In underweight, normal weight, overweight and obese patients, the mortality rate after one year discharge was 3.3%, 1.8%, 1.8% and 0 respectively, with no significant difference between the groups (P = 0.508). When combining underweight with normal weight, or overweight with obese patients, the outcomes difference between the new generated three groups was still not significant (P > 0.05).
Our study was one of the limited studies in evaluating the association between BMI and clinical outcomes in elderly patients. Mehta et al. showed that the mortality rate of the obese patient was significantly lower than normal weight or underweight patient at hospital, and at 6 or 12 month follow-up. However, in the multivariate analysis, only older age (not the increased BMI value) was the strongest predictor of mortality at 1 year. Elderly patients are more likely to have normal weight or underweight while younger patients are more likely to find “fatter.” Adverse cardiovascular events occurred more in older patients than in younger ones regardless of the treatment. So the better outcomes in patients with high value of BMIs might attribute to the benefit of their young age. We also observed that the medication prescriptions varied in patients with different BMIs. Diercks et al. reported that obese patients with acute coronary syndrome were more likely to receive aggressive medication than normal weight and underweight patients, and adverse cardiovascular events also occurred less in those patients. Steinberg et al. reported a lineal association between increased use of guideline-based medications and increased value of BMIs in 130,139 CAD patients. So the “obese paradox” could be mistakenly interpreted by confounders, such as age or medications.
In the present study, normal weight (45.4%) and overweight (41.5%) patients accounted the majority parts of all the patients. Obese and underweight patients only accounted about 10% of all the patients. This composition in the elderly patients in China is different from the younger patients and western patients. In the United States or Europe, approximately 70% of the patients are overweight or obese, whereas only 30% of the patients had normal or lower BMIs. A number of risk factors did not increase as BMI raised. Nikolsky et al. recently evaluated the association between BMI and clinical outcomes in patients undergoing primary PCI, and found the better outcomes in obese patients attributed to their better renal function. The present study showed that the rates of renal dysfunction (glomerular filtration rate <60 ml/min) in underweight, normal weight, overweight, and obese patients were 86.7%, 68.3%, 43.8% and 30.9%, respectively, which confirmed previous findings. Meanwhile, a higher rate of anemia in patients with a lower value of BMI was also observed in the elderly patients. So the obesity paradox indicating the protective status of BMI may not be precise as it could also be confounded by patients’ comorbidities.
Since the association between BMI and the new developed cardiovascular events are not agreed in different studies. Researchers assumed that BMI may not be an appropriate predictor for MACE. The deficiency of BMI is the inability of it in discriminating between an excess weight in body fat and in lean mass. Increased weight as body fat was harmful but increased lean mass was associated with better fitness and exercise capacity. Thus, BMI may not be a reasonable surrogate to represent adiposity. Romero-Corral et al. showed that when BMI >25 kg/m2, it showed poor specificity to detect excess body fat. On the contrary, waist circumference and waist-hip-ratio were more representative of lipid level, also sensitive and accurate in predicting short-and long-term cardiovascular events. Underweight patients are usually at higher risk of heart failure and mortality, and we assumed it attributed to the low value of lean mass, which still needed to be confirmed.
Several limitations have to be taken into consideration. First, this study only used BMI as surrogate for the lipid level, while waist circumference and waist-hip-ratio have shown to be more accurate in predicting MACE. However, due to the retrospective design, the capacity of those surrogates could not be compared. Second, the outcomes of extremely obese patients (BMI > 35 kg/m2) were not separately analyzed due to the limited number of the patients. As data from the National Cardiovascular Data Registry in the US showed that extremely obese patients had higher in-hospital mortality, we believe that it has the same trend in elderly patients. Third, the sample size was still limited, which restricted the statistical power in discriminating the differences. Finally, the secondary endpoint was defined as the incidence rate of 1 year death. However, changes in BMI after patients’ discharge were not measured. Previous study suggested that patients with higher BMIs were more aware of CAD, and more willing to adapt lifestyle and taking drugs. This could affect the comparison of 1 year outcomes between the groups.
Elderly patients of underweight, normal weight, overweight and obese had similar in-hospital MACE after PCI. The “obesity paradox” should be interpreted with caution, thus BMI may not be a sensitive predictor of cardiovascular events in elderly patients.
