are frequently not in agreement with findings obtained by percussion, and locating the apex beat ("point of maximal impulse"; PMI) is probably a better guide to the left border than is percussion.
The so-called apex of the heart is often rounded and ill-defined radiographically. When recognizable, it is usually at the level of costal cartilage 6, below and medial to the point at which the apex beat can be felt. The so-called apex beat, which is an impulse imparted by the heart, can usually be felt on the front of the left side of the chest. The site of this point of maximum pulsation is generally in intercostal space 4 or 5, about 6 or 7 cm from the median plane. The apex beat is produced by a complex movement of the left ventricle during contraction. It is a fairly reliable guide to the left border of the heart, but in some people it is felt outside the cardiac area.
The atria, which form the base of the heart, lie posterior to the ventricles, and the right chambers contribute more to the front of the heart than do the left. The planes of the atrioventricular orifices are more vertical than horizontal; hence the blood flows almost horizontally forward from the atria to the ventricles (see fig. 23-3). The longitudinal axis of the heart, which extends from the base to the apex, is directed anterior, inferior, and to the left. Radiographically, the right heart border is comprised of the right atrium; the left heart border is the left ventricle; the anterior surface of the heart (closest to the sternum) is the right ventricle; and the posterior aspect (indenting the esophagus) is the left atrium. The size, shape, and position of the heart vary from one individual to another, and also from time to time in the same individual (see fig. 23-17). Tall, slender people are more likely to have "vertical" hearts, whereas obese or pregnant individuals are more apt to have "transverse" hearts. The position and movements of the diaphragm are the most important factors in determining the position of the heart. During deep inspiration, the heart descends and becomes narrower and more "vertical."
When a subject is in the supine position, the heart moves upward and backward. In the newborn and infant, the heart is relatively large, globular, "transverse," and higher than in the adult.
External features of heart (fig. 23-5)
The heart is usually said to have an apex, a base, and three surfaces: sternocostal, pulmonary (or left), and diaphragmatic. Borders are indefinite. The base, formed by the atria, is directed posterior, and it lies behind the ventricles. Each atrium continues forward, on each side of the aorta and pulmonary trunk, as an ear-shaped appendage termed the auricle. (In clinical usage, an atrium is sometimes still called an auricle and an auricle an auricular appendage.) The right atrium may show a slight groove, the sulcus terminalis, extending from the front of the superior caval orifice to the right side of the inferior caval opening. This sulcus corresponds with a muscular band interiorly, the crista terminalis. The sinu-atrial node is embedded within the upper part of the crista terminalis (near the superior vena caval orifice).
The atria and ventricles are separated by an atrioventricular (or coronary) groove. This grove is the location of the coronary sinus and the proximal portions of the coronary arteries (see fig. 23-9).
The sternocostal surface of the heart is formed mainly by the right ventricle, which is prolonged upward as the conus arteriosus, or infundibulum. A shallow anterior interventricular groove is the location of the anterior interventricular branch of the left coronary artery (LAD; left anterior descending artery). A posterior interventricular groove on the inferior or diaphragmatic surface of the heart, contains the posterior interventricular artery, which is usually a branch of the right coronary artery. The diaphragmatic surface is formed by both ventricles, whereas the left surface of the heart and the apex is mainly the left ventricle.
Internal features of atria (fig. 23-5)
The inner surfaces of both auricles present muscular ridges termed the pectinate muscles, whereas the inner aspects of the atria are mostly smooth.
The right atrium receives the openings of the superior and inferior venae cavae. The valve of the inferior vena cava (Eustacian valve) is a variable semilunar fold in anterior aspect of the orifice. The valve of the coronary sinus (Thebesian valve) is also variable. A ridge, the crista terminalis, separates the rough-walled part of the left ventricle from the auricular appendage, containing pectinate muscles. The interatrial septum, seen from the right side, presents an ovoid depression termed the fossa ovalis, which is bounded (most noticeably on the superior aspect) by a fold called the limbus fossae ovalis. The upper part of the fossa may be separated from the limbus by a variable aperture, the foramen ovale, which is the persistence of a fetal interatrial opening. The right atrioventricular orifice is guarded by the tricuspid valve, which usually can admit three fingers. The atrioventricular (A-V) node is located within the wall near the center of a triangle (the so-called triangle of Koch) which has a base formed by the attachment of the septal cusp of the tricuspid valve and an apex at the osteum of the coronary sinus. Damage to the atrium in this area can result in A-V conduction block.
