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(Circulation. 2001;103:1546.)
© 2001 American Heart Association, Inc.
Clinical Investigation and Reports |
From The University of Texas Health Science Center at San Antonio (H.C.M, C.A.M), San Antonio, Tex; Southwest Foundation for Biomedical Research (H.C.M.), San Antonio, Tex; and the Louisiana State University Medical Center (A.W.Z., G.T.M., R.E.T., J.P.S.), New Orleans, La.
Correspondence to Henry C. McGill, Jr, MD, Southwest Foundation for Biomedical Research, PO Box 760549, San Antonio, TX 78245-0549. E-mail jstron{at}lsumc.edu
| Abstract |
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Methods and ResultsA
cooperative multicenter study, the Pathobiological Determinants of
Atherosclerosis in Youth (PDAY), examined the relation
of the nonlipid risk factors to atherosclerosis in 629
men and 227 women 15 to 34 years of age who died of external causes and
who had a favorable lipoprotein profile (non-HDL
cholesterol <4.14 mmol/L [<160 mg/dL] and HDL
cholesterol
0.91 mmol/L [
35 mg/dL]). In the
abdominal aorta, smokers had more extensive fatty streaks and raised
lesions than nonsmokers, and hypertensive blacks had more raised
lesions than normotensive blacks. In the right coronary artery,
hypertensive blacks had more raised lesions than normotensive blacks,
obese men (body mass index
30 kg/m2) had
more extensive fatty streaks and raised lesions than nonobese men, and
individuals with impaired glucose intolerance had more extensive fatty
streaks. Obese men had more severe lesions (American Heart Association
grade 2 through 5) of the left anterior descending coronary
artery.
ConclusionsThese substantial effects of the nonlipid risk factors on the extent and severity of coronary and aortic atherosclerosis, even in the presence of a favorable lipoprotein profile, support the need to control all cardiovascular risk factors.
Key Words: coronary disease risk factors atherosclerosis
| Introduction |
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We investigated the effects of the nonlipid risk factors on
atherosclerosis in young persons with a favorable
lipoprotein profile using data from the multicenter cooperative
project Pathobiological Determinants of
Atherosclerosis in Youth (PDAY), which collected
material from
3000 15- to 34-year-old trauma victims autopsied in
forensic laboratories. The results show that these nonlipid risk
factors deserve attention even in the presence of a favorable
lipoprotein profile.
| Methods |
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Subjects
Study subjects were persons 15 through 34 years of
age who died of external causes (accidents, homicides, or suicides)
within 72 hours of injury and were autopsied within 48 hours of death
in one of the cooperating forensic laboratories. Age and race were
obtained from the death certificate. We collected 2876 acceptable cases
from June 1, 1987, to August 31, 1994. Data on all risk factors were
available for 1479 cases. The Institutional Review Board of each
cooperating center approved this study.
Dissecting and Preserving Arteries
PDAY investigators bisected the aorta longitudinally
and fixed the left half in 10% neutral buffered formalin. They opened
the right coronary artery (RCA) longitudinally and fixed it in
the same manner. They perfused the left main artery and left anterior
descending coronary artery (LAD) with 10% buffered formalin at
a pressure of
100 mm Hg (130 cm H2O)
and dissected them from the heart. A central laboratory stained the
aortas and RCAs with Sudan IV and packaged them in plastic
bags.
In another central laboratory, a technician cut a 5-mm transverse block from the fixed LAD distal to the flow divider of the left main and left circumflex arteries. Sections from the proximal half were stained with oil red O (ORO), and sections from the distal half were stained with Gomori-trichrome aldehyde fuchsin (GTAF). Of the cases having data on all risk factors, microscopic sections of the LAD were available for 760 cases.
Grading Atherosclerosis
Three pathologists independently estimated the extent
of intimal surface area of the RCA and abdominal aorta involved with
fatty streaks and raised lesions by procedures described in previous
publications.4 The consensus
grade was the average of the grades of the 3 pathologists. Of the cases
having data on all risk factors, assessment of extent of gross lesions
was available for 1458 abdominal aortas and 1427 RCAs.
Two pathologists graded GTAF- and ORO-stained sections using the American Heart Association (AHA) classification system5 6 as described in a previous publication.7 Differences were resolved by discussion, and a consensus grade was reached.
Risk Factor Assessment
Methods of measuring CHD risk factors were
presented in previous
publications4 8 9
and are summarized in
Table 1
. We based the criterion for a favorable lipoprotein
profile on the recommendation of the National Cholesterol
Education Program3 : LDL
cholesterol <3.4 mmol/L (<130 mg/dL) and HDL
cholesterol
0.91 mmol/L (
35 mg/dL). We assumed
that an LDL cholesterol concentration of 130 mg/dL was
approximately equal to a non-HDL cholesterol concentration
of 4.14 mmol/L (160
mg/dL).10 Of the PDAY cases
with data on all risk factors, 856 cases (629 men and 227 women) had a
favorable lipoprotein profile.
|
Statistical Procedures
Extent of intimal surface area involved with
atherosclerotic lesions was analyzed by multiple regression
analysis. We included all effects found to be important in
previous
analyses.4 8 9
These were the effects of sex, race, 5-year age group, smoking status,
hypertension, obesity, and elevated glycohemoglobin, as well as the
interactions between age and the risk factors, between race and
hypertension, and between sex and obesity. Because of the limited
number of cases, effects higher than second order were not included. A
logit transformation, with a small constant added to avoid the
logarithm of zero, was applied to the extent of surface area
involved.
