Obesity and coronary intervention: should we continue to use Body Mass Index as a risk factor?

Tarastchuk, José Carlos Estival; Guérios, Ênio Eduardo; Bueno, Ronaldo da Rocha Loures; Andrade, Paulo Maurício Piá de; Nercolini, Deborah Christina; Ferraz, João Gustavo Gongora; Doubrawa, Eduardo

doi:10.1590/S0066-782X2008000500001

Abstracts

BACKGROUND: Central anthropometric indexes are better than the body mass index to discriminate elevated coronary risk. However, the Body Mass Index (BMI) is still the most frequently studied anthropometric index on outcomes of patients undergoing percutaneous coronary angioplasty (PCI). OBJECTIVE: To recognize, among several anthropometric indexes of obesity, which one best discriminates MACE (Major Adverse Cardiac Events) after PCI. METHODS: Subjects were 308 patients (mean age 61.92±11.06 years, 60.7% of them men) who had undergone successful coronary angioplasties. Six months after the procedure, patients were contacted for clinical follow-up. Major Adverse Cardiac Events included death, acute myocardial infarction, cardiac surgery, reintervention, angina, or evidence of myocardial ischemia on a non-invasive test. Patients were divided into 2 groups: Group 1 (with MACE, n=91, 29.5%), Group 2 (with no MACE, n= 217; 70.45%). For men and women, the anthropometric indexes studied and their respective cut-off points were waist circumference >90/80 cm, Waist-Hip Ratio > 0.90/0.80cm, Conicity Index > 1.25/1.18, and Body Mass Index > 30. RESULTS: There were more cases of familial history and previous infarct in Group 2. For men, waist circumference >90cm (p=0.0498) in multivariate analyses was an independent predictor of MACE. BMI was not related to MACE. In Group 1, the prevalence of an elevated BMI was significantly different compared to the other anthropometric indexes studied (p<0.0001). CONCLUSION: Waist circumference was an independent predictor of MACE in men. Body Mass Index was not related to MACE and was the least frequent anthropometric index in the MACE group.

Obesity; antropometry; body mass index; angioplasty, transluminal, percutaneous coronary

FUNDAMENTO: Para discriminar risco coronariano elevado, indicadores de obesidade central são melhores do que o Índice de Massa Corpórea (IMC), que é ainda o índice antropométrico (IA) mais utilizado para seguimento após intervenção coronariana percutânea (ICP). OBJETIVO: Reconhecer, entre os índices antropométricos (IA), os que melhor se correlacionam com ocorrência de desfechos após intervenção coronariana percutânea (ICP). MÉTODOS: Foram considerados 308 pacientes (p), idade média de 61,92±11,06 anos, 60,7% do sexo masculino, submetidos a ICP com stent. Após seis meses, pesquisaram-se os desfechos: óbito, reintervenção por ICP ou cirurgia cardíaca, exame não-invasivo alterado por isquemia ou sintomas anginosos. Os p foram divididos em: Grupo 1 (com desfechos, n=91; 29,5%) e Grupo 2 (sem desfechos, n=217; 70,45%). No sexo masculino e feminino, os IA estudados e seus respectivos pontos de corte foram: circunferência abdominal (CA) > 90/80 cm, relação cintura-quadril (RCQ) > 0,90/0,80cm, índice de conicidade (IC) >1,25/1,18 e índice de massa corpórea (IMC) >30 para ambos os sexos. RESULTADOS: Os grupos diferiram quanto à maior ocorrência de histórico familiar e infarto prévio no Grupo 2. No sexo masculino, CA > 90 cm (p=0,0498) foi, em análise multivariada, preditor independente de desfechos. IMC não foi preditor de eventos. No Grupo 1, a probabilidade de ocorrência de IMC alterada é significativamente menor do que a ocorrência dos outros IA estudados (p<0,0001). CONCLUSÃO: CA anormal comportou-se como preditor independente de ocorrência de desfechos no sexo masculino dessa população pós-ICP. IMC elevado não foi preditor de desfechos e foi o índice antropométrico menos prevalente em pacientes com eventos.

Obesidade; antropometria; índice de massa corporal; angioplastia transluminal percutânea coronária

ORIGINAL ARTICLE

Hospital Universitário Evangélico de Curitiba, Curitiba, PR - Brazil

Mailing address

SUMMARY

BACKGROUND: Central anthropometric indexes are better than the body mass index to discriminate elevated coronary risk. However, the Body Mass Index (BMI) is still the most frequently studied anthropometric index on outcomes of patients undergoing percutaneous coronary angioplasty (PCI).

