--- module: 077-02 language: en chapter: 77 title: "Thoracic Anatomy, Mediastinum, Heart, Lungs, and Chest Wall" module_title: "Mediastinum, pericardium, heart, coronary circulation, and great vessels" source_sha256: fa6e21a034a8b4ecec519388ffee6eaccadc82635c14568eba86f9421f787721 --- # Mediastinum, heart, and great vessels ## Mediastinal compartments ### Central corridor between pleural cavities #### One lesion can compress several systems ### Sternal angle plane to T4-T5 disc #### Divides superior from inferior ### Inferior split by pericardium ### Superior order: vein, artery, airway, oesophagus ### Anterior: loose tissue, nodes, thymic tissue ### Middle: pericardium, heart, phrenic nerves ### Posterior: aorta, oesophagus, duct, azygos ### Mass sites are tendencies, not rules ## Pericardium ### Fibrous sac on tendon, vessels, sternum ### Serous parietal and visceral layers ### Transverse sinus behind arterial outflow #### Surgical passage around aorta, trunk ### Oblique sinus behind left atrium ### Phrenic anterior, vagus posterior to roots ### Tamponade physiology #### Rapid fluid raises pressure, impairs filling #### Slow fluid stretches sac first #### Right chambers vulnerable in diastole ## External cardiac surfaces ### Apex mainly left ventricle ### Base mainly left atrium, faces back ### Borders #### Right border right atrium #### Left border left ventricle and auricle ### Sternocostal surface mainly right ventricle ### Diaphragmatic surface mainly left ventricle ## Chambers and valves ### Right atrium receives cavae, coronary sinus #### Crista terminalis divides wall #### Fossa ovalis marks foramen ovale ### Right ventricle with moderator band #### Conus arteriosus to pulmonary valve ### Left atrium receives pulmonary veins ### Mitral valve with two papillary groups ### Thick left ventricle for systemic ejection ### Coronaries from right and left aortic sinuses ### Closure by pressure reversal, coaptation #### Papillary muscles prevent prolapse only ### Fibrous skeleton insulates atria ## Coronary territories ### Right coronary in right groove #### Nodal and posterior interventricular branches ### Left coronary splits in two #### Anterior interventricular: anterior septum #### Circumflex in left groove ### Dominance by posterior interventricular origin #### Affects inferior wall and nodal supply ### Functional end arteries #### Acute occlusion infarcts #### Gradual narrowing enlarges collaterals ### Subendocardium perfused mainly in diastole ### Veins drain to coronary sinus ## Conduction and autonomic supply ### Sinoatrial node near caval entry ### Atrioventricular node near coronary sinus ### Bundle crosses skeleton, splits in two #### Right bundle through moderator band #### Left bundle fans along septum ### Nodal supply varies with dominance ### Septal or valve injury impairs conduction ### Sympathetic raises rate and force ### Vagus slows nodal function ### Pain afferents with sympathetics #### Referred chest and medial arm pain ## Great-vessel relations ### Ascending aorta gives coronaries ### Arch over left main bronchus to T4 ### Pulmonary trunk anterior to aorta #### Right artery behind aorta and cava ### Ligamentum arteriosum near left recurrent nerve ### Left brachiocephalic vein crosses anteriorly ### Azygos arches over right root ### Thoracic duct empties at left venous angle #### Injury causes chylothorax ## Mediastinal pathology ### Dissection extends to branches, valve #### Pericardial rupture causes tamponade #### Pleural rupture causes haemothorax ### Aneurysm compresses nerve, airway, veins ### Left atrial enlargement affects oesophagus ### Caval obstruction: collaterals, oedema ### Pneumomediastinum tracks fascial planes ### Auscultation sites are transmission points #### Echocardiography shows real valves