cardiac function, though cardiologists believe
reduced OXYGENATIONbegins with about 50 percent
occlusion. The heart’s ability to develop collateral
circulation, the growth of new arteries, allows
CAD to worsen without overtly affecting cardiac
function.
CAD develops when ATHEROSCLEROTIC PLAQUE
infiltrates the arterial intima, the innermost layer
of the arterial wall, and accumulates into deposits
called atheromas. The atheromas cause the arterial
wall to thicken, reducing its elasticity and thus its
ability to contract and expand in response to blood
flow needs. Atheromas also protrude into the
channel of the artery, reducing the artery’s inte-
rior diameter (lumen) and reducing the volume of
blood the artery can transport. These factors con-
verge to restrict blood flow to the heart, particu-
larly with exertion (such as during physical
exercise), and deprive segments of the heart of
adequate oxygenation. The result is ischemia, or
tissue HYPOXIA. Typically the ischemia eases with
rest, as the heart’s demand for oxygen diminishes.
Symptoms and Diagnostic PathThe key symptom of CAD is ANGINA PECTORIS, a
pressurelike discomfort or pain originating in the
central chest and often radiating up the arm into
the jaw and through the shoulder area to the
back. At this stage, medical or surgical interven-
tions can head off CAD-induced heart attack. For
many people, however, the first indication of CAD
is heart attack, which can occur when an athero-
sclerotic coronary artery ruptures or a blood clot
lodges in a section of a coronary artery where
CAD has narrowed the passageway. The resulting
blockage, or occlusion, interrupts blood flow to a
portion of the heart and the heart tissue dies.
CARDIAC CATHETERIZATIONand ANGIOGRAMprovide
definitive diagnosis. These procedures allow the
cardiologist to visualize the path of blood through
the coronary arteries, highlighting constricted or
blocked areas. Severe CAD also causes ARRHYTHMIA
(disturbance of the heart’s electrical activity),
which a person may experience as PALPITATIONS
and that show up on ELECTROCARDIOGRAM(ECG).
Exercise STRESS TEST, particularly radionuclide test-
ing, reveals the functional limitations resulting
from the CAD. ECHOCARDIOGRAMoften reveals the
dysfunction of the walls of the heart served by dis-
eased coronary arteries, as well as decreased heart
function if there has already been damage, and
with Doppler ULTRASOUNDmay show restrictions in
the flow of blood.
Some cardiologists use MAGNETIC RESONANCE
IMAGING(MRI) to visualize the structure and func-
tion of the coronary arteries and the rest of the
heart. MRI also detects new collateral circulation
(angiogenesis). However, anyone who has a PACE-
MAKER, IMPLANTABLE CARDIOVERTER DEFIBRILLATOR
(ICD), stents, ANEURYSM clips, or other internal
metallic objects cannot undergo MRI. An advan-
tage of MRI is its ability to represent dimensional
cross-sections of the areas of suspected atheroscle-
rotic accumulation. This reveals the extent to
which the CAD has caused the arterial wall to
thicken.
A variation of CT scan, ELECTRON BEAM COMPUTED
TOMOGRAPHY(EBCT) SCAN, can detect calcification
in the arterial walls. Calcification indicates long-
standing accumulations of plaque that have solidi-
fied within the intima, a sign of well-established
CAD that, while perhaps not causing symptoms, is
significant enough to pose the risk of heart attack.
Of equal, and perhaps greater, concern to cardiol-
ogists is the accumulation of soft, unstable athero-
sclerotic plaque, sometimes called vulnerable
atheroma. These soft accumulations appear to
cause continued irritation to the arterial wall, with
resulting clot formation and the risk that the ath-
erosclerotic plaques will rupture, spilling particles
and debris into the blood circulation.Treatment Options and Outlook
Although CORONARY ARTERY BYPASS GRAFT (CABG)
remains the leading treatment for CAD in the
United States, cardiologists are moving toward less
invasive approaches. CABG is an OPEN HEART SUR-
GERYwith numerous risks and complications. A
number of studies in the late 1990s and early
2000s raised questions as to whether CABG pro-
vides a clear benefit over other treatment alterna-
tives such as ANGIOPLASTY, aggressive lipid-lowering
therapy, and significant lifestyle modifications.
Cardiologists now implement the latter two meth-
ods after CABG, and there is increasing evidence
that they are equally effective without CABG.
Angioplasty, a cardiac catheterization procedure in
which a balloon at the tip of a catheter compresses44 The Cardiovascular System