The left atrium is prolonged on each side as pouches for the openings of the pulmonary veins. The fossa ovalis appears as a translucent area in the interatrial septum. The upper edge of this region is called the valve of the foramen ovale. The left atrioventricular orifice is guarded by the mitral valve, which usually can admit two fingers.
The right atrium is usually on the same side of the body as the eparterial (upper lobe) bronchus, the suprahepatic part of the inferior vena cava, and the liver (hepatocavo-atrial concordance). In some anomalies of alignment, a morphological right atrium may be present on the left side of the heart. Thus, in transposition of the viscera (situs inversus), the morphologically right cardiac chambers are generally on the left and the morphologically left chambers, including the apex, are frequently on the right.
The walls of all four chambers show a number of small foramina for the intrinsic veins of the heart (venae cordis minimae).
Internal features of ventricles (figs. 23-5, 23-6 and 23-7)
The ventricles of the heart have tricuspid and pulmonary openings on the right and mitral and aortic openings on the left. The inner surfaces of the ventricles are mostly irregular, because of the projection of muscular bundles known as trabeculae carneae. Three kinds occur: (1) "ridges" on the ventricular surface; (2) "bridges," free in the middle; and (3) "pillars," termed papillary muscles, the bases of which are attached to the ventricular wall. The apices are continued as fine strands, the chordae tendineae, which are anchored to the cusps of the atrioventricular valves and prevent eversion of those valves (see fig. 23-5).
Each atrioventricular valve has cusps that are attached to a fibrous ring around the opening (figs. 23-5 and 23-7). The atrial surfaces of the cusps are smooth, whereas the ventricular surfaces are rough to allow for attachment of the chordae tendineae.
The semilunar valves are situated at the roots of the pulmonary trunk and aorta (see fig. 23-5). Each has three cusps, and the free edge of each cusp has a small, fibrous thickening, the nodule, on either side of which is a thin crescentic area termed a lunule. When the valve is closed, the nodules and lunules are in apposition. The spaces between the cusps and the walls of the vessels "distally" are the pulmonary and aortic sinuses, respectively.
The terminology of the cusps of the semilunar valves is important in comparing congenital defects in which the great vessels are misaligned, out of position, or transposed. Nevertheless, the terminology is confusing because the cusps are frequently named (as in the Nomina anatomica) from the excised organ instead of being based (as in this book) on the relationships in situ (fig. 23-7).
The cardiac valves are not visible radiographically, unless calcified, but they can be seen during echocardiography and cardiac angiography. The aortic valve is situated in the middle of the cardiac shadow, as seen from the front, and the mitral valve is slightly inferior and to the left (cf. fig. 23-18).
The right ventricle is usually characterized by (1) a tricuspid valve, (2) a trabeculated septal surface, and (3) a supraventricular crest and conus arteriosus (infundibulum). (In some anomalies of alignment, a morphological right ventricle may be present on the left side of the heart.)
The right ventricle lies anterior to the right atrium, the plane of the tricuspid opening is nearly vertical, and the blood flows horizontally from the atrium to the ventricle (see fig. 23-3). The tricuspid (right atrioventricular) valve has three cusps: anterior, posterior, and septal (fig. 23-7). The associated papillary muscles are classified also as anterior, posterior, and septal. The septomarginal trabecula (or moderator band) is a bridge-type trabecula that extends from the interventricular septum to the base of the anterior papillary muscle. Its importance lies in the fact that it contains Purkinje fibers from the right limb of the atrioventricular bundle (cf. fig. 23-8).
The cavity of the right ventricle is U-shaped, but with the U on its side. The lower limb of the U, which receives blood from the right atrium, is the venous, or inflowing, part of the ventricle. The limbs of the U are separated by a muscular ridge termed the supraventricular crest. The upper limb, or conus arteriosus (or infundibulum), is the arterial, or outflowing, part of the ventricle, and it ends in the pulmonary trunk. The walls of the conus are usually smooth. The junction of the conus and pulmonary trunk contains dense fibrous tissue that encircles the pulmonary valve and is continuous with the cardiac skeleton.
