Lancashire & South Cumbria Cardiac Network ANATOMY & PHYSIOLOGY MANUAL Cardiac Physiologist Training Manual ANATOMY OF THE HEART Surface Anatomy and Position The Anterior surface or sternocostal surface of the heart is formed mainly by the right ventricle. To the left is a small section of the left ventricle separated from the right by the anterior interventricular groove that carries the anterior descending branch of the left coronary artery. A small right atrial portion is found on the right. This anterior surface lies directly behind the sternum from which it is separated by the pericardium. The pleura and thin anterior parts of the lungs also partly cover it except for a small triangular area, the cardiac incisure in the left lung. The superior border is formed by the upper margins of the atria, mainly the left. It is largely hidden by the ascending aorta and pulmonary trunk. The superior border extends from the upper part of the left 2nd intercostal space to the lower part of the same space on the right. This line also marks the line of the pulmonary arteries which lie along this border of the heart. The SVC enters the right atrium at the right. The right border extends from the right end of the superior border to the right 6th costal cartilage, 1-2cm from the sternum. This convex border is formed by the right atrium and is vertical, the SVC and IVC entering in a vertical line at the top and bottom respectively. The left border is marked by a convex line joining left ends of the superior and inferior borders. It is formed by the left ventricle except for a small part of the left atrium and its appendage at the top. The inferior border extends from the lowest part of the right border to the apex of the heart. The apex is at the 5th intercostal space slightly median to the mid-clavicular line and is formed from the left ventricle. The position of this border varies slightly in the standing and supine position as well as respiratory movements. The lower border is formed mainly from the right ventricle but the larger part of the lower surface which is immediately above the diaphragm is formed by the left ventricle. It carries the posterior interventricular groove, which carries the posterior descending artery. The posterior surface, vertebral surface or base is formed mainly by the left atrium and to a small extent by the posterior part of the right atrium. It is separated from the thoracic vertebrae 5th-9th by the pericardium, right pulmonary veins, oesophagus and aorta. At its junction with the diaphragmatic surface is the posterior part of the coronary sulcus containing the coronary sinus. LJR.A.001.01 Z:\Manuals\A & P manual.doc 2 Created by ButlerL, BouncirG, Burnett G, Created on 16/01/2004, Edited on 19/07/2004 INTERNAL STRUCTURE OF THE HEART The Atria RIGHT ATRIUM A quadrangular shaped chamber, which forms the right border of the heart. The SVC enters at the upper posterior part. Anterior and lateral to it is the right lung. Posterior to it is the intra-atrial septum. Medial to it is the ascending aorta and pulmonary artery. It’s interior consists of 2 parts: (1) Sinus Venosus (venarium) Has a smooth thin wall and is formed from the foetal sinus venosus, which is absorbed into the right atrium. The great veins enter this part. The SVC at the upper posterior part, opening downwards and forwards. The IVC enters the lower posterior part just above the diaphragm. At its entrance is a rudimentary valve, the eustacian valve which in the embryo directs the blood from the IVC to the left atrium. The coronary sinus, the main vein of the heart, enters between the IVC and AV opening, close to and immediately posterior to the AV orifice. At its entrance is a rudimentary valve, the thesbian valve. The IVC lies to it’s right. (2) Atrium Proper Lies anterior to the sinus venosus. It is derived from the primitive atrium and is continuous with the auricle. The crista terminalis is a vertical ridge of muscle, which separates the sinus venosus and atrium. It starts in the upper septum and passes anterior to the orifice of the SVC and then to the right of the orifice of the IVC, where it is continuous with the IVC valve. The sulcus terminalis is an outer surface groove on the lateral wall, between the orifices of the SVC and IVC. Corresponding to the crista terminalis. The crista terminalis, the valves of the IVC and the coronary sinus, represent the remains of the two venous valves which guard the opening of the sinus venosus into the right atrium in the embryo before the two merge to form the adult right atrium. The auricle or atrial appendage is a small triangular muscular pouch which projects towards the left atrium and overlaps