OBJECTIVE: To recognize, among several anthropometric indexes of obesity, which one best discriminates MACE (Major Adverse Cardiac Events) after PCI.

METHODS: Subjects were 308 patients (mean age 61.92±11.06 years, 60.7% of them men) who had undergone successful coronary angioplasties. Six months after the procedure, patients were contacted for clinical follow-up. Major Adverse Cardiac Events included death, acute myocardial infarction, cardiac surgery, reintervention, angina, or evidence of myocardial ischemia on a non-invasive test. Patients were divided into 2 groups: Group 1 (with MACE, n=91, 29.5%), Group 2 (with no MACE, n= 217; 70.45%). For men and women, the anthropometric indexes studied and their respective cut-off points were waist circumference >90/80 cm, Waist-Hip Ratio > 0.90/0.80cm, Conicity Index > 1.25/1.18, and Body Mass Index > 30.

RESULTS: There were more cases of familial history and previous infarct in Group 2. For men, waist circumference >90cm (p=0.0498) in multivariate analyses was an independent predictor of MACE. BMI was not related to MACE. In Group 1, the prevalence of an elevated BMI was significantly different compared to the other anthropometric indexes studied (p<0.0001).

CONCLUSION: Waist circumference was an independent predictor of MACE in men. Body Mass Index was not related to MACE and was the least frequent anthropometric index in the MACE group.

Key words: Obesity; antropometry/methods; body mass index; angioplasty, transluminal, percutaneous coronary.

Introduction

Since 1983 when the results of the Framingham Study related to obesity were published, a strong correlation between this risk factor and coronary artery disease has been observed¹. In Brazil, the prevalence of obesity is approximately 8% for men and 12.4% for women². The joint effect of overweight and obesity reaches figures of around 38.5% and 39% for men and women, respectively. In the United States, this rate is approximately 30.5% and 64.5%, for men and women, respectively i.e., more than half of the North American population is overweight or obese³.

Using the BMI as a marker for obesity, significant epidemiological studies have shown that obesity is associated with cardiovascular morbidity and mortality^1,4. The association of obesity with conventional risk factors, such as arterial hypertension and diabetes mellitus, and with endothelial dysfunction, insulin resistance, and inflammation may contribute to the increase in untoward outcomes after Percutaneous Coronary Interventions (PCI) in obese individuals⁵.

Despite evidence of risk conferred by an elevated BMI, there are reports in literature of a paradoxal protection afforded by obesity in patients submitted to PCI^6-9. Thus, in these publications, patients with high BMIs showed lower rates of cardiac events in one year^6,7, lower risks of intrahospital events⁸, and lower mortality rates after the procedure⁹.

Although the BMI is a simple and convenient measurement considered valid up until now for the study of obesity, measurements of central obesity (primarily Waist Circumference and altered Waist-Hip Ratios)¹⁰ have proved to be more closely related both to elevated coronary risks^11,12 and to acute myocardial infarcts^13,14. Even so, to date, BMI is the anthropometric index most used in interventional cardiology for clinical follow-up after a coronary intervention.

The objective of this study is to recognize, among several anthropometric indices of obesity, those that best correlate with the occurrence of post-PCI outcomes.

Methods

The sample is composed of 308 consecutive patients, mean age 61.92±11.06 years (varying from 34 to 88 years), 60.7% of them male, successfully submitted to PCI with a conventional stent during the period from May 2005 to September 2006. For all study subjects, a routine medical history was taken with the collection of information on risk factors for coronary disease. Patients were submitted to physical examinations, with weight and height measurements. The BMI was calculated by the weight in kilograms divided by the height in square meters (kg/m²). Obesity was considered when BMI > 30. The Waist/Abdominal Circumference (WC), obtained with the patient wearing the least amount of clothing possible, was measured at mid-distance between the last floating rib and the iliac crest. Hips were measured using as reference the femoral trochanters. The Waist-Hip Ratio (WHR) was determined by dividing the Waist Circumference by the Hip Circumference (HC). The Conicity Index (CI) was determined using measurements of body weight, height, and wais circumference, with the following equation:

CPIs were carried out via femoral artery using a technique chosen by current consensus¹⁵. Patients were pretreated with double platelet inhibition, receiving aspirin 100mg and ticlopidine 250mg, twice a day, initiated 48 hours before, or clopidogrel 75mg (initiated at least 24 hours before the procedure, once a day, or with a loading dose of 300mg 6 hours before the procedure), and this approach was maintained for 30 days after the intervention. No patient received glycoprotein IIb/IIIa inhibitors. Success in the procedure was defined as the achievement of residual stenosis < 30%, with no occurrence of a significant clinical event (death, acute myocardial infarct (AMI), or need for emergency surgery), during the hospital phase.

