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Anatomy of the Heart: Difference between revisions
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|bgcolor="lightblue" align="center"| | |bgcolor="lightblue" align="center"|Cardiac Anatomy Author | ||
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|S. Yen Ho | |<b>S. Yen Ho</b> PhD FRCPath FESC FHEA | ||
Royal Brompton Hospital | |||
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[[Image:Figure1.jpg|thumb|right|The endocast is viewed from 5 different perspectives to demonstrate the spatial relationship between right (coloured blue) and left (coloured red) heart chambers and between atria and ventricles. The blue and white arrows represent the right and left ventricular outflow tracts respectively.]] | [[Image:Figure1.jpg|thumb|right|The endocast is viewed from 5 different perspectives to demonstrate the spatial relationship between right (coloured blue) and left (coloured red) heart chambers and between atria and ventricles. The blue and white arrows represent the right and left ventricular outflow tracts respectively.]] | ||
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The cardiac silhouette is generally taken to be trapezoidal in shape. The rib cage provides good markers for charting the cardiac silhouette. The normal position of the cardiac apex is generally taken to be in the fifth intercostal space in the mid-clavicular line. The lower border is a nearly horizontal line in the area of the left sixth rib to the right sixth costal cartilage (Figure 2). The upper border is hidden behind the sternum at the level of the second and third cartilages. The right margin of the heart peeps out behind the right border of the sternum between the right third and sixth cartilages. In the infant, the upper part of the cardiac shadow is broad owing to the prominence of the overlying thymus gland. | The cardiac silhouette is generally taken to be trapezoidal in shape. The rib cage provides good markers for charting the cardiac silhouette. The normal position of the cardiac apex is generally taken to be in the fifth intercostal space in the mid-clavicular line. The lower border is a nearly horizontal line in the area of the left sixth rib to the right sixth costal cartilage (Figure 2). The upper border is hidden behind the sternum at the level of the second and third cartilages. The right margin of the heart peeps out behind the right border of the sternum between the right third and sixth cartilages. In the infant, the upper part of the cardiac shadow is broad owing to the prominence of the overlying thymus gland. | ||
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|[[Image:Figure3.jpg|thumb|The long axis of the heart is at an angle to the long axis of the body. Approximately a third of the heart is to the right of the midline of the sternum and the remainder is to the left of the midline.]] | |||
|[[Image:Figure3A.jpg|thumb|A. Viewed from the front, the right atrium and right ventricle overlaps the left atrium and left ventricle. The atrial chambers are to the right of their respective ventricular chambers.]] | |||
|[[Image:Figure3B.jpg|thumb|B. The four cardiac valves are at different levels and different planes with the pulmonary(P) valve situated the most cephalad. The aortic(A) valve is wedged between the tricuspid(T) and mitral(M) valves.]] | |||
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Inferior to the thymus, a fibrous pericardial sac encloses the mass of the heart. The sac has cuff-like attachments around the adventitia of the great arteries and veins as they enter or emerge from the heart. The pericardial cavity is contained between the double-layered serous pericardium. The parietal pericardium is adherent to the fibrous pericardium while the visceral layer is densely adherent to the cardiac surface forming the epicardium. Due to the contours of the heart and great arteries there exist two recesses within the pericardial cavity. These are the transverse and oblique sinuses. The transverse sinus occupies the inner heart curvature and lies between the posterior surface of the great arteries and the anterior surface of the atrial chambers. The reflection of the serous pericardium around the four pulmonary veins and the inferior caval vein forms the oblique sinus. | Inferior to the thymus, a fibrous pericardial sac encloses the mass of the heart. The sac has cuff-like attachments around the adventitia of the great arteries and veins as they enter or emerge from the heart. The pericardial cavity is contained between the double-layered serous pericardium. The parietal pericardium is adherent to the fibrous pericardium while the visceral layer is densely adherent to the cardiac surface forming the epicardium. Due to the contours of the heart and great arteries there exist two recesses within the pericardial cavity. These are the transverse and oblique sinuses. The transverse sinus occupies the inner heart curvature and lies between the posterior surface of the great arteries and the anterior surface of the atrial chambers. The reflection of the serous pericardium around the four pulmonary veins and the inferior caval vein forms the oblique sinus. | ||
