Ankle-to-Arm Blood Pressure Ratio May Help Define
Cardiovascular Risk
Ankle brachial index is used to indicate the risk of
peripheral artery disease and atherosclerosis
July
8, 2008 A ratio of blood pressure measurements from the ankles and
arms the ankle brachial index may improve the accuracy of predicting
cardiovascular risk, according to a review of previous research that is
reported in the July 9 issue of the Journal of the American Medical
Association.
The ankle brachial index is used to indicate the
risk of peripheral artery disease and atherosclerosis.
The medical community has long sort an accurate
means of identifying patients who are at risk of a heart attack of
stroke from cardiovascular and cerebrovascular events, but have not been
known to have pre-existing cardiovascular disease. The prevention of
these deadly and sudden events is considered a serious public health
challenge.
Various scoring equations to predict those at
increased risk have been developed using cardiovascular risk factors,
including cigarette smoking, blood pressure, total and high-density
lipoprotein cholesterol, and diabetes mellitus, according to the
article.
The Framingham risk score (FRS) is often considered
the reference standard but has limited accuracy, tending to overestimate
risk in low-risk populations and underestimate risk in high-risk
populations.
Ankle brachial
pressure index
From Wikipedia, the free encyclopedia
The Ankle Brachial Pressure Index (ABPI)
is a measure of the fall in blood pressure in the arteries
supplying the legs and as such is used to detect evidence of
blockages (peripheral vascular disease see below). It is
calculated by dividing the highest
systolic
blood pressure in the arteries at the ankle and foot by the
higher of the two systolic blood pressures in the arms.
In a normal subject the pressure at the
ankle pulses is slightly higher than at the elbow (there is
reflection of the pulse pressure from the vascular bed of the
feet, whereas at the elbow the artery continues on some distance
to the wrist). The ABPI is the ratio of the highest ankle to
brachial artery pressure and an ABPI of greater than 0.9 is
considered normal.
However, a value greater than 1.3 is
considered abnormal, and suggests calcification of the walls of
the arteries and noncompressible vessels, reflecting severe
peripheral vascular disease.
Studies in 2006 suggests that an abnormal
ABPI may be an independent predictor of mortality, as it
reflects the burden of atherosclerosis.
Peripheral vascular disease (PVD) happens
when there is a narrowing of the blood vessels outside of your
heart. A substance made up of fat and cholesterol, called
plaque, builds up on the walls of the arteries that supply blood
to the arms and legs. The plaque causes the arteries to narrow
or become blocked. This can reduce or stop blood flow, usually
to the legs, causing them to hurt or feel numb. If severe
enough, blocked blood flow can cause tissue death. If this
condition is left untreated, the foot or leg may need to be
amputated.
A person with PVD also has an increased
risk of heart attack, stroke and transient ischemic attack. You
can often stop or reverse the buildup of plaque in the arteries
with dietary changes, exercise, and efforts to lower high
cholesterol levels and
high blood pressure.
Atherosclerosis (ath-er-o-skler-O-sis) is
a disease in which plaque (plak) builds up on the insides of
your arteries. Arteries are blood vessels that carry
oxygen-rich blood to your heart and other parts of your body.
Plaque is made up of fat, cholesterol,
calcium, and other substances found in the blood. Over time,
plaque hardens and narrows your arteries. The flow of
oxygen-rich blood to your organs and other parts of your body is
reduced. This can lead to serious problems, including
heart attack,
stroke, or even death.
Recently, attention has been given to indicators of
asymptomatic atherosclerosis, such as coronary artery calcium and the
ankle brachial index. ABI is the ratio of systolic pressure at the ankle
to that in the arm.
It is quick and easy to measure and has been used
for many years in vascular practice to confirm the diagnosis and assess
the severity of peripheral artery disease in the legs, the authors
write.
Gerry Fowkes, Ph.D., of the University of
Edinburgh, Scotland, and colleagues with the Ankle Brachial Index
Collaboration, conducted an analysis of data from 16 studies to
determine if the ABI provides information on the risk of cardiovascular
events and death independently of the FRS and can improve risk
prediction.
The studies included a total of 24,955 men and
23,339 women who had ABI measured at baseline and were followed up to
detect total and cardiovascular mortality.
The researchers found that the 10-year
cardiovascular mortality in men with a low ABI (0.90 or less) was 18.7
percent and with normal ABI (1.11 - 1.40) was 4.4 percent, about a four
times higher risk of cardiovascular death for men with low ABI.
Corresponding mortalities in women were 12.6
percent and 4.1 percent.
The risks remained elevated after adjusting for FRS
(2.9 for men vs. 3.0 for women). A low ABI (0.90 or less) was associated
with approximately twice the 10-year total mortality, cardiovascular
mortality, and major coronary event rate, compared with the overall rate
in each FRS category.
Inclusion of the ABI in cardiovascular risk
stratification using the FRS would result in reclassification of the
risk category and modification of treatment recommendations in
approximately 19 percent of men and 36 percent of women.
These changes [for men] from higher to lower
categories of risk would likely have an effect on decisions to commence
preventive treatment, such as lipid-lowering therapy , the authors
write.
In contrast, the main effect in women of inclusion
of the ABI would be that many at low risk with the FRS (less than 10
percent) would change to a higher risk level.
The ABI is potentially a useful tool for
prediction of cardiovascular risk. In contrast to measurement of
coronary artery calcium and carotid intima media thickness, it has the
advantage of ease of use in the primary care physicians office and in
community settings, they write.
The researchers add that the equipment is
inexpensive, the procedure is simple, and can be performed by a suitably
trained nurse or other health care professional.
The results of our study indicate that, when using
the FRS, this (considering ABI for the purposes of cardiovascular risk
assessment) may indeed be justified to improve prediction of
cardiovascular risk and provision of advice on ways to reduce that risk.
A new risk equation incorporating the ABI and relevant Framingham risk
variables could more accurately predict risk and our intention is to
develop and validate such a model in our combined data set, the authors
conclude.
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July
8, 2008 A ratio of blood pressure measurements from the ankles and
arms the ankle brachial index may improve the accuracy of predicting
cardiovascular risk, according to a review of previous research that is
reported in the July 9 issue of the Journal of the American Medical
Association.
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