L 10 External Features of the Heart PDF

10 External features of the heart ILOs By the end of this lecture, students will be able to 1. Differentiate between the different surfaces and borders of the heart in relevance to the related structures and chambers. 2. Appraise the importance of the surface projection of the heart borders during c...

10 External features of the heart ILOs By the end of this lecture, students will be able to 1. Differentiate between the different surfaces and borders of the heart in relevance to the related structures and chambers. 2. Appraise the importance of the surface projection of the heart borders during cardiac examination. 3. Correlate the anatomical description of the pericardium to its clinical importance. Position of the heart: The heart is present in the mediastinum (the space between the lungs which also contains the major blood vessels, oesophagus, nerves and trachea. External features of the heart: It is a pyramidal, hollow, four chambered, muscular organ. It has an apex, a base, and two surfaces. The base is placed posteriorly, while the aapex is directed forwards, downwards and to the left. Surfaces of the heart: [figures 1,2,3] 1. Sternocostal (anterior) surface. 2. Posterior surface ( base). 3. Diaphragmatic surface (inferior surface). Figure 1: Sternocostal surface of the heart. Figure 2: Diaphragmatic surface and base of the heart. Page 1 of 6 Figure 3: surfaces of the heart. Sterno-costal Surface of the Heart: [figure 1] It is formed by the 4 chambers (the right atrium and left auricle , 2/3 of right ventricle, and 1/3 of left ventricle) but mainly by the right ventricle. The anterior part of each atrium is a wrinkled and has a flap like extension called an auricle. This surface is related to 1. Body of the sternum, 2. Costal Cartilage, 3. Anterior borders of both lungs and Pleura. There are two grooves in the sterno-costal surface: 1- Atrio-ventricular groove (coronary sulcus): which separates the atria from the ventricles. The coronary arteries lie in this groove. 2- Anterior inter- ventricular groove: separates the right from the left ventricle. It contains the anterior interventricular artery and the great cardiac vein. Posterior surface (base) of the Heart [figure 2] It is formed by the back of both; the left and the right atria (mainly the left). It lies opposite the middle four (5-8) thoracic vertebrae. The 4 pulmonary veins entering the left atrium, and the superior and inferior venae cavae entering the right atrium. Page 2 of 6 N.B: The coronary sinus can be seen between the back of the left atrium and the back of the left ventricle. The Diaphragmatic Surface [figure 2] This surface is triangular in shape and rests on the diaphragm. It is formed by both ventricles ( 2/3 by the left ventricle and 1/3 by the right ventricle) (mainly the left) Diaphragmatic surface contains Posterior interventricular groove which contains the posterior interventricular artery and the middle cardiac vein. Borders of the heart [figure 3] This surface is limited by 4 borders: 1- The right border is formed by the right Atrium. 2- The left border is formed by the left ventricle. 3- The upper border is formed by both atria mainly the left. This upper border is hidden by the ascending aorta and the pulmonary trunk. 4- The lower border is formed by the right ventricle and apex of left ventricle. N.B.: The anterior surface shows parts of each of the four chambers of the heart: 1. Right atrium (RA). 2. Left atrium (LA): It is not seen in this view as it is covered anteriorly by the pulmonary artery and the ascending aorta. Only its auricle can be seen. 3. Right ventricle (RV). Mainly 4. Left ventricle (LV). Most of the left ventricle is posterior. The left atrium makes the base of the heart. When the body is in the supine position (lying on its back), the heart rests on its base and the apex of the heart (the tip of the left ventricle) projects up and to the left. SURFACE ANATOMY OF THE HEART [figure 4] It is represented by a quadrilateral shape between four points : Point 1: Lower border of the left second costal cartilage 1.5 inches from the midline. Point 2: Upper border of the right third costal cartilage one inch from the midline. Page 3 of 6 Point 3: Right sixth costal cartilage half an inch from the midline. Point 4: Left fifth intercostal space 3.5 inches from the midline (mid clavicular line). How to locate the borders of the heart? - The upper border is represented by a straight line from point 1 to point 2. - The right border is represented by a curved line from point 2 to point 3. - The lower border is represented by a straight line (passing by the xiphisternal joint) from point 3 to point 4. - The left border of the heart is represented by a curved line from point 4 to point 1. Figure 4: Surface anatomy of the heart. Surface anatomy of the valves of the heart [figure 5] - They lie behind the left border of the sternum except the tricuspid valve which lies in the middle line. (PAMT) (3cc 3is 4cc 4is) 1- Pulmonary valve: Behind the left border of the sternum opposite the 3rd costal cartilage. 2- Aortic valve: Behind the left border of the sternum opposite the 3rd intercostal space. 3- Mitral valve: Behind the left border of the sternum opposite the 4th costal cartilage. 4- Tricuspid valve: In the mid line opposite the 4th intercostals space. Page 4 of 6 Figure 5: Surface anatomy of valves of the heart. Clinical note: It should be known that the Marking of the heart will be affected by posture, breathing(contraction of diaphragm pull the heart downwards) and by hypertrophy or dilatation of the ventricles. Here, the apex beat move from the 5th intercostal space in the midclavicular line to the 6th intercostal space in the mid axillary line. So, the apex beat is an important clinical landmark. THE PERICARDIUM The heart and its pericardium make up the contents of the middle mediastinum. The left and right phrenic nerves lie to the left and right of the pericardium respectively. It is formed of two parts: an outer Fibrous Pericardium and an inner Serous Pericardium. The outer fibrous pericardium [figure 6] It is conical in shape. It is a tough sac enclosing the heart and provides attachments to the adjacent structures. Anteriorly it is attached to the sternum. Posteriorly it is related to descending aorta and oesophagus. Figure 6: The fibrous pericardium. Page 5 of 6 The inner Serous Pericardium [figure 7] It is formed of two layers, which are continuous with each other. 1. Outer parietal layer lines the fibrous pericardium 2. Inner visceral layer covers the heart. The continuity between the two layers takes place at the points where the major blood vessels enter and leave the heart. Between the two layers is the pericardial cavity, which is a potential space that contains a small amount of fluid which facilitates the movement of the heart. Figure 7: Layers of the serous pericardium. Page 6 of 6