The thoracic cavity is divided into the right and left pleural cavities, and, centrally, the mediastinum (situated between the sternum anteriorly and the vertebral column posteriorly). For descriptive purposes, the mediastinum is divided by a horizontal plane through the manubriosternal joint. This crosses the lower border of the body of the fourth thoracic vertebra posteriorly. The superior mediastinum containing the great vessels, lies above this plane. The cavity below the plane contains the heart, within its pericardial sac. The potential space in front of the heart is the anterior mediastinum and the posterior mediastinum lies behind the heart: it contains the tracheal bifurcation, the hila of the lungs, the esophagus and the descending thoracic aorta.

The heart is a muscular pump that maintains blood flow through the systemic and pulmonary circulations. It is about the size of a fist. The complex coiling and division of the primitive cardiac tube, produces four cavities, two atria and two ventricles, separated by interatrial and interventricular septa that divide the heart into right and left sides: the axis of the heart comes to lie downwards and to the left.

The right atrium receives deoxygenated blood from the upper and lower halves of the body through the superior and inferior vena cavae, and from the cardiac muscle via the coronary sinus, and pumps it through the tricuspid valve to the right ventricle. This in turn pumps the blood through the pulmonary valve to the pulmonary trunk and pulmonary arteries, into the lungs. Oxygenated blood is returned to the left atrium via four pulmonary veins and is pumped through the mitral valve to the left ventricle, and from there, through the aortic valve into the aorta to be distributed throughout the body.

The right atrium receives deoxygenated blood from the upper and lower halves of the body through the superior and inferior vena cavae, and from the cardiac muscle via the coronary sinus, and pumps it through the tricuspid valve to the right ventricle. This in turn pumps the blood through the pulmonary valve to the pulmonary trunk and pulmonary arteries, into the lungs. Oxygenated blood is returned to the left atrium via four pulmonary veins and is pumped through the mitral valve to the left ventricle, and from there, through the aortic valve into the aorta to be distributed throughout the body.

The synchronous activity of the two atria and the two ventricles, and the sequential contraction of the atria followed by the ventricles, is maintained by cyclical electrical activity passing through the conducting system of the heart. The valves ensure unidirectional flow without regurgitation.

The base of the heart faces posteriorly and is formed of the left atrium. The pulmonary veins enter at each side forming a rough rectangular shape that lies in front of the tracheal bifurcation (carina) and the esophagus. The right atrium, and superior and inferior venae cavae form the right border and side of the heart, the apex projects to the left and is formed of the ventricles. The left ventricle is larger and forms most of the apex and the inferior and posterior surfaces. The right ventricle forms the anterior and most of the superior surface of the heart. The pulmonary trunk and aorta leave the heart superiorly to the right enclosed in a common pericardial sheath.

The pericardial sac is attached around the base and right side of the heart around the great vessels, this leaves the rest of the heart free for its pump action. Figure 35 shows the anterior surface marking of the cavities, valves and great vessels; the lower border of the heart is at the level of the xiphisternal joint. The heart and great vessels are well demonstrated with CT transverse sections of the thorax (figure 36a–c). The heart sounds, produced by opening and closing of the valves, radiate to specific sites on the chest wall, as do sounds of abnormalities of the valves and heart muscle.

  1. Right common carotid artery
  2. Left common carotid artery
  3. Right subclavian artery
  4. Left subclavian artery
  5. Brachiocephalic (innominate) artery
  6. Brachiocephalic vein, left
  7. Brachiocephalic vein, right
  8. Superior vena cava
  9. Aortic Arch
  10. Left pulmonary artery
  11. Ascending aorta
  12. Pulmonary trunk
  13. Pulmonary valve
  14. Aortic valve
  15. Mitral valve
  16. Right atrium
  17. Left ventricle
  18. Tricuspid valve
  19. Right ventricle
  20. Inferior vena cava

CT through T3

  1. Manubrium sternum
  2. Brachiocephalic (innominate) artery
  3. Left brachiocephalic vein
  4. Right brachiocephalic vein
  5. Left common carotid artery
  6. Trachea
  7. Right subclavian artery
  8. Right lung
  9. Esophagus
  10. Vertebral body T3
  • Calcified structure (probably related to sternoclavicular joint)

 

CT through T5

  1. Right atrium
  2. Right ventricle
  3. Right pulmonary vein
  4. Left atrium
  5. Left pulmonary vein
  6. Esophagus
  7. Descending thoracicaorta
  8. Vertebral body T5

CT through T8

  1. Xiphisternum
  2. Right ventricle
  3. Left ventricle
  4. Esophagus
  5. Descending thoracic aorta
  6. Vertebral body T8

The heart is subject to a wide variety of congenital defects, some of which are incompatible with life. Those encountered in clinical practice include atrial and ventricular septal defects, patent ductus arteriosus, various components of Fallot’s tetralogy and coarctation of the aorta. These conditions give rise to characteristic changes of heart sounds with additional sounds, murmurs and alteration in rhythm. They may produce cardiac failure with the symptoms of dyspnea, palpitations and peripheral edema. In some cardiac abnormalities there is a mixing of venous and arterial blood producing cyanosis.

The cardiac valves may be congenitally abnormal or damaged after rheumatic fever. These abnormalities may be detected on clinical examination as well as by tests of cardiac function. Ischemic damage to the myocardium, due to coronary artery disease, gives rise to angina (cardiac pain on exercise), abnormal cardiac rhythms and cardiac failure.

The clinical assessment of cardiac function is an essential part of the general as well as the cardiac examination. The pulse provides information on cardiac output. Enlargement of the heart and signs of excess fluid in the tissues and body cavities, indicate pump failure, and the heart sounds provide evidence of valvular and other cardiac abnormalities. The examination of the chest includes both the heart and lungs, but in this section the heart is considered separately. The pulse provides an indication of cardiac activity, but examination of the vascular system includes all peripheral pulses and the venous and lymphatic systems. These are usually examined separately and this practice is followed below.

The cardiac history and examination (page 407) play a key role in assessment, as investigations only record function at a specific moment in time. In the cardiac history, consider chest pain, dyspnea, syncope, palpitations, fatigue, hemoptysis and edema. Check the past history for rheumatic fever, bacterial endocarditis, congenital valvular anomalies and tissue disorders, such as Marfan’s syndrome and Ehlers- Danlos syndrome that may lead to heart valve abnormalities. Note previous cardiac problems and operations, and question for cardiac risk factors, such as diabetes, hypercholesterolemia, hypertension, smoking and a family history of coronary artery disease.

Assessment of cardiac function is an important preoperative measure and valuable in long term follow-up. A number of grading systems have been developed but that of the New York Heart Association (NYHA) is a useful monitor:

NYHA 1: No limitation of ordinary physical activity

NYHA 2: Ordinary physical activity causes discomfort

NYHA 3: Moderate to great limitation of ordinary physical activity

NYHA 4: Unable to perform any physical activity without discomfort