When the pericardium is removed, the major part of the heart visible from the front is the ventricular mass. Here, the morphologically right ventricle occupies the greater part (Figure 3). The left ventricle appears only as a narrow slip along the left cardiac border. The shape of the heart is generally likened to a pyramid | When the pericardium is removed, the major part of the heart visible from the front is the ventricular mass. Here, the morphologically right ventricle occupies the greater part (Figure 3). The left ventricle appears only as a narrow slip along the left cardiac border. The shape of the heart is generally likened to a pyramid. The apex points downwards, forwards and to the left while the base faces posteriorly and to the right. While the cardiac apex is usually represented by the vortex of the left ventricle, the cardiac base is less well defined owing to differences in definition. The anatomical base is formed mainly by the left atrium receiving the pulmonary veins and to a small extent by the posterior part of the right atrium. The base in clinical practice, however, refers to the portion of the heart near the parasternal parts of the second intercostal spaces. The cardiac long axis, therefore, lies in a line drawn from the left hypochondrium towards the right shoulder. This orientation deviates considerably from the long axis of the body. Furthermore, the position of the cardiac septum at about 45º to the median brings the ‘right heart’ structures anterior to the ‘left heart’ structures (Figure 3A). The ventricles are situated inferior and leftward relative to their corresponding atria. This results in the right atrioventricular junction being in a nearly vertical plane. The left atrium is the most posterior cardiac chamber being directly anterior to the oesophagus at the bifurcation of the trachea. In frontal projection, only its appendage is visible. The aorta has a deep-seated origin and only becomes part of the cardiac silhouette as it arches upwards and backwards, forming a spiral with the pulmonary trunk. [[Image:Figure4.jpg|thumb|right|A. This frontal view shows the right and left surfaces of the heart. The left anterior descending coronary artery buried in epicardial fat marks the plane of the ventricular septum. | ||
B. The obtuse and acute margins of the ventricles are demonstrated in this apical view.]]The cardiac valves are offset from one another, in keeping with the disposition of the cardiac chambers and great arteries. When viewed in frontal projection, the pulmonary valve, being the most superior valve, is horizontally situated behind the third costal cartilage. The aortic valve lies posterior and to the right, above the nearly vertically orientated tricuspid valve (Figure 3B). The mitral valve is further posterior, overlapped by the more anterior but inferior tricuspid valve. The aortic valve therefore occupies a central position in the heart, wedged between the two atrioventricular valves. | B. The obtuse and acute margins of the ventricles are demonstrated in this apical view.]]The cardiac valves are offset from one another, in keeping with the disposition of the cardiac chambers and great arteries. When viewed in frontal projection, the pulmonary valve, being the most superior valve, is horizontally situated behind the third costal cartilage. The aortic valve lies posterior and to the right, above the nearly vertically orientated tricuspid valve (Figure 3B). The mitral valve is further posterior, overlapped by the more anterior but inferior tricuspid valve. The aortic valve therefore occupies a central position in the heart, wedged between the two atrioventricular valves. | ||
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==The morphologically right atrium== | ==The morphologically right atrium== | ||
[[Image:Figure5.jpg|thumb|right]] | [[Image:Figure5.jpg|thumb|right|A. This right lateral view shows the right atrium dominated by its large, triangluar shaped appendage. The dots mark the terminal groove. The arrow indicates the crest of the appendage. | ||
B. The lateral wall of the appendage incised and flipped backward to show the pectinate muscles and the thin, membrane-like atrial wall between the muscle bundles. The terminal crest (dots) marks the border between the pectinated appendage and the smooth-walled venous sinus. The oval fossa is surrounded by its muscular rim. The smooth-walled vestibule leads to the tricuspid valve orifice.]] | |||
