In the United States, 97 million overweight or obese

The Risks of Moderate and Extreme Obesity for Coronary Artery Bypass Grafting Outcomes: A Study From The Society of Thoracic Surgeons Database Ganga Prabhakar, MD, Constance K. Haan, MD, Eric D. Peterson, MD, MPH, Laura P. Coombs, PhD, Jose L. Cruzzavala, MD, and Gordon F. Murray, MD West Virginia University, Morgantown, West Virginia Background. Obesity is epidemic in the United States and afflicts 97 million adults. Prior single center studies have been contradictory as to obese patients having higher risks with coronary artery bypass operations. Our objective was to assess the independent effect of both moderate (body mass index [BMI], 35 to 39.9) and extreme (BMI > 40) obesity on bypass operation outcomes using the Society of Thoracic Surgeons National Cardiac Database. Methods. The study population consisted of 559,004 patients from the Society of Thoracic Surgeons database who underwent first-time, isolated coronary artery bypass grafting between January 1997 and December 2000. We compared 42,060 moderately obese patients (BMI, 35 to 39.9) and 18,735 extremely obese patients (BMI > 40) with 498,209 normal or mildly obese patients (BMI, 18.5 to 34.9). Multivariable logistic regression was used to determine whether BMI subgroups were independent predictors of operative risk after adjusting for other preoperative factors. Results. Compared with normal or mildly obese patients (BMI, 18.5 to 34.9), moderate and severely obese patients were younger and more likely to be diabetic and hypertensive. After adjusting for these and other known preoperative risk factors, moderate obesity slightly elevated patients operative risk (adjusted odds ratio, 1.21; confidence interval, 1.13 to 1.29). In contrast, extremely obese patients had marked higher risk for operative mortality (adjusted odds ratio, 1.58; confidence interval, 1.45 to 1.73). Major perioperative complications, particularly deep sternal wound infection, renal failure, and prolonged postoperative hospital stay also increased for extremely obese patients. Conclusions. Extreme obesity (body mass index > 40) is a significant independent predictor for adverse outcomes and prolonged hospitalization after coronary artery bypass operation. (Ann Thorac Surg 2002;74:1125 31) 2002 by The Society of Thoracic Surgeons In the United States, 97 million overweight or obese adults pose a major public health challenge. Obesity is a known risk factor not only for heart disease, but also for diabetes, hypertension, stroke, and certain forms of cancer [1]. This obese patient population is at a 50% to 100% increased risk of all-cause death than their counterparts of the same age. Although cardiac operations in obese patients have been studied and are generally considered safe [2], there are conflicting conclusions to the studies. The published studies have limitations that include small sample sizes, varied definitions of obesity, and inclusion of very few patients at the high end of the obesity scale [3 5]. The largest study to date is comprised of 11,101 patients from the Northern New England Cardiovascular Disease Study Group, and found that obesity did not Presented at the Thirty-eighth Annual Meeting of The Society of Thoracic Surgeons, Fort Lauderdale, FL, Jan 28 30, 2002. Address reprint requests to Dr Murray, Dept of Surgery, PO Box 9238, HSC North, Morgantown WV 26506; e-mail: gmurray@hsc.wvu.edu. significantly increase postoperative complications apart from sternal wound infection [6]. Our current study re-examines this question of obesity using the Society of Thoracic Surgeons (STS) database. This database s large sample size provides the ability to examine cardiac surgical risks in several obesity subgroups. Material and Methods From January 1997 to December 2000, 631,169 isolated primary coronary artery bypass graft patients were entered into the STS database and formed the basis of this study. Patients with prior coronary artery bypass grafts were excluded from the analysis. Patients for whom height or weight was not available were also excluded. The remaining 559,004 patients formed the basis for the present study. Preoperative patient characteristics included age, gender, chronic lung disease, history of diabetes, hypertension, renal failure, cerebrovascular accident, cardiac function, myocardial infarction, and extent of coronary artery disease (Table 1). The intraoper- 2002 by The Society of Thoracic Surgeons 0003-4975/02/$22.00 Published by Elsevier Science Inc PII S0003-4975(02)03899-7