After a 6-month period, patients were contacted in search of the following outcomes: death, reintervention with PCI or vessel-related heart surgery, non-invasive test altered by ischemia, acute myocardial infarct, or recurrence of anginous symptoms^16,17. Outcomes were considered the most serious events reported. The occurrence of unfavorable outcomes was correlated with the anthropometric indices obtained. In men and women, the anthropometric indices studied and their respective cut-off points for both genders were Waist Circumference > 90/80cm, Waist-Hip Ratio >0.90/0.80cm¹⁸, Conicity Index >1.25/1.18¹¹, and Body Mass Index (BMI) >30¹⁹.

As to statistical analyses, the groups were compared with the use of dichotomic variables, Fisher's Exact Test, and, for continuous variables, Student's t Test (independent samples), except for the "initial lesion and residual lesion" variables which were analyzed with the Mann-Whitney non-parametric test. To study dichotomized anthropometric variables, Fisher's Exact Test and Wald's Test were used. In order to verify the prevalence of abnormality of each anthropometric index studied, the Binomial Test was used. All anthropometric variables studied were submitted to univariate and multivariate analyses. P values less than 5% (p<0.05) were considered significant.

Results

Three hundred and eight patients who successfully received metallic stent implants between May 2005 and September 2006 were studied. According to the outcomes, they were divided into Group 1 (with outcomes, n=91; 29.5%) and Group 2 (no outcomes, n=217; 70.45%). Graphic 1 demonstrates the proportion of outcomes found in patients who experienced events. Characteristics of the population studied are listed on Table 1.

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A statistically significant difference was observed between the groups for the items familial history of coronary disease and prior infarct, more prevalent in Group 2 (p=0.02 and 0.03, respectively). The other clinical and angiographic characteristics were similar between the groups. The rates of immediate success, mean final stenosis, and complications were similar between the two groups.

No independent influence was shown of the variables studied on the occurrence of events in the univariate and multivariate statistical analyses (the latter included all altered anthropometric parameters available, except the Waist-Hip Ratio) of the occurrence of altered anthropometric indices and outcomes in the general population and in women. In men, on the other hand, the Waist Circumference >90cm in the multivariate analysis (p=0.0498) was independently related to the occurrence of outcomes. The BMI was not a predictor of events in either gender (Tables 2, 3 e 4).

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Despite the fact that most of the patients in the sample had abnormal anthropometric indices, we noted the order of occurrence of each altered anthropometric measurement in the group with outcomes. In this way, in Group 1, the probability of the occurrence of abnormal Waist Circumferences (61.36%), Waist-Hip Ratios (94.48%), and Conicity Indices (64.29%) is significantly different from the probability of BMI abnormalities (26.30%), with p<0.0001 for all combinations (Table 5).

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Discussion

In this study of patients submitted to PCI with a conventional stent, it was noted that the altered waist circumference stands out as an independent predictor for the occurrence of late outcomes in the male sub-group. The BMI was not associated with a better or worse clinical progress after PCI.

