609
CHAPTER FIFTEEN
Cardiovascular System
that blood flow to part of his myocardium had
been obstructed, producing oxygen deF
ciency.
The attack began as severe, crushing chest pain,
shortness of breath, and sweating. Paramedics
stabilized Dave’s condition and transported him
to a hospital. There, a cardiologist concluded
from an ECG that Dave’s heart attack was caused
by a blood clot obstructing a coronary artery
(occlusive coronary thrombosis). The cardiologist
intravenously administered a thrombolytic (“clot-
busting”) drug.
A repeat ECG a few hours later showed that
the blood vessel remained partially obstructed,
so the cardiologist ordered a
coronary angiogram.
In this X-ray procedure, conducted in a cardiac
catheterization laboratory, a thin plastic catheter
was passed through a guiding sheath inserted
into the femoral artery of Dave’s right inguinal
area. ±rom there, the catheter was pushed into
the aorta until it reached the region of the open-
ing to the left coronary artery, and then near the
opening to the right coronary artery.
X-ray f
uoroscopy
monitored the progress of
the catheter. Each time the catheter was in proper
position, a radiopaque dye (contrast medium)
was released from its distal end into the blood.
X-ray images that revealed the path of the dye
as it entered a coronary artery and its branches
were recorded on videotape and on motion-
picture film, later analyzed frame by frame.
A single severe narrowing was discovered near
the origin of Dave’s left anterior descending
artery. The cardiologist decided to perform
percu-
taneous transluminal coronary angioplasty
(PTCA)
to enlarge the opening (lumen) of that vessel.
D
ave R., a fifty-two-year-old overweight
accountant, had been having occasional
chest pains for several months. The mild
pain occurred during his usual weekend tennis
match, and he attributed it to indigestion. The
discomfort almost always diminished after the
game, but recently, the pain seemed more severe
and prolonged. Dave asked his physician about
the problem.
The physician explained that Dave was prob-
ably experiencing
angina pectoris,
a symptom of
coronary artery disease
(CAD), and suggested that
he undergo an
exercise stress test.
Dave walked
on a treadmill, increasing speed and incline
while he exercised. An ECG was recorded and
his blood pressure monitored. Near the end of
the test, when Dave’s heart reached the desired
rate, a small amount of radioactive thallium-201
was injected into a vein. A
scintillation counter
scanned Dave’s heart to determine if branches
of his coronary arteries carried the blood marked
with the thallium uniformly throughout the myo-
cardium (see F
g. 15.14).
The test revealed that Dave was developing
CAD. In addition, he had hypertension and high
serum cholesterol. The physician advised Dave to
stop smoking; to reduce his intake of foods high
in saturated fats, cholesterol, refined carbohy-
drates, and sodium; and to exercise regularly. He
was given medications to lower his blood pres-
sure and to relieve the pain of angina. The doctor
also cautioned Dave to avoid stressful situations
and to lose weight.
Six months later, despite following medi-
cal advice, Dave su²
ered a heart attack—a sign
The PTCA was performed by passing another
plastic catheter through the guiding sheath
used for the angiogram. This second tube had a
tiny deflated balloon at its tip. The balloon was
placed in the region of the arterial narrowing and
in³
ated for a short time under high pressure. The
in³
ating balloon compressed the atherosclerotic
plaque (atheroma) obstructing the arterial wall
and stretched the blood vessel wall, widening its
lumen (recanalization). Blood flow to the myo-
cardial tissue downstream from the obstruction
immediately improved.
About 50% of the time, a vessel opened
with PTCA becomes occluded again, because the
underlying disease persists. To prevent this reste-
nosis, the doctor inserted a
coronary stent,
which
is an expandable tube or coil that holds the vessel
wall open. The cardiologist had two other options
that have a slightly higher risk of causing damage.
She might have vaporized the plaque obstructing
the vessel with an excimer laser pulse delivered
along optical F
bers threaded through the cath-
eter. Or, she could have performed atherectomy,
in which a cutting device attached to the balloon
inserted into the catheter spins, removing plaque
by withdrawing it on the catheter tip.
Should the coronary stent fail, or an obstruc-
tion block another heart vessel, Dave might beneF
t
from
coronary bypass surgery.
A portion of his inter-
nal mammary artery inside his chest wall or his great
saphenous vein would be removed and sutured
(with the vein reversed to allow blood ³
ow through
the valves) between the aorta and the blocked
coronary artery at a point beyond the obstruction,
restoring circulation through the heart.
15.8
CLINICAL APPLICATION
Coronary Artery Disease
completely healthy cardiovascular systems, they discovered
that cardiac output at rest is maintained as a person ages. It
does decline during exercise for some people, however.
The heart may normally shrink slightly with age, but
disease may enlarge it. The proportion of the heart that is
cardiac muscle declines with age, even in a healthy person,
because cardiac muscle cells do not divide. Lipofuscin pig-
ments become especially prominent in these cells. Fibrous
connective tissue and adipose tissue ±
ll in the spaces left by
the waning population of cardiac muscle cells, thickening
the endocardium. Adipose cells may also accumulate in the
ventricle walls and the septum between them. The left ven-
tricular wall may be up to 25% thicker at age eighty than it
was at age thirty.
of disease of the heart and blood vessels increases expo-
nentially with age. About 60% of men over age sixty have
at least one narrowed coronary artery; the same is true for
women over age eighty.
Assessing cardiac output over a lifetime vividly illus-
trates how cardiovascular disease prevalence can interfere
with studying the changes associated with normal aging.
Recall that cardiac output is the ability of the heart to meet
the body’s oxygen requirements and is calculated as the
heart rate in beats per minute multiplied by the stroke vol-
ume in milliliters per beat. For many years, studies indicated
that cardiac output declines with age, but when researchers
began to screen participants for hidden heart disease with
treadmill stress tests, then evaluated only individuals with
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