Download The Relationship between body mass index and severity of coronary

Introduction:
Prevalence of obesity is increasing all over the world; this increase is noticeable even
in countries in which there has not previously been an overweight and obesity
problems. 1
Overweight and obesity are associated with increased morbidity and mortality. For
example, in the United States, for the first time since the Civil War, there are
estimates for a decrease in life expectancy due to diseases and disorders related to
obesity; including high blood pressure, dyslipidemia, and some types of cancer.2
Body mass index, weight in kilograms divided by the square of height in meters, is
frequently used as a surrogate for assessment of obesity. 3
The association between obesity and classic cardiovascular disease risk factors, such
as, diabetes mellitus, hypertension, dyslipidemia and metabolic syndrome, is known
for very long time. Moreover, large longitudinal studies in subjects without known
CVD have documented an independent positive association of general and central
obesity with cardiovascular events.4-6
On the other hand, a contradictory protective effect of obesity as assessed by
increased BMI, known as ‘‘obesity paradox,’’ has been previously reported in various
groups of cardiovascular patients; an improved prognosis in obese compared to lean
subjects has been shown in patients with known or suspected coronary artery disease
(CAD) 7-10, heart failure 11, 12, or following coronary angioplasty.4, 13
The association between BMI and angiographic coronary atherosclerosis in patients
undergoing coronary angiography has been little studied. The aim of the present study
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was to determine the association between obesity assessed with BMI and severity of
CAD assessed with invasive coronary angiography (ICA) in our locality
Methods:
This is a prospective study, enrolled 415 consecutive subjects who underwent
Invasive Coronary Angiography (ICA) for different indications. (Figure 1)
Figure 1: Indications for invasive coronary angiography in the study group.
The study was conducted in a single institution (Department of Cardiology,
University Hospital of ASSIUT, EGYPT) during a 6 months period, from March to
September 2013.Approval for the study obtained from local ethical committee.
Written informed consent was obtained from all patients.
Patients with suspected or documented congenital heart disease, hypertrophic
obstructive cardiomyopathy, as well as those on hemodialysis, were excluded from
the study.
In all subjects, a full medical history was taken, and a complete physical examination
was performed. Cardiovascular risk factors were recorded in detail, and all patients
underwent invasive coronary angiography.
The study protocol was approved by the local Ethics Committee. The study complied
with the Declaration of Helsinki, and all participants provided written informed
consent.
The cardiovascular risk factors assessed in the present study were age, gender, family
history of CAD, smoking habits, hypertension, hypercholesterolemia, and diabetes
mellitus. A positive family history of CAD was determined by the presence of a first
degree relative with a cardiovascular event at an age <65 years for women and <55
years for men. Smokers were defined as those who were smoking at the time of
enrollment or had stopped for <12 months. Hypertension was defined as systolic
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blood pressure (SBP) >140 mmHg and/or diastolic blood pressure (DBP) >90 mmHg
during the initial evaluation or administration of anti-hypertensive medications.
Hypercholesterolemia was defined as low-density lipoprotein cholesterol (LDL-c)
>160 mg/dl or total cholesterol >240 mg/dl or administration of anti-cholesterolemic
medications (statins or fibrates). Diabetes was defined as a fasting blood glucose
concentration ≥126 mg/dl or administration of anti-hyperglycemic medications.
BMI was calculated as weight in kg divided by the square of height in meters. Obesity
was classified according to the BMI using the National Institute of Health (NIH)
criteria as: Lean (BMI 18–24.9 kg/m2), overweight (BMI 25–29.9 kg/m2), obese
(BMI ≥ 30 kg/m2).14
Coronary angiography was performed according to the standard Judkins techniques
through femoral or radial approach (Integris 3000, Philips Medical Systems,
Netherlands). Images were acquired in optimal projection angles, at 25 frames per
second, and were digitally recorded on Xcelera workstation.
Two experienced operators visually assessed all coronary angiograms, and a
consensus was reached. Significant CAD was defined as ≥ 50% stenosis in the
internal diameter of at least one coronary artery ≥ 2 mm in diameter. To describe the
extent of CAD, patients with CAD were distinguished in those with single-vessel
versus multivessel disease (MVD): which defined as the presence of significant CAD
in ≥ two epicardial coronary arteries. Left main affection was classified into a separate
category.
Statistical Analysis
Continuous variables are expressed as mean and standard deviation, and categorical
variables are presented as frequencies and percentages. Patients were divided into
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three groups according to BMI class. Baseline patient's characteristics were compared
using analysis of variance (ANOVA) for continuous variables, a chi-square (X2) test
for dichotomous variables, and fisher exact test for dichotomous variables with fewer
than 5 patients in the category. Univariate analysis was performed using X2 test with
Yates’ correction when necessary. Multivariate logistic and linear regression analyses
were performed using all potentially relevant variables to identify baseline
independent predictors of CAD intensity. All p-values were two-tailed, and statistical
significance was defined if p <0.05. All analyses were performed with SPSS version
16.0 statistical software (SPSS Inc., Chicago, IL, USA).