The pulmonary valve in situ has two cusps (right and left) anterior and one posterior (see figs. 23-7 and 23-11).
The left ventricle is usually characterized by (1) a bicuspid valve, (2) a smooth septal surface, and (3) the absence of a crest or conus. (In some anomalies of alignment, a morphological left ventricle may be present on the right side of the heart.)
Because the arterial pressure in the systemic circulation is much higher than in the pulmonary circulation, the left ventricle performs more work; hence the wall of the left ventricle is usually more than twice as thick as that of the right.
The left ventricle lies mostly anterior to the left atrium, the plane of the mitral opening is nearly vertical, and blood flows obliquely forward from the atrium to the ventricle. The mitral (left atrioventricular) valve has two major cusps: anterior and posterior (see fig. 23-7). The associated papillary muscles are commonly the anterior and posterior.
The lower, or inflowing, part of the left ventricle receives blood from the left atrium (see fig. 23-19). The upper part, which has mainly fibrous walls, is known as the aortic vestibule, and it ends in the aorta. The junction of the vestibule and aorta contains dense fibrous tissue that encircles the aortic valve and is continuous with the cardiac skeleton.
The aortic valve in situ has generally one anterior cusp and two (right and left) behind (see figs. 23-7 and 23-11).
The interventricular septum (see fig. 23-6) is a strong, oblique partition consisting of muscular and membranous parts. One surface of the interventricular septum faces anterior and to the right and bulges into the cavity of the right ventricle. The other surface is posterior and to the left and is concave toward the left ventricle. The membranous part of the septum is the small, thin, smooth, fibrous, superior portion. The atrioventricular bundle is situated at the lower border of the membranous part. The septal cusp of the tricuspid valve is usually attached to the right side of the membranous part so that the most superior portion of the septum (between right atrium and left ventricle) is atrioventricular in position.
The cardiac skeleton (see fig. 23-7) consists of fibrous or fibrocartilaginous tissue that partially surrounds the atrioventricular and perhaps the semilunar openings and gives attachment to the valves and the muscular layers.
The myocardium is arranged in complicated sheets and bands. Apart from the conducting system, the atrial and ventricular musculatures are separate. The ventricular musculature comprises superficial spiral and deep constrictor sheets, and the heart is twisted during systole like a cloth being wrung out.
Conducting system
The conducting system (fig. 23-8) consists of specialized (i.e., impulse-conducting) muscle fibers that connect certain "pacemaker" regions of the heart with ordinary "working" cardiac muscle fibers. The intrinsic, rhythmic contractions of cardiac muscle fibers are regulated by pacemakers, and the intrinsic rhythmicity of the pacemakers is regulated in turn by nerve impulses from vasomotor centers in the brain stem. If the conducting system between the atria and ventricles is destroyed (complete heart block), the atria and ventricles beat at different rates.
The conducting system comprises the sinuatrial (S.A.) node, the atrioventricular (A.V.) node, and the A. V. bundle, with its two limbs and the subendocardial plexus of Purkinje fibers. The impulse begins at the S.A. node, activates the atrial musculature, and is thereby conveyed to the A. V. node. Special bundles (internodal tracts) of atrial muscle fibers pass more or less directly from the S.A. to the A.V. node, but their functional significance is unclear.
The S.A. node is the usual pacemaker for the heart. It is situated anterolaterally at the junction of the superior vena cava and the right atrium, near the upper end of the sulcus terminalis and immediately beneath the epicardium. It consists of a network of specialized cardiac muscle fibers, which are continuous with the atrial muscle fibers. The node is supplied by autonomic fibers and by a branch of the right (sometimes the left) coronary artery.
The A. V. node is situated beneath the endocardium of the right atrium, in the interatrial septum immediately anterosuperior to the opening of the coronary sinus. It consists of a network of specialized cardiac muscle fibers, which are continuous with the atrial muscle fibers and with the A.V. bundle.
