Pericardium & Heart Dr. Zeenat Zaidi

Heart enclosed within the pericardial sac is located in the middle mediastinum

Mediastinum The cavity of thorax is divided into: A median partition, the mediastinum Laterally placed pleurae & lungs Mediastinum is a thick mobile partition, formed by the structures occupying the central part of the thoracic cavity, between the lungs It extends: Superiorly to the thoracic inlet & the root of neck Inferiorly to the diaphragm Anteriorly to the sternum Posteriorly to the twelve thoracic vertebrae

Mediastinum: Divisions Divided, by an imaginary plane passing from the sternal angle anteriorly to the lower border of the body of the 4th thoracic vertebra posteriorly, into: Superior mediastinum Inferior mediastinum The inferior mediastinum is further divided into: Anterior Middle Posterior

Pericardium

Pericardium Double layered fibroserous sac that encloses the heart & the roots of the great vessels Located in the middle mediastinum Posterior to the body of sternum and 2nd-6th costal cartilages Anterior to T5-T8 vertebrae 1-1.5 cm to the right of the sternum 5-7.5 cm to the left of median plane at the level of 5th intercostal space

Pericardium cont’d The strong outer layer, the fibrous pericardium is composed of tough fibrous tissue The inner transparent membrane, the serous pericardium, has two layers: Parietal Visceral

Fibrous Pericardium Tough conical outer fibrous sac, protects heart against sudden overfilling Superiorly: Pierced by aorta, pulmonary trunk, and superior vena cava Becomes fused with the tunica adventitia of these vessels Below: rests on and is fused with the central tendon of the diaphragm

Fibrous Pericardium cont’d Anteriorly attached to the posterior surface of sternum by condensations of connective tissue called the sternopericardial ligaments Posteriorly: Pierced by pulmonary veins and inferior vena cava Becomes fused with the tunica adventitia of these vessels

Serous Pericardium Parietal layer lines the fibrous pericardium and becomes continuous with the visceral layer around the roots of great vessels Visceral layer reflected onto the heart, forms the external layer of the heart wall (epicardium) The two layers are continuous with each other at the base of the large vessels Pericardial cavity lies between the two layers, that contains a thin film of serous fluid which helps in frictionless movement of the heart

Pericardial Sinuses Develop during folding of embryonic heart Transverse sinus: Lies posterior to ascending aorta and pulmonary trunk, anterior to superior vena cava Communicates with the main part of pericardial cavity at its right and left ends Oblique sinus: An inverted U-shaped blind recess lies posterior to the heart extending posterior to the left atrium, can be entered inferiorly Produced by the reflection of pericardium onto the pulmonary veins and inferior vena cava

Blood Supply Arterial Supply: Fibrous pericardium & the parietal layer of the serous pericardium : Mainly supplied by pericardiophrenic and musculophrenic arteries, branches of internal thoracic. Also supplied by pericardial branches of bronchial, esophageal and superior phrenic arteries Visceral layer of the serous pericardium (epicardium) supplied by the branches of the coronary arteries Venous drainage: Veins are tributaries of azygos system. Pericardiophrenic veins also drain into the internal thoracic vein

Nerve Supply The fibrous pericardium and the parietal layer of the serous pericardium are supplied by the phrenic nerves. The visceral layer of the serous pericardium is innervated by sympathetic & parasympathetic fibers through the sympathetic trunks and the vagus nerves respectively

Clinical Notes Pericarditis & pericardial effusion Cardiac temponade Friction rub Pericardiocentesis: A wide-bore needle may be inserted through the left 5th & 6th intercostal space near the sternum (area of cardiac notch). Intracardial injections are also given through this area

Heart To be handled with care….

Heart Hollow muscular organ, acts as a double pump Conical in shape Slightly larger than the clenched fist Lies free within the pericardium Connected superiorly to the large vessels

Heart cont’d Has 4 chambers: two atria superiorly and two ventricles inferiorly, separated from each other by atrioventricular and interventricular grooves Atria act as the receiving chambers and the ventricles as the pumping chambers Right side of the heart contains deoxygenated blood & left side contains oxygenated blood

External Features: Surfaces The heart has: Sternocostal (Anterior) surface Diaphragmatic (Inferior) surface Base (Posterior surface) Apex

Sternocostal Surface Formed mainly by the right atrium and the right ventricle separated by vertical atrioventricular groove The anterior interventricular groove separates the right ventricle from the left ventricle

Diaphragmatic Surface Formed mainly by the right and left ventricles separated by posterior interventricular groove, and a small part of the right atrium, into which the inferior vena cava opens

Base (Posterior Surface) Formed mainly by the left atrium, into which open the 4 pulmonary veins Quadrilateral in shape Lies opposite the apex Faces posteriorly, superiorly and toward the right shoulder

Apex Formed by left ventricle Directed downward, forward and to the left Located posterior to the left 5th intercostal space, 7-9 cm from the median plane and just medial to the left midclavicular line Position varies slightly with the person’s position and the phase of respiration Is the point of maximal pulsation of the heart (the apex beat can be seen as well as palpated)

Borders of the Heart The heart has 4 borders: Right: Formed by the right atrium Left: Formed by the left auricle above and the left ventricle below Inferior: Formed mainly by the right ventricle, and the apex of the left ventricle Superior border is where great vessels enter or leave the heart. Formed by right and left auricles and superior part of right & left ventricle

Surface Projection of the Heart

Blood Supply of the Heart

Arterial Supply Supplied by right & left coronary arteries Coronary arteries arise from the ascending aorta immediately above the aortic valves Coronary arteries and their branches are distributed over the surface of the heart lying within the subepicardial connective tissue

Right Coronary Artery Arises from anterior sinus of ascending aorta Runs between the pulmonary trunk and right auricle Runs in the atrioventricular groove At the inferior border of the heart turns posteriorly in the atrioventricular groove Anastomoses with the left coronary artery in the posterior interventricular groove

Right Coronary Artery: Branches Right conus artery Anterior ventricular branches: 2-3 in number, largest is the marginal branch Posterior ventricular branches, gives a branch to atrioventricular node Posterior interventricular artery Atrial branches, & artery of the sinuatrial node which also supplies atria

Left Coronary Artery Larger than the right Supplies major part of the heart Arises from the left posterior aortic sinus Runs between the pulmonary trunk and left auricle Runs in the atrioventricular groove Divides into anterior interventricular & circumflex branches

Left Coronary Artery: Branches Anterior interventricular artery, gives a small conus artery Circumflex artery, gives: Left marginal Anterior ventricular Posterior ventricular Atrial branches

Variations in Coronary Arteries In 35% of individuals, the sinuatrial artery arises from left coronary artery In most of the individuals (90%), the posterior interventricular artery is a branch of right coronary artery (Right Dominance). In 10% of the individuals, it arises from circumflex branch of left coronary artery (Left Dominance)

Coronary Artery Anastomoses Though anastomoses do exist between the terminal branches of the right and left coronary arteries, but these are not large enough to compensate for any sudden blockage of a large branch. A sudden blockage of the larger branches results in myocardial infarction.

Venous Drainage Most of the blood drains into the right atrium through the coronary sinus, which: Lies in the posterior part of the atrioventricular sulcus Is continuation of the great cardiac vein Opens into the right atrium to the left of the inferior vena cava Tributaries: Small cardiac vein Middle cardiac vein Posterior vein of the left ventricle Oblique vein of the left atrium

Venous Drainage cont’d Anterior cardiac veins drain directly into the right atrium Vena cordis minimi (Thebesian veins) open directly into heart chambers

Thank U & Good Luck