HUMAN BIOLOGY

CirCulation: the heart and blood vessels 135

the heart atria, reducing normal blood flow into the ven-

tricles. ventricular fibrillation is by far the most danger-

ous arrythmia (Figure 7.21B). In parts of the ventricles, the

heart muscle con tracts haphazardly, so blood isn’t pumped

normally. This is what happens in sudden cardiac arrest

(SCA), as described in the chapter introduction.

inflammation is a factor in

cardiovascular disease

Interestingly, more than half of people who suffer heart

attacks don’t have major risk factors. Scientists study-

ing this puzzle have focused on inflammation, a defense

response discussed in Chapter 9. Infections can trigger

inflammation, which in turn causes the liver to make

C-reactive protein, which also is implicated in heart dis-

ease. This link is why infection-related inflammation and

C-reactive protein are listed in Table 7.2. Homocysteine,

an amino acid, is released as certain proteins are broken

down. Too much of it in the blood also may cause damage

that is a first step in atherosclerosis.

when blood-starved heart muscle no longer receives
enough oxygen. Typical warning signs in men include pain
or a sensation of squeezing behind the breast bone, pain or
numbness radiating down the left arm, sweating, and nau-
sea. A woman who is having a heart attack may have simi-
lar signs, but women more often experience neck and back
pain, fatigue, a vague sense of indigestion, a fast heartbeat,
shortness of breath, and low blood pressure. In both males
and females, risk factors include atherosclerosis, a circulat-
ing embolus, and high blood pressure. In heart failure
(HF), the heart is weakened and cannot pump enough
blood to meet the body’s needs. For patients with HF, even
walking can be difficult.

arrhythmias are abnormal heart rhythms

An electrocardiogram, or ECG, is a recording of the
electrical activity of the heart muscle during the cardiac
cycle (Figure 7.21A). ECGs reveal arrhythmias, or irregu-
lar heart rhythms. Some arrhythmias are abnormal, oth-
ers are not. For example, endurance athletes may have a
below-average resting cardiac rate, or bradycardia, which
is an adaptation to regular strenuous exercise. A cardiac
rate above 100 beats per minute, called tachycardia, occurs
normally during exercise or stress ful situations. Serious
tachycardia can be triggered by drugs (including caffeine,
nicotine, alcohol, and cocaine) and exces sive thyroid hor-
mones, among other factors.
In the arrhythmia called atrial fibrillation (AFib), rapid,
disorganized electrical impulses hamper contraction of

1. Inherited predisposition


2. Elevated blood lipids (cholesterol, trans fats)


3. Hypertension


4. Obesity


5. Smoking


6. Lack of exercise


7. Age 50+


8. Inflammation due to infections


9. High blood levels of C-reactive protein


10. Elevated blood levels of homocysteine

Table 7.2 Major Risk Factors for Cardiovascular Disease

F i g u r e 7. 2 1 Animated! An ECG can reveal abnormal heart

activity. A ECG of a normal heartbeat. The P wave is generated

by electrical signals from the SA node that stimulate contraction

of the atria. As the stimulus moves over the ventricles, it is

recorded as the QRS wave complex. The T wave marks the

brief period when the ventricles are resting. B A recording of

ventricular fibrillation.

© Cengage Learning

ventricular

B fibrillation

0.8

A

R

P T

QS

0 0.2 0.4 0.6

time (seconds)

© Alexander Raths/Shutterstock.com

Figure 7.20 Bypass surgery and balloon angioplasty are

common treaments for clogged coronary arteries.

plaque flattened by

balloon angioplasty

stent (metal mesh) placed

to keep artery open

B

From Frances Sienkiewicz Sizer; Eleanor Noss Whitney,

Nutrition:

Concepts and Controversies

,

© 2002 Cengage Learning

A

vein from leg

used to bypass

blockage

blocked

coronary artery

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