The A. V. bundle leaves the A. V. node and ascends to the membranous part of the interventricular septum. It then runs anteriorward and divides into right and left limbs, or crura, which straddle the muscular part of the septum. The limbs proceed to the papillary muscles of their respective ventricles (the right limb traverses the septomarginal trabecula), and their fibers then ramify subendocardially as a plexus of Purkinje fibers. The bundle and crura are surrounded by a fibrous sheath.
Blood supply and innervation
The heart is supplied by the right and left coronary arteries (fig. 23-9), which usually arise from the right and left aortic sinuses, respectively (see figs. 23-7 and 23-11).
The right coronary artery emerges between the pulmonary trunk and right auricle. It usually supplies the S.A. node, conus arteriosus, right atrium, and right ventricle, and then winds to the posterior aspect of the heart, where it anastomoses with the left coronary artery. A posterior interventricular branch supplies the A. V. node and portions of both ventricles.
The left coronary artery emerges between the pulmonary trunk and left auricle, gives off an anterior interventricular branch (which descends to the apical region), supplies the left atrium, and, as the circumflex branch, winds to the posterior aspect of the heart, where it supplies the left ventricle and anastomoses with the right coronary artery. In many instances, the branch to the S.A. node arises from the circumflex branch (rather than from the right coronary artery), and the branch to the A. V. node may occasionally come from the left artery also. The anterior interventricular branch appears to be a direct continuation of the left coronary artery, and it provides the chief supply to the interventricular septum. It supplies the apical region and, on the posterior aspect of the heart, anastomoses with the posterior interventricular branch of the right coronary artery.
The heart is usually supplied equally by the two coronary arteries, but a preponderance of one vessel may occur. Variations and anomalies are relatively common. Thus, although the posterior interventricular branch arises from the right coronary in at least 90 per cent of hearts, it comes from the left coronary in approximately 10 per cent, in which case the left artery gives rise to both interventricular branches. These alternative arrangements are known as dominance of the right or of the left coronary artery, respectively.
The venous drainage of the heart is (1) partly by small veins that empty directly into the cardiac chambers and (2) partly by veins that empty into the coronary sinus (fig. 23-9). The coronary sinus is a short, wide trunk that lies in the coronary groove between the left atrium and left ventricle. Its tributaries include the small, middle, and great cardiac veins and the oblique vein of the left atrium. The coronary sinus opens into the right atrium between the openings of the inferior vena cava and the tricuspid valve. Its right side is guarded by a valve.
The heart is supplied by autonomic nerve fibers and by sensory fibers of the sympathetic trunks and vagi (fig. 23-10). There are many ganglion cells (mainly parasympathetic) and sensory nerve endings in and around the heart, especially in the atria and near the veins.
Preganglionic sympathetic fibers from the spinal cord (T1 to 6) synapse in cervical and thoracic sympathetic chain ganglia, and postganglionic fibers travel in cervical and thoracic cardiac branches of the sympathetic trunk. Preganglionic parasympathetic fibers in the vagi travel in cervical and thoracic cardiac branches of the vagi to synapse upon ganglion cells scattered in the cardiac plexus near the heart. The postganglionic fibers of both autonomic systems supply the S.A. and A.V. nodes and the coronary vessels. The arrangement of the various cardiac nerves is extremely variable.
Sensory fibers from complicated endings in the heart travel in the vagi. They are concerned with the reflex control of blood pressure, blood flow, and heart rate. Pain fibers from blood vessels in the heart proceed to the sympathetic trunks and enter the spinal cord (by dorsal roots T1 to 5). Cardiac pain is usually referred to the left shoulder and medial side of the left upper limb (ulnar distribution), although it may be felt in the chest.
Cardiac cycle
The contraction of the heart is termed systole, its relaxation is termed diastole. When the ventricles are filled, they begin to contract. The increased intraventricular pressure causes the A.V. valves to close, and the resultant vibrations are a major cause of the first heart sound. The A. V. valves are prevented from prolapsing into the atria by the contraction of the papillary muscles. When intraventricular pressures surpass those in the aorta and pulmonary trunk, the semilunar valves open and blood is ejected into these arteries. The highest arterial pressure reached during the ejection phase is the systolic blood pressure.
