A. General features. The pericardium consists of three layers: a visceral layer of serous pericardium (known histologically as the epicardium); a parietal layer of serous pericardium; and a thick connective tissue layer called the fibrous pericardium. The pericardial cavity, which normally contains a small amount of fluid, lies between the visceral and parietal layers of serous pericardium. The fibrous pericardium fuses superiorly to the adventitia of the great vessels, inferiorly to the central tendon of the diaphragm, and anteriorly to the sternum. The phrenic nerve and pericardiophrenic artery descend through the mediastinum lateral to the fibrous pericardium. They may be injured during surgery to the heart. The transverse sinus is a recess of the pericardial cavity. After the pericardial sac is opened, the surgeon can pass a finger or ligature from one side of the heart to the other through the transverse sinus between the great arteries and pulmonary veins. The oblique sinus is a recess of the pericardial cavity. It ends in a cul-de-sac surrounded by the pulmonary veins. The thoracic portion of the inferior vena cava (IVC) lies within the pericardium. To expose this portion of the IVC, the pericardium must be opened.
1. Cardiac tamponade is the accumulation of fluid within the pericardial cavity. It causes compression of the heart because the fibrous pericardium is inelastic. Clinical findings include: hypotension (blood pressure of 90/40) that does not respond to rehydration; compression of the superior vena cava (SVC), which may cause the veins of the face and neck to engorge with blood; paradoxical pulse (inspiratory lowering of blood pressure by more than 10 mm Hg); spontaneous filling of the syringe when blood is drawn, due to increased venous pressure; and distant heart sounds.
2. Pericardiocentesis is the removal of fluid from the pericardial cavity. It can be approached in two ways.
a. Sternal approach. A needle is inserted at intercostal space 5 or 6 on the left side near the sternum, because the cardiac notch of the left lung leaves the fibrous pericardium exposed at this site. The needle penetrates the following structures: skin superficial fascia -► pectoralis major muscle external intercostal membrane ~~► internal intercostal muscle transverse thoracic muscle fibrous pericardium parietal layer of serous pericardium. The internal thoracic artery, coronary arteries, and pleura may be damaged during this approach.
b. Subxiphoid approach. A needle is inserted at the left infrasternal angle, angled superiorly and posteriorly. The needle penetrates the following structures: skin superficial fascia anterior rectus sheath rectus abdominis muscle transverse abdominis muscle —► fibrous pericardium —► parietal layer of serous pericardium. The diaphragm and liver may be damaged during this approach.
II. SURFACES OF THE HEART
A. Posterior surface (base) consists of the left atrium.
B. Apex consists of the left ventricle at intercostal space 5, along the midclavicular line.
C. Sternal surface consists of the right ventricle. .
D. Diaphragmatic surface consists of the left ventricle.
III. BORDERS OF THE HEART (Figure 5-1)
A. Right border consists of the right atrium and superior vena cava (SVC).
B. Left border consists of the left ventricle, left atrium, pulmonary trunk, and aortic arch.
C. Inferior border consists of the right ventricle.
D. Superior border is formed by the superior vena cava, aorta, and pulmonary trunk.
Figure 5-1. Posteroanterior radiograph of the thorax. Note the various components of the borders of the heart. The costodiaphragmatic recess and the right and left domes of the diaphragm are apparent. (Adapted with permission from Fleckenstein P, Tranum-Jensen J: Anatomy in Diagnostic Imaging. Philadelphia, WB Saunders, 1993, p 202.)
1. Head of first rib
2. Apex of lung
4. Bronchus (longitudinal view)
5. Lung vessel (longitudinal view)
6. Superior caval vein
7. Right atrium
8. Lung vessels
9. Inferior caval vein
10. Costodiaphragmatic sulcus
12. Aortic arch
13. Pulmonary trunk
14. Left auricle
15. Left ventricle
16. Apex of heart
17. Right ventricle
18. Right dome of diaphragm
19. Left dome of diaphragm
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