1126 PRABHAKAR ET AL Ann Thorac Surg RISKS OF OBESITY FOR CABG OUTCOMES 2002;74:1125 31 Table 1. Patient Characteristics by Obesity Groups Variable Normal to Mild Obesity (Body Mass Index, 18.5 34.9) (n 498,209) Moderate Obesity (Body Mass Index, 35 39.9) (n 42,060) Extreme Obesity (Body Mass Index 40) (n 18,735) Average predicted.027.022.022 mortality Age (y) Mean 65.4 60.9 59.2 25th/50th/75th 58/67/74 53/61/69 52/59/67 Percentile Female (%) 27.9 38.3 47.5 Chronic lung disease (%) Yes 14.3 15.4 16.7 Diabetes (%) Yes 30.9 48.2 54.3 Hypertension (%) Yes 66.8 78.1 78.8 Renal failure (%) Yes 4.5 4.4 4.6 Cerebrovascular accident 6.7 6.0 5.8 (%) Ejection fraction (%) Mean 50.8 51.0 50.8 Myocardial infarction % 24 hours 3.0 2.7 2.5 1 7 days 15.9 15.4 15.2 7 days 24.5 25.0 24.5 Left-main coronary 21.4 18.7 18.9 artery (%) Triple vessel disease (%) 67.5 66.1 64.3 ative variables included urgency of the operation, use of intraaortic balloon pump, perfusion time, cross-clamp time, use of internal mammary artery, and number of grafts (Table 2). The patient population was studied for operative mortality, stroke, renal failure, deep sternal infection, prolonged ventilation, reoperation for any reason, and postoperative hospital length of stay. Obesity was assessed using body mass index (BMI), which describes relative weight for height and correlates significantly with total body fat content. The BMI is calculated as weight (kg)/height squared (m 2 ). The weight classification for this study was performed using the National Institutes of Health guidelines with normal BMIs of 18.5 to 24.9, mild obesity BMIs of 25 to 34.9, moderate obesity BMIs of 35 to 39.9, and extreme obesity BMIs 40 [1]. Mild obesity has become prevalent and formed the majority of patients undergoing coronary artery bypass grafting; it was therefore combined with Table 2. Intraoperative Variables in the Obesity Groups Variable Normal to Mild Obesity (Body Mass Index, 18.5 34.9) Moderate Obesity (Body Mass Index, 35 39.9) Extreme Obesity (Body Mass Index 40) Status Elective 60.6 62.3 61.4 Urgent 32.4 31.7 32.2 Emergent 5.8 4.9 5.2 Salvage 0.5 0.4 0.5 Intraaortic balloon pump (%) None 91.0 91.3 91.8 Preoperative 6.6 6.2 6.0 Intraoperative 1.7 1.7 1.5 Postoperative 0.7 0.7 0.7 Perfusion time (min) Mean 97.0 98.9 98.6 25th/50th/75th 72/92/117 73/94/119 72/94/119 Percentile X-clamp time (min) Mean 64.2 65.1 64.8 25th/50th/75th Percentile 44/60/79 45/61/80 44/61/80 Internal mammary artery used (%) None 15.4 13.7 17.1 Unilateral 80.7 83.3 80.8 Bilateral 3.9 3.0 2.1 Number of grafts (%) 1 7.4 7.8 9.2 2 13.9 14.9 16.0 3 31.2 31.8 32.1 4 44.6 42.8 39.6

Ann Thorac Surg PRABHAKAR ET AL 2002;74:1125 31 RISKS OF OBESITY FOR CABG OUTCOMES 1127 Table 3. Unadjusted Outcomes by Obesity Groups Variable Normal to Mild Obesity (Body Mass Index, 18.5 34.9) Moderate Obesity (Body Mass Index, 35 39.9) Extreme Obesity (Body Mass Index 40) p Value Number (n) n 498,209 n 42,060 n 18,735 Operative mortality (%) 2.6 2.5 3.1 0.0001 Stroke (%) 1.7 1.3 1.3 0.0001 Renal failure (%) 3.4 4.4 5.0 0.0001 Prolonged ventilation (%) 5.6 7.1 7.9 0.0001 Deep sternal infection (%) 0.5 1.2 1.8 0.0001 Any reoperation (%) 5.1 4.7 4.9 0.0001 Mortality or any morbidity (%) 12.7 14.1 15.8 0.0001 Postoperative length of stay (d) Mean 6.8 7.1 7.7 0.0001 Median 5.0 5.0 6.0 25th 4.0 4.0 5.0 75th 7.0 7.0 8.0 the normal BMI group to allow comparison with the higher ends of the obesity scale (moderate and extreme obesity). Unadjusted mortality and morbidity rates were calculated and differences between the three BMI groups were tested using 2 tests. To make risk-adjusted comparisons, the risk factors (excluding body surface area) contained in the multivariable logistic regression models recently developed by the STS for mortality, five major morbidities, prolonged length of stay, and the combined outcome of mortality or major morbidity were used. Variables representing moderate and extreme obesity were then added to each model. Odds ratios and 95% confidence intervals for the BMI groups were calculated to determine whether obesity was an independent predictor of outcome. Finally we examined interactions between BMI and age and gender. The interaction was examined both graphically and by adding interaction terms to the multivariable logistic regression models. Results Of the 559,004 patients, 42,060 (7.5%) had moderate obesity (BMIs, 35 to 39.9) and 18,735 (3.4%) had extreme obesity (BMIs 40). Men formed 66.9% of the normal to mild BMI population, 61.7% of the moderate BMI group, and 52.5% of the BMI 40 group as shown in Table 1. The distribution of other risk factors for the three BMI groups is also provided in the table. Obese patients appeared to