The closure of the semilunar valves is a major cause of the second heart sound. The ventricular musculature relaxes, and the intraventricular pressures become lower than those in the atria. The A.V. valves then open, and blood flows from atria to ventricles. The ventricles dilate as they fill (diastole), the arterial pressure reaches its minimum (diastolic blood pressure), and the atria contract. The electrical activity of the heart is recorded as an electrocardiogram (EKG). Diseased valves result in abnormal vibrations that may be heard as murmurs. If the heart stops beating, attempts can be made to start it by electrical stimulation or closed-chest cardiac massage.
Additional features
The development of the heart (figs. 23-11 and 23-12), its congenital anomalies, and fetal circulation (fig. 23-13) are all-important but complicated topics that are beyond the scope of this text.
Physical and radiological examinations (see figs. 23-14, 23-15, 23-16, 23-17, 23-18, 23-19 and 23-21)
As in the case of the lungs, the classic methods of physical examination-inspection, palpation, percussion, and auscultation -are employed, in that order. The apex beat is often both visible and palpable, but it may be diffuse and may even be outside the cardiac area. It is usually about 6 to 7 cm or more from the median plane and is generally in intercostal space 4 or 5. The resting heart rate is around 70 beats per minute, but considerable variation (50 to 90) occurs, and the neonatal rate is twice as fast. Percussion has limited value in assessing the cardiac outline. In auscultation, the area of maximum intensity of the heart sounds for each valve corresponds not to the anatomical location of the respective valve but to the area where the cavity in which the valve lies is nearest the body surface, as far as possible from other valves, and "distal" to the valve with reference to the blood flow. The areas of maximum audibility are: (1) for the pulmonary valve, over left intercostal space 2; (2) for the aortic valve, over right intercostal space 2; (3) for the mitral valve, over the apical region; and (4) for the tricuspid valve, over the lower part of the body of the sternum (fig. 23-14).
The chief radiographic methods used in the examination of the heart and great vessels are plain chest radiographs, echocardiography and special methods such as cardiac angiography, in which a radio-opaque medium is injected through a catheter placed in the ventricle (ventriculography) or in one of the coronary vessels (coronary angiography). The most common view of the heart is the plain PA chest radiograph (postero-anterior projection) (fig. 23-15). The right border of the cardiovascular shadow is generally formed by the right brachiocephalic vein, superior vena cava, right atrium, and inferior vena cava. The left border is formed by the arch of the aorta (constituting a prominence known as the aortic knob, or knuckle), pulmonary trunk, left auricle, left ventricle, and extrapericardial fat (fig. 23-16). The apical region is at the lower left part of the cardiac silhouette: if an apex is present, it is usually below the level of the diaphragmatic shadow. The cardiovascular shadow is generally oblique, but it may be transverse (especially in infancy, obesity, and pregnancy) or vertical (fig. 23-17). In a left anterior oblique (L.A.O.) view, the curve of the aorta is "opened" and the x-rays are frequently projected in the plane of the interventricular septum (figs. 23-18 and 23-21). Further views are shown in figure 23-19.
Cardiac position and configuration depend chiefly on the diaphragm, the position of which depends mainly on posture and respiration (fig. 23-20). When a subject is in an erect position, the heart lies at the level of thoracic vertebrae 7 to 10, and its lower border may be 5 cm below the level of the xiphisternal junction (see fig. 23-4). In recumbency, the heart rises about one vertebral level. During inspiration, the heart appears more vertical (fig. 23-20), and the hili of the lungs are more readily seen.
Cardiopulmonary resuscitation
Cardiopulmonary resuscitation (CPR) involves the combined use of closed-chest manual heart compression and direct mouth-to-mouth breathing. The "ABCs" are to keep the Airway open and to see that Breathing is restored and Circulation is re-established.
Additional reading
Hurst, J. w. (ed.), The Heart, 4th ed., Blakiston (McGraw-Hill), New York, 1978. Contains several important chapters on anatomy.
James, T. N., Anatomy of the Coronary Arteries, Hoeber (Harper), New York, 1961. Provides details of injection-corrosion preparations.