1. Calle EE, Thun MJ, Petrelli JM, Rodriguez C, Heath CW Jr. Body-mass index and mortality in a prospective cohort of U.S. adults N Engl J Med. 1999;341:1097–105
2. Wilson PW, D’Agostino RB, Sullivan L, Parise H, Kannel WB. Overweight and obesity as determinants of cardiovascular risk: The Framingham experience Arch Intern Med. 2002;162:1867–72
3. Gruberg L, Weissman NJ, Waksman R, Fuchs S, Deible R, Pinnow EE, et al The impact of obesity on the short-term and long-term outcomes
after percutaneous coronary intervention: The obesity paradox? J Am Coll Cardiol. 2002;39:578–84
4. Minutello RM, Chou ET, Hong MK, Bergman G, Parikh M, Iacovone F, et al Impact of body mass index
on in-hospital outcomes
following percutaneous coronary intervention (report from the New York State Angioplasty
Registry) Am J Cardiol. 2004;93:1229–32
5. Sarno G, Räber L, Onuma Y, Garg S, Brugaletta S, van Domburg RT, et al Impact of body mass index
on the five-year outcome of patients having percutaneous coronary interventions with drug-eluting stents Am J Cardiol. 2011;108:195–201
6. Park DW, Kim YH, Yun SC, Ahn JM, Lee JY, Kim WJ, et al Association of body mass index
with major cardiovascular events and with mortality after percutaneous coronary intervention Circ Cardiovasc Interv. 2013;6:146–53
7. Kaneko H, Yajima J, Oikawa Y, Tanaka S, Fukamachi D, Suzuki S, et al Obesity paradox in Japanese patients after percutaneous coronary intervention: An observation cohort study J Cardiol. 2013;62:18–24
8. Tarastchuk JC, Guérios EE, Bueno Rda R, Andrade PM, Nercolini DC, Ferraz JG, et al Obesity and coronary intervention: Should we continue to use body mass index
as a risk factor? Arq Bras Cardiol. 2008;90:284–9
9. Mehran R, Rao SV, Bhatt DL, Gibson CM, Caixeta A, Eikelboom J, et al Standardized bleeding definitions for cardiovascular clinical trials: A consensus report from the Bleeding Academic Research Consortium Circulation. 2011;123:2736–47
10. Nikolsky E, Stone GW, Grines CL, Cox DA, Garcia E, Tcheng JE, et al Impact of body mass index
after primary angioplasty
in acute myocardial infarction Am Heart J. 2006;151:168–75
11. Mehta L, Devlin W, McCullough PA, O’Neill WW, Skelding KA, Stone GW, et al Impact of body mass index
after percutaneous coronary intervention in patients with acute myocardial infarction Am J Cardiol. 2007;99:906–10
12. Vlaar PJ, Lennon RJ, Rihal CS, Singh M, Ting HH, Bresnahan JF, et al Drug-eluting stents in octogenarians: Early and intermediate outcome Am Heart J. 2008;155:680–6
13. Diercks DB, Roe MT, Mulgund J, Pollack CV Jr, Kirk JD, Gibler WB, et al The obesity paradox in non-ST-segment elevation acute coronary syndromes: Results from the can rapid risk stratification of unstable angina patients suppress ADverse outcomes
with early implementation of the American College of Cardiology/American Heart Association Guidelines Quality Improvement Initiative Am Heart J. 2006;152:140–8
14. Steinberg BA, Cannon CP, Hernandez AF, Pan W, Peterson ED, Fonarow GC. Medical therapies and invasive treatments for coronary artery disease by body mass: The “obesity paradox” in the get with the guidelines database Am J Cardiol. 2007;100:1331–5
15. Shubair MM, Prabhakaran P, Pavlova V, Velianou JL, Sharma AM, Natarajan MK. The relationship of body mass index
after percutaneous coronary intervention J Interv Cardiol. 2006;19:388–95
16. Newell MC, Henry JT, Henry TD, Duval S, Browning JA, Christiansen EC, et al Impact of age on treatment and outcomes
in ST-elevation myocardial infarction Am Heart J. 2011;161:664–72
17. Romero-Corral A, Montori VM, Somers VK, Korinek J, Thomas RJ, Allison TG, et al Association of bodyweight with total mortality and with cardiovascular events in coronary artery disease: A systematic review of cohort studies Lancet. 2006;368:666–78
18. Li TY, Rana JS, Manson JE, Willett WC, Stampfer MJ, Colditz GA, et al Obesity as compared with physical activity in predicting risk of coronary heart disease in women Circulation. 2006;113:499–506
19. Wellens RI, Roche AF, Khamis HJ, Jackson AS, Pollock ML, Siervogel RM. Relationships between the Body Mass Index
and body composition Obes Res. 1996;4:35–44
20. Romero-Corral A, Somers VK, Sierra-Johnson J, Jensen MD, Thomas RJ, Squires RW, et al Diagnostic performance of body mass index
to detect obesity in patients with coronary artery disease Eur Heart J. 2007;28:2087–93
21. Yusuf S, Hawken S, Ounpuu S, Bautista L, Franzosi MG, Commerford P, et al Obesity and the risk of myocardial infarction in 27,000 participants from 52 countries: A case-control study Lancet. 2005;366:1640–9
22. Payvar S, Kim S, Rao SV, Krone R, Neely M, Paladugu N, et al In-hospital outcomes
of percutaneous coronary interventions in extremely obese and normal-weight patients: Findings from the NCDR (National Cardiovascular Data Registry) J Am Coll Cardiol. 2013;62:692–6
23. Andreotti F, Rio T, Lavorgna A. Body fat and cardiovascular risk: Understanding the obesity paradox Eur Heart J. 2009;30:752–4
Edited by: Yi Cui
Source of Support: This work was supported by 2014 Special fund for scientific research in the public interest by National Health and Family Planning Commission of the People's Republic of China (No. 201402001).
Conflict of Interest: None declared.