undergo operations at a younger age, but had a higher frequency of hypertension, and were more often diabetic. The preoperative incidence of cerebrovascular accident was slightly higher, and chronic lung disease slightly lower, whereas renal failure was similar. The preoperative ejection fraction and myocardial infarction rate in each group were essentially identical. The operative status (elective vs urgent or emergent) was similar for the three groups, as was perioperative use of the intraaortic balloon pump (Table 2). The extremely obese group had a slightly higher frequency of use of single and double graft procedures, whereas at the same time they had comparable cross-clamp and perfusion times. There was little difference in use of the internal mammary artery in the three groups studied; however, bilateral mammary artery use was notably higher in the normal and mildly obese subgroup. The unadjusted operative mortality rates were highest among patients with extreme obesity 3.1% versus 2.6% for the normal to mild obesity group and 2.5% for the moderate obesity group (Table 3). Unadjusted rates of stroke and reoperation were actually highest among those with normal to mild obesity patients relative to extreme obesity patients. On the other hand, rates of renal failure, prolonged ventilation, and deep sternal wound infection progressively increased as BMI increased, achieving statistical significance. Risk-adjusted outcomes are presented in Table 4. Riskadjusted odds ratios show an increase in risk of mortality for patients with moderate obesity (adjusted odds ratio [OR], 1.21; 95% confidence interval [CI], 1.13 to 1.29) and a higher risk of mortality for the extremely obese (OR, 1.58; CI, 1.45 to 1.73). Increasing obesity also resulted in higher risks of reoperation, renal failure, prolonged ventilation, and deep sternal wound infection after adjusting for other risk factors. In addition, both moderately and extremely obese patients were more likely to have postoperative hospital stays of more than 14 days. Figure 1 displays the continuous relationship between BMI and risk-adjusted mortality for both female and male patients. Although women had generally higher risk than males across the entire range of BMI, the general U-shaped relationship between BMI and outcome were fairly similar in both male and female patients. The relationship between BMI and risk-adjusted operative mortality was also similar in young patients ( 75 years old) versus older patients ( 75 years old) (Fig 2). Against the comparison group of normal and mildly obese patients younger than 75 years of age, patients younger than 75 years of age with a BMI 40 had adjusted OR for operative mortality of 1.42 (95% CI, 1.30 to 1.56). In patients older than 75 years of age, extreme

1128 PRABHAKAR ET AL Ann Thorac Surg RISKS OF OBESITY FOR CABG OUTCOMES 2002;74:1125 31 Table 4. Adjusted Odds Ratios and 95% Confidence Intervals a by Obesity Groups Outcome Odds Ratio (Body Mass Index 35 39.9) 95% Confidence Interval Odds Ratio (Body Mass Index 40) 95% Confidence Interval Operative mortality 1.21 1.13 1.29 1.58 1.45 1.73 Stroke 0.91 0.83 0.99 0.94 0.83 1.07 Renal failure 1.58 1.50 1.67 1.92 1.79 2.07 Prolonged ventilation 1.49 1.42 1.55 1.70 1.61 1.81 Deep sternal infection 2.22 2.01 2.45 3.15 2.79 3.55 Reoperation 1.04 0.99 1.09 1.11 1.03 1.19 Mortality or any morbidity 1.30 1.26 1.34 1.53 1.46 1.59 Length of stay 14 d 1.37 1.31 1.44 1.78 1.67 1.89 a Comparison group is body mass index of 18.5 34.9. obesity was somewhat rare, but still resulted in a trend toward higher adjusted OR for operative mortality relative to those with normal or mild obesity, adjusted OR of 1.15 (95% CI, 0.91 to 1.45). Comment Obesity is a national epidemic and its prevalence has increased by more than 50% from the 1960s with most of the rise occurring over the last decade. This rise in obesity affected every state of the United States, both genders, and included all races or ethnicities, age groups, and educational levels [7]. The increased emphasis on exercise, diet, and risk factor modification has not resulted in a significant decrease of obesity. As noted, there has been, in fact, a steady increase in the prevalence of obesity. The direct cost of obesity is $51.6 billion of which $6.99 billion applies to cardiac costs, forming 17% of the total direct cost of heart disease [7]. Obesity is a widely recognized risk factor for coronary artery disease, diabetes, stroke, hypertension, and certain cancers [1]. Obese individuals have been shown to have a 50% to 100% increased risk of death from all causes (mostly cardiovascular) compared with