Results:
This cohort comprised of 415 consecutive subjects. Baseline characteristic patients
are shown in Table 1. The mean BMI of the study group was 31.2 ± 4.8 kg / m2. Lean
patients were 89 (21.5%) with mean BMI of 23.6±1.2 kg / m2 (range 20.2-24.9), over
weight patients were 121 (29.1%) with mean BMI of 27.6±1.4 kg / m2 (range 25.129.9) meanwhile, obese patients were 205 (49.2%) with mean BMI of 32.8±2.3 kg /
m2 (range 30.1-40.4).
Obese patients were associated with higher prevalence of hypertension, diabetes and
hypercholesterolemia (Table 1). A non significant trend toward younger age in obese
patients at time of ICA, and a higher prevalence of smoking was present. There was
no significant difference in the overall incidence of significant CAD between the three
groups where almost 90% of lean, obese and overweight patients had CAD (Table 1).
Results of ICA in different BMI classes are presented in Table 2. There's no
significant difference in the angiographic procedure, radiation exposure, fluoroscopy
time, contrast amount and coronary anatomy between the three groups. The
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prevalence of single, two or three vessel disease did not differ significantly between
the 3 BMI classes. Furthermore, the prevalence of LM disease was comparable
between different groups as shown in Table 2. Multivariate regression showed that
advanced age (OR=1.1, 95 % CI =1.02-6.1), hypertension (OR=2.46, 95 % CI= 1.155.90), diabetes mellitus (OR= 3.1,95 % CI = 1.9-5.7) and dyslipidemia (OR=1.2, 95
% CI = 1.01-6.86) were independent predictors of MVD. On the other hand, obesity
(OR=1.23, 95 % CI=0.65- 2.2), and overweight (OR=1.12, 95 % CI=0.65- 2.2) did
not predict presence of MVD in our study population (Table 3). Left main affection,
also did not had significant relationship with neither over weight (OR= 0.84, 95 %
CI=0.25-2.2), nor obesity (OR=1.01, 95 % CI =0.34-3.65) (Table 3).
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Discussion:
The findings of this study indicated that increased BMI class was not related to a
higher incidence of significant angiographic CAD in patients underwent ICA.
Although obese patients had higher prevalence of hypertension, diabetes and
hypercholesterolemia, higher BMI class failed to predict the prevalence of three
vessels or left main affection, after adjusting for other major CAD risk factors.
Obesity and overweight has traditionally been considered a cardiovascular risk factor
and has been associated with an increased risk of developing CAD and mortality in
the general population.
Thus, it may be speculated that obese patients should have worse outcomes than their
non obese counterparts 5, 6, 15. Nevertheless, among patients with known CAD 7-10,
heart failure 11, 12or multiple risk factors 16, and post coronary angioplasty 4, 13, a
paradoxically improved prognosis has been described in obese compared to lean
patients (obesity paradox).
In accordance with our results, Hodgson et al18, and Rossi el al19 reported that there
was no significant association between BMI and the presence or extent of
angiographic CAD in patients at risk for CAD. On the other hand, Rubinshtein et al.17
Found that obesity was not only non predictor, but also, it was associated with less
severe coronary artery disease among patients undergoing coronary angiography.
Obese patients were found to have a low prevalence of high-risk coronary anatomy
(HRCA) compared to non obese comparators. They attributed their results to early
referral of obese persons for coronary angiography. This could not apply on current
study because most of patients had acute coronary syndrome. However, in the current
study, obese and overweight patients tend to be younger than lean patients.
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Several studies have reported inconsistent results regarding the association of BMI
with the occurrence and severity of angiographic CAD. In patients referred for
angiography with suspected CAD or acute coronary syndromes, BMI was inversely
associated with the presence and severity of CAD 17-19; in one study, this association
was lost after adjustment for risk factors 16.
The potential mechanisms underlying the ‘‘obesity paradox’’ have been little studied.
It has been suggested that these findings was explained by the lack of discriminatory
power of BMI to differentiate between body fat and lean mass20. In contrast to BMI,
central obesity measured by waist circumference has been proposed to be more
appropriate for the assessment of the obesity-related cardiovascular risk in patients
with 9, 21 or without 5, 9, 21, 22 known CVD. Another explanation of those negative
results is the lack of physical fitness assessment. Low cardiorespiratory fitness is a
strong predictor of CVD and all-cause mortality in men and women23, 24.
Cardiorespiratory fitness alters obesity dynamics such that obese men survive better
only if they register high fitness. Similarly, it explains why some obese individuals
are not at risk and why a substantial reduction in mortality risk is even observed in
obese adults with moderate fitness compared with those with low fitness 23, 24.
Quantitative assessment of physical activity is difficult, most of studies that tested the
relationship between CAD and obesity did not examine physical activity of their
patients.
5. Study Limitations:
This was a prospective cohort observational study single center with relatively small
number of patients. Assessment of waist circumference and physical activity is an
important confounder which affects morbidity and mortality in obese persons. Larger
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registries with assessment of these confounders are needed to confirm or counteract
our results especially in our locality.
6. Conclusion:
Obesity and overweight, measured by BMI, were not related to the severity of CAD in
patients underwent ICA.
Conflict of interest:
Nothing to declare
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