Because the number of cases for which we had microscopic grades was small, we combined AHA grades 0 or 1 and grades 2, 3, 4, or 5 for statistical analysis using logistic regression. We included the effects of sex, race, 5-year age group, smoking, hypertension, obesity, elevated glycohemoglobin, and the sex-by-obesity interaction.
| Results |
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Effect of Nonlipid Risk Factors on Gross
Lesions
Table 2
gives the effects of nonlipid risk factors on fatty
streaks and raised lesions in the presence of a favorable lipoprotein
profile. The effects are presented as the ratio of extent
involvement at the high level of a risk factor (as defined in
Table 1
) to the extent involvement at the desirable level
of a risk factor. Men had less extensive fatty streaks than women
(ratio <1.0) in the abdominal aorta, but men and women had about an
equal extent of raised lesions. In contrast, although men had only
slightly more extensive fatty streaks in the RCA than women (ratios
slightly >1.0, P=NS), they
developed considerably more extensive raised lesions in both the 15- to
24-year-old and 25- to 34-year-old age groups.
|
Smoking was associated with more extensive fatty streaks in the abdominal aorta in both the 15- to 24-year-old and 25- to 34-year-old age groups and with a much greater extent of raised lesions in the abdominal aorta of 25- to 34-year-old subjects. It had little effect on the extent of either type of lesion in the RCA.
Hypertension was associated with a greater extent of raised lesions in the abdominal aorta and RCA of blacks. Hypertension tended to be associated with more extensive raised lesions in whites, but the effect was smaller than in blacks of the same age. We believe that the ratio of 0.55 for raised lesions in the abdominal aorta of younger whites is due to the low prevalence of hypertension in the younger age group and does not represent a real effect of hypertension. Hypertension was not associated with fatty streaks in either whites or blacks.
Obesity was associated with more extensive fatty streaks in the RCAs of 15- to 24-year-old men and with more extensive raised lesions in both 15- to 24-year-old and 25- to 34-year-old men. Obesity was not associated with either fatty streaks or raised lesions in the RCAs or aortas of women.
Elevated glycohemoglobin was associated with more extensive fatty streaks in the RCAs of 15- to 24-year-old men and women, but the associations with raised lesions were not significant, probably because of the low prevalence of elevated glycohemoglobin.
Effects of Nonlipid Risk Factors on Microscopic
Characteristics of Lesions
Eighteen (4.2%) of 430 cases had AHA grade 4 to 5
(advanced) lesions in the LAD. One of the women with a grade 4 to 5
lesion had no risk factors, and 3 had 1 risk factor. Three of the men
with a grade 4 to 5 lesion had no risk factors, 5 had 1 risk factor,
and 6 had 2 risk factors.
Table 3
shows the odds ratios for AHA grades 2 to 5 (fatty
streaks and advanced lesions) versus AHA grades 0 to 1 (normal and
isolated foam cells). All of the odds ratios (except that for smoking)
were substantially >1.0, and the odds ratios for male sex and obesity
in men were statistically significant. The lack of statistical
significance is probably due to the limited number of
cases.
|
Effect of Combined Risk Factors
The
Figure
compares the extent of raised lesions in the RCAs of persons who did
not smoke, were normotensive, were not obese, and had normal
glycohemoglobin with the extent of raised lesions in persons who
smoked, were hypertensive, were obese, and had elevated
glycohemoglobin. All had a favorable lipoprotein profile. The
differences were substantial, even in the 15- to 19-year-old age group
and in both men and women. Differences became greater in succeeding age
groups and were 5-fold higher in men aged 30 to 34 years. These risk
factor profiles illustrate the extreme profiles of no risk factors and
all risk factors. The extent of raised lesions for other profiles will
be intermediate.
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| Discussion |
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Male Sex
Although male sex is not among the mutable risk
factors, the results presented here emphasize the more rapid
progression of coronary atherosclerosis in
young men than in young women. This difference is not explained by
established risk factors. The difference between young men and young
women in atherosclerotic lesions precedes the difference between the
sexes in clinical CHD at older ages. This observation is
consistent with the concept that risk factor reduction in young
people will prevent or delay the development of clinical
CHD.
