Cardiac Anatomy: Heart part 1 PDF

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Paul Tierney; 02/02/12

Heart 1 (Pericardium, Surfaces and Blood Supply) The heart is one of the most important organs in the body, primarily because its failure is a significant cause of human mortality It is the self-adjusting pump in the closed circulation of the cardiovascular system In an adult, it is roughly 12cm in length, 8-9cm in breath at it’s broadest, and 6cm in thickness It is enclosed in the pericardium, into which the heart invaginates (see opposite) Pericardium The pericardium is a conical fibro-serous sac containing the heart, and roots of the great vessels  The lubricated pericardial cavity prevents friction as the heart beats, while the fibrous component attaches the heart to the diaphragm and mediastinum, thereby limiting movement of the heart and great vessels during contraction  The heart lies behind the sternum and the 3rd to 7th right costal cartilages, in the middle mediastinum  Anteriorly, it is separated from the thoracic wall by the lungs and pleura, except behind the lower left portion of the sternum and 4-5th costal cartilages, at the cardiac notch  The thymus in the child lies in front of the upper part of the pericardium  Posteriorly, the pericardium lies on the bronchi, oesophagus, descending aorta and part of the mediastinal surface of the lungs  Laterally, it is covered by the pleurae, and is contiguous with the mediastinal surfaces of the lungs, with the phrenic nerves

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Paul Tierney; 02/02/12

and accompanying pericardiophrenic vessels descending on either side of it Structure -- The pericardium consists of two sacs in intimate contact -- The outer sac is the fibrous pericardium made of irregular connective tissue with abundant collagen -- This is a flask-shaped bag, the neck of which is fused with the adventitial layer of the great vessels, and which is continuous with the pretracheal layer of cervical fascia superiorly -- Inferiorly, the pericardium fuses indivisibly with the central tendon of the diaphragm (both derived from same septum transversarium) -- The inner sac consists of serous pericardium, composed of a single layer of flattened mesothelium, resting on loose connective tissue -- This sac lines the fibrous pericardium and is invaginated by the heart from above and behind, practically obliterating the pericardial cavity (see fig.1) -- This creates the visceral and parietal portions, the former also called the epicardium covering the heart and great vessels -- The pericardial cavity between the visceral and parietal is merely a potential space, normally containing only 10-20 ml of pericardial fluid

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Paul Tierney; 02/02/12

-- Between the two layers of serous pericardium lie two sinuses, transverse and oblique (see fig.4 above) -- The transverse sinus lies above the heart, between the aorta and pulmonary trunk anteriorly and the superior vena cava and pulmonary veins posteriorly -- The oblique sinus lies behind the heart, between the left atrium anteriorly and pareital pericardium posteriorly -- A double layer of serous pericardium separates the two sinuses Blood supply The pericardium is supplied by the internal thoracic artery, its pericardiophrenic and musculophrenic branches, bronchial arteries and twigs from the thoracic aorta Venous blood drains into the azygos system of veins Nerve supply The phrenic nerve supplies the fibrous pericardium The parietal layer of serous pericardium is also supplied by the phrenic nerve, but the visceral layer is insensitive Surfaces  The heart has three surfaces, anterior, posterior and inferior that are usually referred to as sternocostal, diaphragmatic and ‘thebase’  However, nomenclature varies, so any classification can be used as long as it makes sense, justdon’tmixthetwosystems Anterior (sternocostal) surface  This surface is directed forward, upward and to the left and lies behind the sternum and 3-6th costal cartilages  Its lower convex part is formed by the right ventricle, primarily, with a narrow strip of left ventricle on its left border  Its upper part is deeply concave, being

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Paul Tierney; 02/02/12

formed by the atria, and is separated from the lower portion by the vertical atrioventricular groove Inferior (diaphragmatic) surface  This surface is directed downwards and backwards and lies on the central tendon of the diaphragm encroaching slightly onto the left muscular portion  Theventriclesformit,⅓bytheright and⅔bytheleftventricle,separatedby the posterior interventricular artery in its sulcus  That part of the right atrium, which receives the inferior vena cava, intrudes onto the diaphragmatic surface also  Elsewhere, the diaphragmatic surface is separated from the atria by the posterior part of the atrioventricular groove Posterior surface (base)  The base is formed mainly by the left atrium, which receives the four pulmonary veins, with the right atrium encroaching to a small extent  It lies in front of the 5-8th thoracic vertebrae but is separated from them by the oesophagus, aorta and thoracic duct  It is quadrilateral in shape, and related to the bifurcation of the pulmonary trunk above, and the atrioventricular groove below with the coronary sinus running in it  It is delineated on the right by the sulcus terminalis and on the left by the oblique vein of the left atrium  The superior and inferior venae cavae open into its superior and inferior borders respectively  The ascending aorta and pulmonary trunk emerge from the ‘top’oftheheart,butthishasnospecificname

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Paul Tierney; 02/02/12

Borders The heart also has three borders, right, inferior and left -- The right border, made up of the right atrium, is rounded and almost vertical -- It extends from the right third costal cartilage down to the right sixth cartilage -- The inferior border comprises the right ventricle only and is horizontal and sharp, sometimes being called the acute margin -- It extends from the right sixth costal cartilage across to the apex -- The left border is short, full and rounded being formed by the left ventricle, with an addition from the left atrium above -- It extends from the 2nd left costal cartilage, down to the apex, with a convexity to the left -- The apex is directed downward, forward and to the left, and is overlapped by the left lung and pleura -- It is said to lie behind the fifth left intercostal space, 7-9 cm from the mid-sternal line, or more conveniently, just medial to the midclavicular line, but it varies hugely in position Blood supply The arterial supply to the heart is by two coronary arteries, right and left, so called because they and their major branches resemble a crown sitting on the heart,  Of the total coronary artery blood flow approximately 15% is supplied by the right coronary artery and approximately 85% is supplied by the left coronary artery  The relative distribution of these two coronary arteries between the left and right ventricles varies among individuals  These arteries are given off the anterior and left posterior aortic sinuses, at the commencement of the ascending aorta