normal individuals [7, 8]. Altered pulmonary functions result from an increase in functional residual capacity and a decrease in vital capacity and maximum voluntary ventilation [5]. These factors have led to the presumption that obese individuals are at a higher risk for operative mortality and morbidity. However, this presumption has not been previously proven, despite a number of studies examining the influence of obesity on cardiac operations. Whereas low BMI ( 20) has been related to increased mortality, renal failure, pneumonia, and reoperation for bleeding [9, 10], high BMI has not been shown to be at a higher risk in previous publications [6, 9, 11]. For example, the Northern New England Cardiovascular Disease Study Group reported that obesity was not associated with increased operative mortality or cerebrovascular accidents [6]. In our larger study, moderate obesity was associated with a slight but statistically significant increase in riskadjusted increase in mortality (OR, 1.21; CI, 1.13 to 1.29) and those with extreme obesity had nearly a 50% increase in risk-adjusted mortality (Table 4). This high mortality risk for those with extreme obesity has not been evident Fig 1. Graph of the effect of body mass index (BMI) on mortality by gender shows a consistently higher risk for females across all levels of BMI. Fig 2. Graph of the effect of body mass index (BMI) on mortality by age group shows that patients older than 75 years of age have a higher risk of mortality than patients younger than 75 years of age, regardless of BMI.

Ann Thorac Surg PRABHAKAR ET AL 2002;74:1125 31 RISKS OF OBESITY FOR CABG OUTCOMES 1129 in previous studies because of the small number of subjects with BMI of more than 40. The incidence of cerebrovascular accidents was similar in both the obese and nonobese groups, which mirrored other reported studies [6, 9]. However, in contrast to previous publications, we found the incidence of renal failure increased markedly with increasing size of the patient (relative risk of 1.58 in the moderately obese and 1.92 in the extremely obese). The reason for the increased risk of renal failure is not entirely clear. The higher incidence of hypertension and diabetes in these patients could explain this exaggerated risk, with operations unmasking the renal dysfunction. The cardiopulmonary bypass times were not significantly longer in the obese patients. Further studies evaluating renal function in a prospective manner would be needed to better understand this higher incidence of renal failure. Prolonged periods of ventilation were also seen in patients of both obesity subgroups (7.1% and 7.9% compared with 5.6% in the normal and mildly obese subgroup). This could contribute to the slightly increased length of postoperative hospital stay in the extremely obese group. Sternal wound complications have been higher for obese patients after cardiac operations according to most studies [2, 6, 12], but not all studies [2]. This higher incidence of wound complications has been seen in both superficial and deep sternal wounds, as well as leg wound incisions. For example, Prasad and colleagues [4] study compared 250 obese patients with 250 control patients, which showed an incidence of 9.2% of deep sternal infections for the obsese patients versus 2.8% for the nonobese. In Birkmeyer and colleagues [6] study, the incidence of deep sternal wound infection was shown to be higher in obese patients and was associated with age, renal failure, diabetes, chronic obstructive pulmonary disease, bilateral internal mammary artery grafting, and cardiopulmonary bypass time. Kouchoukos and colleagues [13] also identified bilateral internal mammary artery bypass grafting, obesity, and prolonged mechanical ventilation as significant risk factors for sternal infections by multivariate logistic regression analysis. Prolonged operative time in obese patients was also thought to have contributed to the higher incidence of wound complications [14]. In our patients the relative risk of deep sternal infections was 2.22 (95% CI, 2.01 to 2.45) in moderately obese patients and rose to 3.15 (95% CI, 2.79 to 3.55) in extremely obese patients. Of interest, the cardiopulmonary bypass times and cross-clamp times were nearly identical in the three subgroups. The use of internal mammary arteries was identical in the normal and obese groups in our study. Bilateral internal mammary artery harvesting was undertaken slightly less often in the obese groups (2.1% to 3.0%) in comparison with the normal BMI population (3.9%). Leg incision complications were difficult to elucidate from the STS database because