Heart – Cor
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Heart and blood vessels Heart
The average weight of a human heart is 290–350 g.
The heart is the main organ of the cardiovascular system. It is located behind the sternum in the middle inferior mediastinum. One-third of the heart is positioned to the right of the median plane whilst the other two-thirds are on the left side. The cardiac axis connects the opening of the superior vena cava with the apex of the heart; it directs diagonally, ventrally, and caudally. The heart consists of four chambers separated by septa and valves. From the clinical and functional viewpoint, the heart is divided into the right heart and the left heart. The pericardium is a firm sac composed of two sheets that are separated by 15–50 ml of serous fluid, enabling smooth heart movements. Anteriorly, the heart is positioned in the pericardium freely while posteriorly it is attached by the main vessels entering and leaving the heart.
The location of the heart depends on age, position of the diaphragm, the respiratory movements, the shape of the thorax and body position. In a short and wide thorax with a high position of the diaphragm the heart is positioned more horizontally. In a narrow and long thorax the heart is positioned more longitudinally. Pendulum heart (cor pendulum) is a term for a heart located in a narrow and long thorax; the heart looks like it’s hanging down from the great vessels.
Topography of the heart in the pericardium
• 1 Ventrally: anterior inferior mediastinum and sternum • 2 Dorsally: posterior inferior mediastinum and vertebral column • 3 Laterally: descending phrenic nerves with the pericardiacophrenic vessels and pericardium lining the mediastinal pleura • 4 Cranially: the aortic arch, arising from the heart and heading to the superior mediastinum • 5 Caudally: central tendon of the diaphragm
The auscultation points are also termed Testut’s points. Connecting these points with a line traces the circumference of the projection of the heart onto the thoracic wall.
T1 T2
4
T3
4
3
Viscerosensory innervation of the heart is provided by branches of the phrenic nerves that innervate the pericardium.
T4 T5
1
T6 T7
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5 2
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The pericardiacophrenic arteries accompanying the phrenic nerves provide the arterial supply of the pericardium.
T8 T9 T 10
Anterior view of the heart in the pericardium
Projection of the heart onto the anterior thoracic wall
T 11 T 12 Sagittal section of the mediastinum
• The projection of the heart on the anterior
throacic wall is determined by four points: – 2nd intercostal space on the right, 1 cm lateral to the sternum – 5th intercostal space on the right near the linea sternalis – 5th intercostal space on the left medial to the midclavicular line corresponds to the projection of the apex of the heart – 2nd intercostal space on the left side 2 cm lateral to the sternum
Auscultation sites of the heart valves
A
Clinical notes
P
Cardiac tamponade is a pathological disorder in which fluid accumulates in the pericardial cavity causing the heart to be unable to adequately distend during diastole. The pericardial cavity can expand to contain 1000 ml of fluid. If the increase of fluid occurs slowly over a long period time there may be no clinical manifestations. An acute tamponade is caused by a sudden increase of fluid, by approximately tens of millilitres (max. 200 ml) and is a medical emergency. This situation may occur due to rupture of free myocardial wall over a postischemic scar or as a result of rupture or dissection of the aorta.
T M
Projection of the heart and auscultation sites of the heart valves
• A – Aortic valve: 2 right intercostal space close to the sternum • P – Pulmonary valve: 2 left intercostal space close to the sternum • T – Tricuspid valve: 5 right or left intercostal space close to the sternum • M – Mitral valve: 5 left intercostal space just medial to the midclavicular line nd
nd
th
th
Pericardium 1 The pericardium forms several structures where 3 its parietal layer and visceral layers fuse: 2 1 Porta arteriarum – a cranially positioned opening for 4 the aorta and pulmonary trunk arising from the heart 2 Porta venarum – a caudally positioned opening for the two caval veins and the four pulmonary veins entering the heart 3 Transverse pericardial sinus (sinus transversus pericardii) – a space on the posterior surface of the pericardium between porta arteriarum and porta venarum 4 Oblique pericardial sinus (sinus obliquus pericardii) Anterior view of the posterior part of the pericadrium with the heart removed – a space beneath the area of the porta venarum
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Pericardiocentesis is a surgical procedure in which fluid is removed from the pericardial cavity. It is performed with a special needle that is inserted between the xiphoid process and the left costal margin within the infrasternal angle under ultrasound control. It is also performed, but less commonly, in the inferior interpleural area in the 5th left intercostal space near the left sternal border.