Computational Intelligence in Cardiology and Heart Disease Diagnosis - Computational Intelligence in Biomedical Engineering - page 147

for grafting during coronary bypass surgery. The fibrocollagenous tissue also
separates the atrial chamber from the ventricular chamber and therefore, an
impulse from the atrium must pass through the AV node before triggering the
ventricle.

4.2.3 Early Stages of Heart Development
The heart being an integral part of the human body, begins its growth imme-
diately after conception. The adult human heart is the size of a human fist and
after birth grows at approximately the same rate as the fist until adulthood.
However, this linear growth rate is not the same for infants in the womb. In
this section, we look into some detail at how the heart develops from concep-
tion to birth. The interested reader can find further details in McNulty and
Wellman (1996).
After conception, the fetal heart occupies a major portion of the midsection
for the first few weeks. During this stage, the heart size to body size ratio is
nine times greater than in a newborn infant. Initially, the fetal heart lies high
in the chest and later slowly moves down to the chest cavity. The fetal heart's
development can be divided into several phases as follows:

a. Formation of the heart tube

b. Partitioning of the atria

c. Formation of the right atrium and the left atrium

d. Formation of AV canals

e. Formation of the ventricles

f. Partitioning of the outflow tract

The heart begins growing from a portion of the embryo known as the
angiogenic cell cluster located in the cardiogenic plate (see Figure 4.4a). By
the twenty-first day, the angiogenic cell clusters have completely fused into
the heart tube. The newly formed heart tube may be divided into regions (see
Figure 4.4b) beginning with the sinus venosus from the posterior and then the
primitive atria, followed by the primitive ventricle. The primitive atria will
soon fuse to become a single atria, whereas the primitive ventricle expands to
become the left ventricle. The AV sulcus partitions the atria and the primitive
ventricle. This is then followed by the bulbous cordis, which is composed of
the proximal bulbous cordis, conus cordis, and truncus arteriosus. Finally, the
aortic sac and the dorsal aorta are located at the anterior end of the heart tube.
In the beginning, the heart tube grows so fast that it is forced to bend and
twist backward forming the familiar fist shape of the heart. During this time,
the two atria are already partly separated and there is only one big ventricle
(see Figure 4.5). The conus cordis starts enlarging, whereas the truncus arte-
riosus shows some indentation, which indicates where septation (partitioning)