McAlpine, W. A., Heart and Coronary Arteries, Springer, New York, 1975. Superb color photographs.
Milhiet, H., and Jager, P., Anatomie et chirurgie du pericarde, Masson, Paris, 1956. A detailed account of the pericardium.
Walmsley, T., "The Heart." Vol. 4, Part 3, of Quain's Elements of Anatomy, 11th ed., Longmans, Green, London, 1929. A classic.
Wilcox, B.R., Cook, A.C., Surgical Anatomy of the Heart. Cambridge University Press, 2004.
Questions
23-1 What is the transverse sinus of the pericardium?
23-2 Where is the apex beat?
23-3 In which direction does blood flow from the atria to the ventricles?
23-4 What is the main component of the sternocostal surface of the heart?
23-5 What is the foramen ovale?
23-6 What is hepatocavo-atrial concordance?
23-7 What is the outflowing part of (a) the right ventricle and (b) the left ventricle termed?
23-8 Which important structure is situated at the lower border of the membranous part of the interventricular septum?
23-9 What is meant by dominance of the left coronary artery?
23-10 How does a left anterior oblique (L.A.O.) view show certain features to better advantage?
Figure legends
Figure 23-1 Schematic sagittal section through the heart and pericardium. Note how the serous layer of the pericardium is reflected onto the heart and forms a double layer.
Figure 23-2 Mirror images of the pericardial reflections. A, The reflections onto the heart, viewed from behind. The arrow indicates the transverse sinus of the pericardium. B, The heart removed, and the posterior part of the pericardium viewed from in front. The reflection at the veins forms an irregular continuous line that begins at the inferior vena cava, extends up to the lower right pulmonary vein, and turns to the left across the left atrium to the left pulmonary veins. The irregular space thereby bounded is the oblique sinus of the pericardium (arrow).
Figure 23-3 The circulation of blood through the chambers of the heart. Note that blood flows almost horizontally forward from the right atrium to reach the outflowing part (conus arteriosus, or infundibulum) of the right ventricle. M, mitral orifice; T, tricuspid orifice.
Figure 23-4 The cardiovascular shadow (of a "vertical" heart) in relation to the bony cage. Depending on posture and phase of respiration, the lower margin of the heart may be at a still lower level, as much as 5 cm below the xiphosternal joint (see fig. 23-5). See fig. 23-16 for the composition of the cardiovascular shadow.
Figure 23-5 The external and internal anatomy of the heart. A, Right atrium and right ventricle, showing the tricuspid orifice. The arrows indicate the circulation of the blood. An arrow in the fossa ovalis represents "probe patency" of the foramen ovale. The membranous part of the interventricular septum lies mostly under cover of the septal cusp. The asterisk indicates the supraventricular crest. The septomarginal trabecula is frequently called the moderator band. B, Interior of the left atrium, dorsal view. The openings of the pulmonary veins (variable in number) and the left side of the fossa ovalis can be seen. C, Cross section through the ventricles, showing the much thicker wall of the left ventricle and the curved shape of the interventricular septum. D, Left ventricle, showing the mitral valve. E, Aortic valve, spread out. F, Tricuspid valve, showing the papillary muscles, chordae tendineae, and cusps (or leaflets). A., anterior cusp of aortic valve; Ao., aorta; C.S., opening of coronary sinus; I.V.C., inferior vena cava; I.V.S., interventricular septum; L., left cusp of aortic valve; L.C., opening of left coronary artery; L. V., left ventricle; P., posterior cusp of tricuspid valve; P. T., pulmonary trunk; R., right cusp of aortic valve; R.C., opening of right coronary artery; R.V., right ventricle; S., septal cusp of tricuspid valve; S.V.C., superior vena cava. (Based on Testut and other sources.)
Figure 23-6 A, Longitudinal section of the heart to show the interventricular septum. B, Higher magnification to show the atrioventricular and interventricular septa.
