Cardiovascular Physiology
423
extra CH
2
, is an intermediary in the metabolism of methio-
nine and cysteine. In increased amounts, it exerts several pro-
atherosclerotic effects, including damaging the endothelium
of blood vessels. Folic acid is involved in the metabolism of
homocysteine in a reaction that lowers the plasma concentra-
tion of this amino acid.
Finally, there is the question of alcohol and coronary
artery disease. In many studies, moderate alcohol intake, red
wine in particular, has been shown to reduce the risk of dying
from a heart attack. However, alcohol also increases the chances
of an early death from a variety of other diseases (cancer and
cirrhosis of the liver, for example) and accidents. Because of
these complex health effects, it is now recommended that if
people drink, they should have no more than one drink a day.
A number of different drugs can be used for the pre-
vention and treatment of angina and coronary artery disease.
For example, vasodilator drugs such as
nitroglycerin
(which
is a vasodilator because it is converted in the body to nitric
oxide) help by dilating the coronary arteries and the systemic
arterioles and veins. The arteriolar effect lowers total periph-
eral resistance, thereby lowering arterial blood pressure and
the work the heart must do to eject blood. The venous dila-
tion, by lowering venous pressure, reduces venous return and
thereby the stretch of the ventricle and its oxygen requirement
(a)
Atherosclerotic
plaque
Lipid-rich core
of plaque
Normal blood
vessel wall
Endothelium
Abnormal connective
tissue, smooth muscle,
and macrophages
Inferior
vena cava
Right
coronary
artery
Superior
vena cava
Marginal
artery
Pulmonary
trunk
(divided)
Circumflex
artery
Aortic arch
Left anterior
descending
coronary
artery
Great cardiac
vein
Anterior
interventricular
artery
(c)
(d)
(b)
Figure 12–66
Coronary artery disease and its treatment. (a) Anterior view of the heart showing the major coronary vessels. Inset demonstrates narrowing
due to atherosclerotic plaque. (b) Dye-contrast x-ray angiography performed by injecting radio-opaque dye shows a signifi cant occlusion of the
right coronary artery (arrow). (c) A guide wire is used to position and infl ate a dye-fi lled balloon in the narrow region, and a wire-mesh stent is
inserted. (d) Blood fl ows freely through the formerly narrowed region after the procedure.
(b), (c), and (d) courtesy of Matthew R. Wolff, M.D.
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