the root of the aorta. Z:\Manuals\A & P manual.doc 3 Created by ButlerL, BouncirG, Burnett G, Created on 16/01/2004, Edited on 19/07/2004 Pectinate muscles are roughly parallel ridges of muscle which extend from the crista terminalis and extend into the atrial appendage. The fossa ovalis is an oval depression in the lower part of the intra atrial septum above and to the left of the IVC. It is the remnants of the foramen ovale in the foetus which allows IVC blood to pass into the left atrium. The limbus fossa ovalis is a ridge derived from the free edge of the septum secundum which surrounds the fossa ovalis depression. The IVC opening is directed towards the fossa ovalis and the IVC valve directs blood towards the fossa. The opening of the SVC lies in a more anterior plane and faces the right AV orifice. The intervenous tubercle is a small projection on the posterior wall just below the SVC which directs blood from the SVC to the tricuspid valve in the foetus. This provides separation of the IVC and SVC streams of blood in the foetus. The anterior cardiac vein orifice opens into the right atrium on its anterior wall. This drains much of right coronary blood. Foramen venarium minimum are the orifices of fine veins which return small amounts of blood from the heart muscle, are irregularly scattered and difficult to identify. Z:\Manuals\A & P manual.doc 4 Created by ButlerL, BouncirG, Burnett G, Created on 16/01/2004, Edited on 19/07/2004 LEFT ATRIUM Is smaller than the right atrium with slightly thicker walls. It is cuboidal in shape and lies posterior to the right atrium. Anterior and to the left are the aorta and concealed pulmonary trunk. The cavity is largely smooth walled and is formed from the primitive pulmonary vein which is incorporate during its development. Initially a single common pulmonary vein opens into the primitive left atrium, but as the atrium expands parts of the vein are incorporated into the wall. The only part derived from the primitive atrium is the auricle. Two pulmonary veins enter each side, often the two left ones have a common opening. The auricle or appendage is a small conical pouch which projects forward from its upper left corner overlapping the pulmonary trunk. It is longer and narrower than the right one with margins, which are more deeply indented, with a constriction at its opening with the left atrium. Pectinate muscles are fewer than the right atrium and are confined to the inner surface of the auricle. The atrial septum has an oval impression bounded by a crescentic ring. This corresponds to the fossa ovalis of the right atrium. Foramina venarium minima are minute venous openings which return blood from the heart muscle. LJR.ISH.001.01 Z:\Manuals\A & P manual.doc 5 Created by ButlerL, BouncirG, Burnett G, Created on 16/01/2004, Edited on 19/07/2004 STRUCTURE OF THE HEART The Right Ventricle Anterior is the pericardium and sternum. Inferior is the diaphragm. To the left and posterior the ventricular septum bulges into the right ventricle. It is crescent shaped in cross section and consists of two parts, the inflow and outflow portions. The inflow portion has rough walls with irregular muscle ridges, the trabeculae carnae. The outflow portion is the anetrosuperior smooth walled infundibulum (funnel) leading to the pulmonary valve. Separating the tricuspid and pulmonary orifices is a thick muscular ridge, the supraventricular crest. The infundibulum represents a persistent part of the bulbous cordis of the foetus which has been incorporated into the right ventricle. It provides support for the pulmonary valve during diastole. The trabeculae carnae are rounded or irregular muscle columns projecting from the whole surface of the RV except the infundibulum. They are of three kinds: 1. ridges 2. fixed at their ends and free in the centre 3. continuous at the base with the ventricular wall, apices projecting into the cavity. The third type are the papillary muscles to which are attached the cordae tendinae, which fan out towards the tricuspid valve. The trabeculated inflow wall may help to slow inflow of blood during diastole and to increase contraction efficiency while the smooth walls of the outflow tract may help to increase velocity of ejecting blood. The Tricuspid Valve Three thin, roughly triangular shaped cusps, the anterior, posterior and septal make up the tricuspid valve. The cusps are not completely separated, the commisures not reaching the annulus. The valve leaflets are considered as a continuous curtain arising from or near the annulus with three grades of indentation dividing it into definable parts. The deepest indentations are the three commisures separating the main leaflets.