Page 434 - Textbook of Pathology, 6th Edition

418 fibres transmit impulses from the AV node to the ventricular adjacent half of the posterior wall of the left ventricle and
walls. the posterior third of the interventricular septum.
The pericardium consists of a closely apposed layer, There are 3 anatomic patterns of distribution of the
visceral pericardium or epicardium, and an outer fibrous sac, coronary blood supply, depending upon which of the
the parietal pericardium. The two layers enclose a narrow coronary arteries crosses the crux. Crux is the region on the
pericardial cavity which is lined by mesothelial cells and posterior surface of the heart where all the four cardiac
normally contains 10-30 ml of clear, watery serous fluid. This chambers and the interatrial and interventricular septa meet.
fluid functions as lubricant and shock absorbant to the heart. These patterns are as under:
The endocardium is the smooth shiny inner lining of the Right coronary artery preponderance is the most
myocardium that covers all the cardiac chambers, the cardiac common pattern. In this, right coronary artery supplies blood
valves, the chordae tendineae and the papillary muscles. It to the whole of right ventricle, the posterior half of the
is lined by endothelium with connective tissue and elastic interventricular septum and a part of the posterior wall of
fibres in its deeper part. the left ventricle by crossing the crux.
The valve cusps and semilunar leaflets are delicate and
Balanced cardiac circulation is the next most frequent
translucent structures. The valves are strengthened by pattern. In this, the right and left ventricles receive blood
collagen and elastic tissue and covered by a layer of supply entirely from right and left coronary arteries
endothelium (valvular endocardium).
respectively. The posterior part of the interventricular septum
MYOCARDIAL BLOOD SUPPLY. The cardiac muscle, in is supplied by a branch of the right coronary while the
order to function properly, must receive adequate supply of anterior part is supplied by a branch of the left coronary
oxygen and nutrients. Blood is transported to myocardial artery.
cells by the coronary arteries which originate immediately Left coronary preponderance is the least frequent pattern.
above the aortic semilunar valve. Most of blood flow to the In this, the left coronary artery supplies blood to the entire
myocardium occurs during diastole. There are three major left ventricle, whole of interventricular septum and also
coronary trunks, each supplying blood to specific segments supplies blood to a part of the posterior wall of the right
of the heart (Fig. 16.2): ventricle by crossing the crux.
1. The anterior descending branch of the left coronary Coronary veins run parallel to the major coronary arteries
artery supplies most of the apex of the heart, the anterior to collect blood after the cellular needs of the heart are met.
surface of the left ventricle, the adjacent third of the anterior Subsequently, these veins drain into the coronary sinus.
SECTION III
wall of the right ventricle, and the anterior two-third of the
interventricular septum. PATTERNS AND CLASSIFICATION OF
2. The circumflex branch of the left coronary artery HEART DISEASES
supplies the left atrium and a small portion of the lateral
aspect of the left ventricle. For the purpose of pathologic discussion of heart diseases,
3. The right coronary artery supplies the right atrium, the they are categorised on the basis of anatomic region involved
remainder of the anterior surface of the right ventricle, the and the functional impairment. Accordingly, topics on heart
diseases are discussed in this chapter under the following
headings:
1. Heart failure
2. Congenital heart diseases
Systemic Pathology
3. Ischaemic heart disease
4. Hypertensive heart disease
5. Cor pulmonale
6. Rheumatic fever and rheumatic heart disease
7. Non-rheumatic endocarditis
8. Valvular diseases and deformities
9. Myocardial disease
10. Pericardial disease
11. Tumours of the heart
12. Pathology of cardiovascular interventions.
It may be mentioned here that pattern of heart diseases
in developing and developed countries is distinct due to
difference in living standards. In children, valvular diseases
are common all over the world, but in developing countries
including India, infections, particularly rheumatic valvular
disease, is the dominant cause compared to congenital
etiology in affluent countries. On the other hand, ischaemic
heart disease and hypertensive cardiomyopathy are the
Figure 16.2 Distribution of blood supply to the heart. major heart diseases in adults in western populations.