mended LDL-C level depends on risk factors for
CARDIOVASCULAR DISEASE(CVD). The higher the car-
diovascular risk, the lower the recommended
LDL-C level.
- Treatment may use lifestyle (diet and exercise)
modification alone, which is effective for meet-
ing LDL-C target levels for many people whose
LDL-C blood values are 100–130 milligrams per
deciliter (mg/dL) and who have no more than
one additional CVD risk factor. - For people who already have some form of
CVD or who have two or more additional risk
factors for CVD, treatment combines lifestyle
with lipid-lowering medications. - People who have very high CVD risk and very
high LDL-C values may take two or more med-
ications to bring their LDL-C blood levels to a
healthier range.
Some cardiologists advocate driving LDL-C lev-
els even lower, to 70 mg/dL, in people who have
severe risk for HEART ATTACKor STROKE, such as
those who have already had such a cardiovascular
crisis and have numerous risk factors for cardio-
vascular disease. For most people, reaching the
LDL-C target means a decrease of 30 to 40 per-
cent.
See also CARDIOVASCULAR DISEASE PREVENTION;
CHOLESTEROL, DIETARY; CHOLESTEROL, ENDOGENOUS;
GARLIC; HYPERLIPIDEMIA; LIFESTYLE AND CARDIOVASCU-
LAR HEALTH; MEDICATIONS TO TREAT CARDIOVASCULAR
DISEASE; TRIGLYCERIDE BLOOD LEVEL; TRIGLYCERIDES,
DIETARY.
circle of Willis A looped network (anastamosis)
of arteries at the base of the BRAIN. Branches of the
internal carotid arteries form the front of the circle
and branches of the posterior cerebral arteries
form the back of the circle, with smaller arteries,
collectively called the communicating arteries,
branching from them. The circle of Willis is a
unique vascular structure in the body that pro-
vides an extended safety net of redundancy for
the brain’s BLOODsupply; the closest analogous
configuration is that of the CORONARY ARTERIES
which supply the HEART. Even if damage occurs to
one or two of the circle of Willis’s anastomosed
arteries, blood flow to the brain continues. The
base of the skull protects this arterial network. The
circle of Willis, because of its complexity, varies
anatomically among individuals and is a common
site for congenital vascular anomalies (malforma-
tions of the blood vessels).
For further discussion of the circle of Willis
within the context of cardiovascular structure and
function, please see the overview section “The
Cardiovascular System.”
See also ARTERIOVENOUS MALFORMATION (AV M);
ARTERY.congenital heart disease HEART conditions,
including structural anomalies of the heart, that
are present from birth. Some forms of congenital
heart disease are mild to moderate and require
minimal or one-time intervention to correct. Con-
genital heart malformations are among the most
common BIRTH DEFECTS in the United States.
Though still the leading cause of infant death due
to birth defects, congenital heart malformations
no longer mean certain death. Beginning in the
1950s pediatric cardiology pioneers Alfred Blalock
(1899–1964), Helen Taussig (1898–1986), and
Vivien Thomas (1910–1985) established many of
the operations and surgical techniques that
remain in use today to create functional BLOOD
flow through malformed hearts. Advances in CAR-
DIOPULMONARY BYPASSand refinements in surgical
techniques have made relatively normal lives pos-
sible for more than a million children with heart
defects born since 1970.
Structural deformities that affect the heart’s
ability to circulate oxygenated blood result in
inadequate oxygen reaching the body’s tissues and
cause CYANOSIS, a bluish tint to the lips, nail beds,
mucous membranes, and SKIN. Doctors collectively
refer to these conditions as cyanotic heart disease
(sometimes called blue baby syndrome). These
conditions are nearly always apparent within 48
hours of birth and typically require fairly immedi-
ate intervention (usually surgery). Other forms of
congenital heart disease, such as LONG QT SYNDROME
(LQTS) and hypertrophic CARDIOMYOPATHY, may not
manifest until late childhood or adulthood.
Heart defects may occur in isolation or in com-
bination with GENETIC DISORDERSsuch as DOWN SYN-
DROME(trisomy 21) and MARFAN SYNDROME. Heart
abnormalities often occur in association withcongenital heart disease 37