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Paul Tierney; 02/02/12

Right coronary artery This artery is the smaller of the two coronary arteries and supplies just 15% of the arterial blood to the heart, as it is supplying the less muscular right ventricle  The right coronary artery passes from the anterior aortic sinus, between the infundibulum of the right ventricle and the right auricle, to run inferiorly in the atrioventricular groove  It passes posteriorly in this groove at the inferior border of the heart, to supply both atrium and ventricle  One of the first branches it gives off is the conus artery, which passes upwards and medially on the infundibulum, to supply the origin of the pulmonary trunk, often anastomosing with a similar branch from the left coronary artery  Another high atrial branch is usually the SA nodal artery, which runs posteriorly between the right auricle and aorta to form a vascular ring around the termination of the superior vena cava  It supplies the important SA node in 60% of hearts, the other 40% being supplied by an SA nodal artery from the left coronary artery  At the inferior border of the heart the right

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Paul Tierney; 02/02/12

coronary artery branches off the right marginal artery, which passes down the right margin of the ventricle, or occasionally in front of it  On the diaphragmatic surface the posterior interventricular branch is given off, to pass down the interventricular groove towards the apex  On angiograms the right coronary has a characteristic loop where the posterior interventricular is given off; the AV nodal artery arises here andocclusionoccurshereduetothe‘kink’  The remnant of the right coronary artery anastomoses with the termination of the circumflex branch of the left coronary  Occlusion of the right coronary affects the hearts conduction system predominantly Left coronary artery This is the bigger of the two coronary arteries, as it supplies 85% of the arterial blood to the heart, most importantly to the left ventricle  The left coronary arises from the left posterior aortic sinus and passes forward between the left auricle and infundibulum  After a short course it divides into circumflex and anterior interventricular branches, the circumflex being the continuation  This latter artery continues around the left margin in the atrioventricular groove to the back, giving off ventricular and atrial branches, before anastomosing with the end of the right coronary  In 40%, an SA nodal artery is given off the circumflex artery  An obtuse marginal artery often passes down the left border  The anterior interventricular artery runs down the interventricular groove anteriorly, under the apex, to anastomose with the posterior interventricular on the diaphragmatic surface  Near its origin it also gives off a conus branch, and several ventricular branches further towards the left  One of these is often large and is known as the diagonal artery, but it may arise directly from the left coronary trunk, with the circumflex  The anterior interventricular artery is the cardiac vessel

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Paul Tierney; 02/02/12

most affected by atherosclerosis because of its flow rate, the shear forces exerted on it by left ventricular contraction, and turbulence caused by blood from the large calibre left coronary artery entering the smaller calibre anterior interventricular  This artery also supplies the anterior two thirds of the interventricular septum, which includes the Bundle of His  Occlusion of the left coronary artery affects the hearts pumping ability predominantly Anastomoses and dominance -- In 10%, the right coronary is shorter than usual and the posterior interventricular artery is supplied by a continuation of the circumflex, which will therefore supply the AV node -- Suchheartsaresaidtoshow‘leftdominance’,themore usual variant being balanced dominance (20%)or‘right dominance’ (70%) -- Anastomoses exist between the terminations of the right and left coronary arteries at the arteriolar level, as well as between their interventricular and conus branches -- In occlusion of the coronary arteries, the speed of blockage is important, as with slow progression, healthy arterioles will open up -- With abrupt occlusion or unhealthy arterioles, collateral circulation will not develop to a sufficient degree to sustain the cardiac muscle, and a myocardial infarct will occur -- Potential anastomoses exist between the coronary arteries and pericardial arteries around the roots of the great vessels Coronary veins The veins that drain the heart wall do not have names that correspond to the arteries  These veins consist of the coronary sinus and its five main tributaries; great, middle and small cardiac veins, posterior vein of the left ventricle and the oblique vein of the left atrium; in addition to the

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Paul Tierney; 02/02/12

anterior cardiac veins and venae cordis minimae  The coronary sinus receives most of the cardiac drainage  It lies in the atrioventricular groove posteriorly and its wall is partly muscular  It opens into the posterior wall of the right atrium, to the left of the inferior vena cava opening  The great cardiac vein accompanies the anterior interventricular and circumflex arteries to enter the left end of the sinus  The middle cardiac vein accompanies the posterior interventricular artery opening near the termination of the coronary sinus  The small cardiac vein opens into the distal end of the coronary sinus near its atrial termination  The posterior vein of the left ventricle joins the sinus to the left of the middle cardiac vein  The small oblique vein of the left atrium empties into the left end of the sinus  The anterior cardiac veins are a series which run across the surface of the right ventricle to open into the right atrium  The right marginal vein runs along the inferior cardiac margin to join the small cardiac vein  The venae cordis minimae are very small veins in the walls of all four chambers that open directly into these chambers Lymph supply The lymphatics of the heart drain back along the coronary arteries, emerge from the pericardium with the aorta and pulmonary trunk to empty into the tracheobronchial and brachiocephalic lymph nodes Clinical Angina pectoris/ Myocardial infarction Atherosclerosis/ Coronary arteriography/ Angioplasty PCI (percutaneous coronary interventions) CABG (coronary artery bypass surgery)

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Congenital heart disease (CHD) Pericarditis/ Myocarditis Pericardial tamponade (Beck’striad) Hypertrophic cardiomyopathy (HOCM) Valvular heart disease Dextrocardia with situs inversus

Paul Tierney; 02/02/12...