Computational Intelligence in Cardiology and Heart Disease Diagnosis - Computational Intelligence in Biomedical Engineering - page 145

functional unit characteristic is referred to as a functional syncytium , which
means that if an individual muscle cell is stimulated, a contraction in all other
muscle cells will be observed. Owing to differences between the action potential
conduction properties, however, the cardiac muscle contracts at a slower rate
than the skeletal muscle, which is important for natural synchronization of the
heart function, as will be seen later. It has also been found that the amount
of myocardium and the diameter of muscle fibers in the chambers of the heart
differ according to the workload of the specific chamber.
The pericardium sac is composed of two layers separated by a space called
the pericardial cavity: the outer layer is called the parietal pericardium and
the inner layer is the visceral pericardium. The parietal pericardium con-
sists of an outer layer of thick, fibrous connective tissue and an inner serous
layer. The serous layer, consisting largely of mesothelium cells, together with a
small amount of connective tissue forms a simple squamous epithelium, which
secretes approximately 25-35 mL of fluid. The fluid layer lubricates the sur-
faces and provides friction-free movement of the heart within the pericardium
during muscular contractions. The fibrous layer of the parietal pericardium is
attached to the diaphragm and fuses with the outer wall of the great blood
vessels entering and leaving the heart. It functions to provide a strong pro-
tective sac for the heart and also serves to anchor it within the mediastinum.
The visceral pericardium is also known as the epicardium and as such com-
prises the outermost layer of the heart proper. The epicardium forms the
outer covering of the heart and has an external layer of flat mesothelial cells.
These cells lie on a stroma of fibrocollagenous support tissue, which con-
tains elastic fibers as well as the large arteries and venous tributaries carrying
blood from the heart wall. The fibrocollagenous tissue is mainly located at
the heart valves and are composed of a central fibrous body. These extend to
form the valve rings, which support the base of each valve. The valve rings on
the left-hand side of the heart surround the mitral and aortic valves and are
thicker than those on the right-hand side, which surround the tricuspid and
pulmonary valves. A downward extension of the fibrocollagenous tissue of the
aortic valve ring called the septum divides the right and left ventricles into two
chambers. The walls between the atria are divided by the interatrial septum,
whereas the two ventricles are separated by the interventricular septum. The
fibrocollagenous tissue or skeleton is important because it provides attach-
ment for the cardiac muscle and lends support to the atrial and ventricular
valves. Near the front of the interatrial septum is a characteristic depression
known as the fossa ovalis . This was the position of a previous opening known
as the foramen ovale between the two sides of the heart in the fetal stage
of development. This opening shunted blood directly from the right atrium
into the left atrium, thereby diverting blood from the fetus' still developing
lungs.
Each atrium chamber is separated from the ventricle chamber by atrioven-
tricular (AV) valves as shown in Figure 4.3. The AV valves consist of flaps or
fibrous tissue, which project from the heart wall into the opening between the
atrium and the ventricle. These cusps are sheathed by a layer of endothelium