Various studies published have shown the existence of a protective effect of obesity (according to the BMI) in patients submitted to PCI. Gruberg et al⁶ reported a lower number of cardiac events in obese individuals, a protection that remained for up to one year after the PCI. Ellis et al²⁰, before the advent of stents, observed poorer intrahospital clinical developments only in patients with extreme BMIs (equal to or lower than 25 and greater than 35), and this finding is a predictor of death after PCI²⁰. There are reports of greater risks of vascular complications in patients with extreme BMIs when compared to moderate obesity, which supports the existence of a paradox of obesity²¹. In studying patients submitted to the primary PCI in the Cadillac study, Nikolski et al⁹ observed a correlation between elevated BMIs and lower mortality⁹. In evaluating the relationship between the BMI and one-year clinical progress after PCI, Kelly et al⁷ observed that the BMI was associated with greater efficacy and less bleeding after PCI. In this sample, there was an extra advantage for patients with high BMIs randomized to receive clopidogrel⁷. The so-called "obesity paradox" has also been observed in patients after heart surgery²² and in those with congestive heart failure²³. The BARI study reported a better short-term clinical progress in obese individuals in the PCI arm, and the BMI showed no association with the 5-year mortality rate⁸. Presently, there is no plausible explanation for the paradoxal protection of obesity. A greater coronary diameter in the obese, with a smaller chance for restenosis⁸, and the influence of age, which may be lower in the obese patients studied, may have influenced the superior clinical course²⁴; even excessive anticoagulation in patients with higher BMIs⁶ is a possible mechanism to justify these findings in medical literature. More recently, Rubinstein et al²⁵ studied the severity of coronary artery disease in obese subjects submitted to PCI and concluded that the obese showed a smaller prevalence of serious coronary lesions, which might also explain the better clinical progress in this group of patients.

There is controversy, however, regarding this issue. Some studies have not shown the protective effect of obesity after coronary intervention: data from the TAXUS-IV study, with angiographic control post-PCI with metallic stent implantation, showed a worse clinical progress in the obese when compared to patients with normal BMIs²⁶. A sub-analysis of the ARTS study²⁷, in observing outcomes three years after PCI or cardiac surgery, failed to show any association between the BMI and significant cardiac events. Rana et al²⁴ did not note any relationship between the metabolic syndrome or any of its components (among them, an elevated BMI) and a smaller occurrence of post-PCI outcomes. Poston et al²⁸, in evaluating the impact of obesity after PCI (quality of life or health status after 12 months in one large cohort of patients with 1631 individuals), perceived that there was no long-term difference in health status, quality of life, need for repeated procedures, or survival in the different classifications of BMI²⁸. This author, when studying 903 patients after angioplasty with conventional stents, found no protection afforded by obesity against outcomes 6 months after the procedure. In the normal BMI, overweight, and obese groups, the occurrence of untoward events did not differ significantly²⁹.

Although anthropometric indices of central obesity bear a better correlation with coronary events¹⁴, high coronary risk¹¹, and AMI¹³, there are no studies correlating them with the clinical progress after PCI. In fact, despite the fact that BMI is a simple and convenient measurement for the diagnosis of obesity, the importance of the deleterious effect of abdominal obesity on coronary artery disease is increasingly more evident¹⁰. Compared to the BMI, the Waist Circumference, Conicity Index, and Waist-Hip Ratio have proved to be superior for identifying visceral adiposity and, consequently, metabolic disorders and cardiovascular risk¹². In a study on risk factors in the city of São Paulo and in INTERHEART, a high Waist-Hip Ratio (intermediate tercile versus the inferior tercile) was independently associated with AMI, which did not occur with an altered BMI^13,14.

All these recent findings on the importance of central obesity (Waist Circumference, Waist-Hip Ratio, and Conicity Index) in detriment of generalized obesity measurements (BMI), added to the results of this study, lead us to question the true existence of the paradox of obesity, a finding based merely on the calculation of the BMI. Additional research - especially with a greater number of individuals allocated - on the influence of anthropometric indices on the interventional cardiology scene should be carried out for definitive conclusions on the theme.

Limitations of the study - Since it is a populational sample of the real world comprised by consecutive patients submitted to PCI, most of the women presented central obesity, which could explain the statistical non-significance in this group. Since there was a high percentage of abnormality (94.48%) in the Waist-Hip Ratio in the general population, with an absence of cases in the group of women with Waist-Hip Ratios < 0.80, this anthropometric measurement was not included in the Logistic Regression model. The sample size and level of significance should be taken into consideration in interpreting the results, and the reader should await larger studies in order to confirm the hypotheses presented.

Conclusion

Abnormal Waist Circumference, an anthropometric index that reflects central obesity, behaved as an independent predictor of the occurrence of outcomes in the male individuals of this population post-PCI. An elevated BMI was not a predictor of outcomes in either gender, and was the least prevalent anthropometric index in patients with outcomes, despite being the most frequently used in worldwide literature.

Potential Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Sources of Funding

There were no external funding sources for this study.

Study Association

This study is not associated with any graduation program.

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