Figure 23-7 A, Diagram of the cardiac valves and their cusps in situ, as seen from above. The coronary arteries are also shown. A, anterior cusp; A.I.V., anterior interventricular branch; A.V., branch to atrioventricular node; CB., circumflex branch; L., left cusp; L.C., left coronary artery; P., posterior cusp; P.I.V., posterior interventricular branch; R., right cusp; R.C, right coronary artery; S., septal cusp; S.-A, branch to sinu-atrial node. Cf. fig. 23-9. B, Cardiac skeleton seen from above. The arrangement of the anuli and trigona shown is based on J. Zimmerman, J. Alb. Einstein Med. Cent., 7:77,1959. CA, roof of conus arteriosus (or infundibulum).
Figure 23-8 The conducting system, showing the positions of the sinu-atrial and atrioventricular nodes. The atrium and right ventricle are opened, and the interventricular septum is exposed.
Figure 23-9 The coronary arteries and the veins that drain into the coronary sinus. The posterior interventricular branch (P/V), although usually a branch of the right coronary artery (RC), may arise from the circumflex branch (C) of the left coronary artery (inset). In B, the left marginal vein can be seen ascending to join the great cardiac vein. The posterior vein of the left ventricle ascends and the oblique vein of the left atrium descends to end in the coronary sinus. A/V, anterior interventricular branch; e, circumflex branch; Ce, great cardiac vein; LC, left coronary artery; Me, middle cardiac vein; P/V, posterior interventricular branch; Re, right coronary artery; S.-A, branch to sinuatrial node; Se, small cardiac vein. Cf. fig. 23-7.
Figure 23-10 The sympathetic and afferent (in blue) fibers to the heart. For vagal fibers, see fig. 24-7.
Figure 23-11 The partitioning of the truncus arteriosus, and the development of the semilunar valves. A, Truncus arteriosus. B, C, and D, An intermediate position during the rotation that the heart undergoes during development; the terminology used by some authors for naming the cusps is shown. E, The usual position of the valves of the adult heart in situ; the terminology used in this book is shown.
Figure 23-12 Scheme of the spiral septum in the truncus arteriosus and bulbus cordis.
Figure 23-13 The fetal and postnatal circulation. The differences in shading represent differences in oxygenation of the blood: the vessels with the darkest shading contain the least-oxygenated blood.
Figure 23-14 Areas of auscultation. Arrows indicate the direction of conduction of heart sounds from the valves: the sounds are heard best at the indicated points. P, pulmonary; A, aortic; M, mitral; T, tricuspid. The arrow B indicates the common limits of the area in which the apex beat may be felt.
Figure 23-15 The usual views used in fluoroscopy and radiography are anterior, posterior, right anterior oblique (R.A.O.; fencing position), left anterior oblique (LAO.; boxing position), and sometimes right and left lateral. (Based on Zdansky.)
Figure 23-16 Composition of the margins of the cardiovascular shadow. (Based on Zdansky.)
Figure 23-17 Types of cardiovascular shadows.
Figure 23-18 The heart and great vessels. The horizontal line indicates the level of bifurcation of the trachea. (Based on Zdansky.)
Figure 23-19 The heart and great vessels. The horizontal line indicates the level of bifurcation of the trachea. (Based on Zdansky.)
Figure 23-20 The shape of the heart at maximum inspiration and maximum expiration.
Figure 23-21 Horizontal section showing all four chambers of the heart. The left atrium is almost entirely on the back of the heart. The interventricular and interatrial septa are at approximately a 45-degree angle to the median plane. The "right heart" (blue arrow) lies in front of the "left heart" (red arrow). The outline of the arch of the aorta (with the origin of its three branches), as seen from above, has been included, although it would lie about three vertebrae higher than the plane of this section. The position of a film for a left anterior oblique (L.A.O.) projection is shown. In such a view (shown in miniature next to the film), the right and left portions of the heart would appear approximately equally separated along the line of the interventricular septum. Moreover, because the arch of the aorta passes almost directly backward, rather than transversely, its curve would appear well opened out. A valuable article on cardiac anatomy is that by R. Walmsley and H. Watson (Br. Heart J., 28:435-447, 1966). B.T., brachiocephalic trunk; C.C., left common carotid artery; I.V.S., interventricular septum; L.A., left atrium; L.5., left subclavian artery; L.V., left ventricle; M., mitral valve; R.A., right atrium; R.V., right ventricle; T., tricuspid valve; T.V., thoracic vertebra.