Smoking
The strongest effect of smoking is on a localized
region of the dorsolateral aspect of the distal third of the abdominal
aorta.11 The effect is
evident in the late teenage years and becomes stronger in later
decades. This finding is consistent with the well-established
association of smoking with abdominal aortic
aneurysm.12 Smoking
is associated with a higher microscopic grade of coronary
artery fatty streaks in young
people,7 but a stronger
effect on raised lesions becomes evident after age
35.13 Smoking is associated
with increased risk of clinical CHD in the presence of low serum
cholesterol
levels,14 a finding
consistent with the results reported
here.
Hypertension
In the PDAY study, hypertension was the only risk
factor that affected raised lesions but not fatty
streaks.9 This effect
remained strong in the presence of a favorable lipoprotein profile. As
in previous analyses of these cases, the effect was stronger in
blacks, probably due to the greater severity of hypertension in
blacks.
Obesity
Obesity is the only risk factor in the PDAY study that
affects atherosclerotic lesions in men but not in
women.8 Its effect is not
explained by other risk factors. The present results show that
obesity does not depend on the presence of an unfavorable lipoprotein
profile to accelerate atherogenesis.
Impaired Glucose Tolerance
In a previous analysis of PDAY
cases,8 elevated
glycohemoglobin was associated with a significant 3-fold excess of
raised lesions in the RCAs of persons 15 to 24 years of age and a
5-fold excess in persons 25 to 34 years of age, even when adjusted for
other risk factors. In this smaller number of cases with a favorable
lipoprotein profile, the effect was significant only for RCA fatty
streaks. The ratios
(Table 2
) for raised lesions were greater than 1.0 but not
significantly greater, probably because the number of cases having
elevated glycohemoglobin was too small.
Limitations of Study
Because emergency medical teams often administer large
quantities of intravenous fluids to some individuals
immediately before death from violent causes, we excluded serum values
from cases having total cholesterol <2.59 mmol/L (100
mg/dL).4 The selection of
desirable lipoprotein profiles having non-HDL cholesterol
and HDL cholesterol concentrations at opposite ends of the
distributions also minimizes the potential effects of hemodilution.
Although agonal procedures may degrade associations, we do not believe
that they are likely to produce spurious
associations.
Comparison With Other Studies
The effects of the nonlipid risk factors reported here
are consistent with the risk factor effects estimated from all
PDAY
cases.4 7 8 9 11
Those analyses did not indicate interactions between the lipid
and nonlipid risk factors. Because those analyses used a larger
number of cases, some risk factor effects were statistically
significant, whereas effects of similar magnitude were not
statistically significant in the smaller number of cases
analyzed for the present report.
The Bogalusa Heart
Study15 examined the effects
of multiple risk factors on atherosclerosis in 93 young
persons between 2 and 39 years of age (average
20 years). The
severity of atherosclerosis increased as the number of
risk factors increased, but the authors did not analyze the
effects of nonlipid risk factors in the presence of a favorable
lipoprotein profile.
Prevalence of Nonlipid Risk Factors
Table 1
shows a high prevalence of nonlipid risk factors
among these young people having a favorable lipoprotein profile. The
high prevalence of smoking in PDAY cases (44%) is consistent
with recent reports of prevalence of smoking among high school
students16 and young
adults,17 with the
prevalence being highest (28.7%) among persons 18 to 24 years old.
PDAY cases showed an even higher prevalence because we used an
objective marker of
smoking18 and because there
is an association of smoking with high-risk behaviors that predispose
those who smoke to traumatic
death.19
The prevalence of hypertension among young white and black
men and women observed in PDAY is consistent with prevalence of
hypertension observed in a living
population.20 Although only
4% of PDAY cases had glycohemoglobin
8%, indicating an average
blood glucose >140 mg/dL during several weeks preceding death, this
figure may underrepresent the true prevalence of insulin
resistance and impaired glucose tolerance. Type II diabetes, elevated
fasting glucose, and impaired glucose tolerance are increasing in
prevalence,21 together with
obesity, particularly in younger men and
women.22
Implications for Prevention of CHD
The high prevalence of nonlipid risk factors indicates
considerable potential to affect early atherosclerosis
and subsequent CHD by modifying these risk factors even among those
young people with a favorable lipoprotein profile. Changing the
behavior of young people to reduce cardiovascular risk
is a serious challenge and a difficult task. Efforts to modify diet in
children by intervention in school lunch programs and by family
counseling have achieved only limited
success.23 24 The
decline in adolescent and youth smoking since 1974 slowed after 1985
and now is reversed.25
Obesity is emerging as a major health
problem.26
Despite the controversy over screening for blood cholesterol, diet modification, and drug treatment at early ages, there is little or no controversy over hygienic measures to control smoking, obesity, hypertension, and hyperglycemia in young persons. As demonstrated in the results presented here, these nonlipid risk factors substantially affect the extent and severity of coronary and aortic atherosclerosis even in individuals with a favorable lipoprotein profile. The earlier all the cardiovascular risk factors are controlled, as recommended by the AHA in 1992,27 the greater the potential for deferring the onset of CHD.
| Acknowledgments |
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| Footnotes |
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Received September 27, 2000; revision received November 21, 2000; accepted December 1, 2000.
| References |
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