Page 1666 - Saunders Comprehensive Review For NCLEX-RN

septum; and the left bundle branch, which extends
into the left ventricle.
3. The right and left bundle branches terminate in the
Purkinje fibers.
H. Purkinje fibers
1. Purkinje fibers are a diffuse network of conducting
strands located beneath the ventricular endocardium.
2. These fibers spread the wave of depolarization
through the ventricles.
3. Purkinje fibers can act as the pacemaker with a rate
between 20 and 40 beats per minute when higher
pacemakers (such as the SA and AV nodes) fail.

I. Coronary arteries (Fig. 52-1)

1. The right main coronary artery supplies the right
atrium and ventricle, the inferior portion of the left
ventricle, the posterior septal wall, and the SA and
AV nodes.
2. The left main coronary artery consists of 2 major
branches, the left anterior descending (LAD) and the
circumflex arteries.
3. The LAD artery supplies blood to the anterior wall of
the left ventricle, the anterior ventricular septum, and
the apex of the left ventricle.
4. The circumflex artery supplies blood to the left atrium
and the lateral and posterior surfaces of the left
ventricle.

The coronary arteries supply the capillaries of the myocardium

with blood. If blockage occurs in these arteries, the client is at risk for
myocardial infarction (MI).
J. Heart sounds
1. The first heart sound (S ) is heard as the
1
atrioventricular valves close and is heard loudest at
the apex of the heart.
2. The second heart sound (S ) is heard when the
2
semilunar valves close and is heard loudest at the
base of the heart.
3. A third heart sound (S ) may be heard if ventricular
3
wall compliance is decreased and structures in the
ventricular wall vibrate; this can occur in conditions
such as heart failure or valvular regurgitation.
However, a third heart sound may be normal in
individuals younger than 30 years.
4. A fourth heart sound (S ) may be heard on atrial
4
systole if resistance to ventricular filling is present;

1666