The right atrium is composed of an anterior appendage, a posterior venous sinus, a septal portion and a vestibule. The junction between the appendage and the venous sinus is marked epicardially by an atrial groove the terminal groove, in which lies the sinus node. Inside the chamber, the terminal groove is represented by a muscle bundle, the terminal crest (crista terminalis), from which pectinate muscles radiate into the appendage (Figure 5). The appendage has a characteristic triangular shape and a wide communication with the venous sinus. The smooth-walled venous sinus receives the superior and inferior caval veins in its cephalic and caudal extremities respectively. The coronary sinus opens close to the septal portion and near the opening of the inferior caval vein. The outlet portion of the atrium, the vestibule leading to the tricuspid valve orifice, is also smooth walled. The obliquely orientated atrial septum extends from right posterior to left anterior position. When viewed from the right atrial aspect, the atrial septum is characterised by a muscular rim – the limbus - which surrounds the flap valve of the oval fossa (Figure 5). The extent of the true septum, however, is limited to the flap valve and the immediate part of its surrounding muscular rim. On the epicardial side much of the rim is filled by the interatrial groove which separates the right atrium from the right pulmonary veins posteriorly and superiorly. In its anterior part, the infolded rim contains the continuation of the interatrial groove and its musculature extends to the anterior wall of the right atrium, directly related to the transverse pericardial sinus. Only a small portion of the inferior rim is part of the true atrial septum. Its major portion is the continuation of the right atrial wall, the vestibule, overlying the crest of the ventricular septum (Figure 5). In fetal life, the flap valve of the oval fossa allows venous return mostly from the inferior caval vein to enter the left atrium. After birth the valve is normally large enough to close the interatrial communication as higher left atrial pressure pushes the valve against the muscular rim forming a complete seal. A probe patency (a probe could be passed from right to left atrium through an unsealed antero-superior part of the rim) exists in about a quarter of the normal population and is generally referred to as a PFO. | The right atrium is composed of an anterior appendage, a posterior venous sinus, a septal portion and a vestibule. The junction between the appendage and the venous sinus is marked epicardially by an atrial groove the terminal groove, in which lies the sinus node. Inside the chamber, the terminal groove is represented by a muscle bundle, the terminal crest (crista terminalis), from which pectinate muscles radiate into the appendage (Figure 5). The appendage has a characteristic triangular shape and a wide communication with the venous sinus. The smooth-walled venous sinus receives the superior and inferior caval veins in its cephalic and caudal extremities respectively. The coronary sinus opens close to the septal portion and near the opening of the inferior caval vein. The outlet portion of the atrium, the vestibule leading to the tricuspid valve orifice, is also smooth walled. The obliquely orientated atrial septum extends from right posterior to left anterior position. When viewed from the right atrial aspect, the atrial septum is characterised by a muscular rim – the limbus - which surrounds the flap valve of the oval fossa (Figure 5). The extent of the true septum, however, is limited to the flap valve and the immediate part of its surrounding muscular rim. On the epicardial side much of the rim is filled by the interatrial groove which separates the right atrium from the right pulmonary veins posteriorly and superiorly. In its anterior part, the infolded rim contains the continuation of the interatrial groove and its musculature extends to the anterior wall of the right atrium, directly related to the transverse pericardial sinus. Only a small portion of the inferior rim is part of the true atrial septum. Its major portion is the continuation of the right atrial wall, the vestibule, overlying the crest of the ventricular septum (Figure 5). In fetal life, the flap valve of the oval fossa allows venous return mostly from the inferior caval vein to enter the left atrium. After birth the valve is normally large enough to close the interatrial communication as higher left atrial pressure pushes the valve against the muscular rim forming a complete seal. A probe patency (a probe could be passed from right to left atrium through an unsealed antero-superior part of the rim) exists in about a quarter of the normal population and is generally referred to as a PFO. | ||
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8. Koch W. Der funktionelle Bau des menschlichen Herzens. Berlin: Urban v Schwarzenburg,1922:92. | 8. Koch W. Der funktionelle Bau des menschlichen Herzens. Berlin: Urban v Schwarzenburg,1922:92. | ||
9. Rosenbaum MB, Elizari MV, Lazzari JO. The hemiblocks. In: Tampa Tracings. Oldsmar, Fla. 1970. | 9. Rosenbaum MB, Elizari MV, Lazzari JO. The hemiblocks. In: Tampa Tracings. Oldsmar, Fla. 1970. PMID: 5051397 | ||
</biblio> | </biblio> | ||