most of them occurred after hospital discharge. Study Limitations Whereas the current study sheds light on the problem of coronary artery bypass grafting in the obese patient, there are limitations. First, calculating BMI as an indicator of obesity is simple, quick, and inexpensive, but it does have its shortcomings. Very muscular people may fall into the overweight category when they are actually fit, and some of the elderly may fall into the normal weight category after losing muscle mass [7]. Second, participation in the STS database is voluntary, which causes possible concern of underreporting of adverse events. The STS assures strict confidentiality, and a comparison of results from the STS database with those in audited databases revealed similar risk factor profiles and mortality and morbidity rates. Third, this is an observational analysis, so there may be concerns of selection bias. Although we have adjusted for patient level risk factors, we cannot account for possible surgeon bias in referring obese patients to surgical treatment. Finally, this study does not evaluate the morbidity that occurs after the patients are discharged from the hospital. For example, it is known that 14% of the patients can be re-hospitalized after hospital discharge [6]. There are a paucity of data both on long-term concerns of coronary artery disease and on long-term outcomes after coronary artery bypass operations in obese patients, and these have not been addressed in the present study. Prasad and colleagues [4] has previously shown a 14.9% recurrence of angina at 12 months with a majority of the 250 obese patients in the study with BMIs of 25 to 40. These authors speculate that this was a result of increased myocardial oxygen demand and more associated risk factors. Schwann and colleagues [10] showed that the 5-year survival in obese patients was worse despite them being younger. Conclusion In conclusion, the proportion of moderately and extremely obese patients requiring coronary artery bypass grafting is about 11%. The relative risks of coronary artery bypass grafting for patients with moderate obesity was slightly higher than in patients with normal or mildly increased BMI, but the risk increase was quite small in terms of absolute risk. In contrast, extreme obesity significantly increased mortality and morbidity after coronary artery operations by more than 50%. For example, a typical patient with mild obesity may have an expected mortality of 3.0%. A patient with similar risk factors but moderate obesity would have an expected mortality of 3.4%, whereas extreme obesity would result in an expected mortality of 4.7%. From a health policy perspective, aggressive interventions are needed nationally to alleviate the epidemic of obesity in the United States. This would both diminish progression of coronary artery disease and bypass operative risk when needed. In addition, methods to decrease cardiac surgical morbidity and mortality must be studied. Whether better patient selection, early ambulation, and

1130 PRABHAKAR ET AL Ann Thorac Surg RISKS OF OBESITY FOR CABG OUTCOMES 2002;74:1125 31 methods to improve postoperative respiratory mechanics will alter this remains to be demonstrated. Finally, the long-term benefits of myocardial revascularization in obese patients need to be examined in a careful prospective study. The authors thank Mary Eiken, National Database Director for The Society of Thoracic Surgeons, whose help and coordination made this study possible. References 1. National Institutes of Health. Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults. National Heart, Lung and Blood Institute. June 1998. 2. Moulton M, Creswell LL, Mackey ME, Cox JL, Rosenbloom M. Obesity is not a risk factor for significant adverse outcomes after cardiac surgery. Circulation 1996;94(Suppl II): II87 92. 3. Brandt M, Harder K, Walluscheck KP, et al. Severe obesity does not adversely affect perioperative mortality and morbidity in coronary artery bypass surgery. Eur J Cardiothorac Surg 2001;19:662 6. 4. Prasad US, Walker WS, Sang CTM, Campanella C, Cameron EWJ. Influence of obesity on the early and long term results of surgery for coronary artery disease. Eur J Cardiothorac Surg 1991;5:67 73. 5. Koshal A, Hendry P, Raman SV, Keon WJ. Should obese patients not undergo coronary artery surgery? Can J Surg 1985;28:331 4. 6. Birkmeyer NJO, Charlesworth DC, Hernandez F, et al. Obesity and risk of adverse outcomes associated with coronary artery bypass surgery. Circulation 1998;97:1689 94. 7. National Institutes of Diabetes and Digestive and Kidney Diseases. Statistics related to overweight and obesity. NIH Publ No 96 4158. Update June 2000. 8. Hubert HB, Feinleib M, McNamara PM, Castelli WP. Obesity as an independent risk factor for cardiovascular disease: 26-year follow-up of participants in the Framingham study. Circulation 1983;67:968 77. 9. Engelman DT, Adams DH, Byrne JG, et al. Impact of body mass index and albumin on morbidity and mortality after cardiac surgery. J Thorac Cardiovasc Surg 1999;118:866 73. 10. Schwann TA, Habib RH, Zacharias A, et al. Effects of body size on operative, intermediate and long-term outcomes after coronary artery bypass operation. Ann Thorac Surg 2001;71:521 31. 11. Rohs T Jr, Polanski P, Just SC, Gordon W, Just-Viera JO. Early complications and long-term survival in severely obese coronary bypass patients. Am Surg 1995;61:949 53. 12. Fasol R, Schindler M, Schumacher B, et al. The influence of obesity on perioperative morbidity: retrospective study of 502 aortocoronary bypass operations. Thorac Cardiovasc Surg 1992;40:126 9. 13. Kouchoukos NT, Wareing TH, Murphy SF, Pelate C, Marshall WG. Risks of bilateral internal mammary artery bypass grafting. Ann Thorac Surg 1990;49:210 9. 14. Loop FD, Lytle BW, Cosgrove DM, et al. Sternal wound complications after isolated coronary artery bypass grafting: early and late mortality, morbidity, and cost of care. Ann Thorac Surg 1990;49:179 87. DISCUSSION DR FRED H. EDWARDS (Jacksonville, FL): I would like to thank The Society for the privilege of discussing this article and I also would like to thank the authors for providing the article in advance of the meeting. Probably most of us have the subjective impression that an obese patient is not just going to fare as well after a heart operation as compared with a nonobese patient. But surprisingly, that impression has been difficult to verify when you look at objective studies. As the authors point out, most previous studies have shown no significant difference at all in operative mortality. There have been some drawbacks, though, in these previous investigations, most notably the small patient populations, and the work presented today of course obviates that by evaluating the enormous experience contained in The Society of Thoracic Surgeons (STS) database. Using the statistical power associated with these larger numbers, the authors have shown a significant increase in operative mortality for the extremely obese patient. This represents new and, I think, very useful clinical information. I do have three questions, though, that perhaps can help us better understand the important work that has been presented today. First, sometimes these mortality differences can be confined to different parts of the risk spectrum. For example, several years ago when the STS took a look at the impact of gender on coronary bypass operative morality, we found that the women had a higher risk of death only in the low and moderate risk categories. When we looked at high-risk patients, there was no difference between men and women undergoing bypass operations. Now these extremely obese patients also cover a spectrum of operative risk, from the very low-risk patient up to the patient at very high risk, and that, of course, can be very easily determined using the STS mortality models. That leads to the first question. Did these extremely obese patients have an increased mortality in all parts of the risk spectrum, or, as with our gender study, only in specific risk categories? Second, you used arbitrary National Institutes of Health (NIH) guidelines to classify the patients into body mass index (BMI) groups, and that certainly is fair enough, but it would be useful to know if the data defined any natural break points. In other words, did the data identify any BMI values that seemed to separate those patients having complications from those that tended to be free of complications? Last, I would appreciate your comments on the practical implications of your study. Should we change our approach to patients having a BMI greater than 40? Specifically, was there a particularly high risk subset of obese patients that perhaps should not be offered bypass operations? Again, I would like to congratulate the authors for a very fine presentation and I thank the Society for the privilege of discussing the article. DR GIORGIO M. ARU (Jackson, MS): What about the pulmonary embolism? It has been our feeling that a patient with a large body mass, and especially a female, has a much higher incidence of pulmonary embolism; and some of the deaths are actually related to pulmonary embolism. DR PRABHAKAR: Thank you for those comments. To address the questions that Dr Edwards raised with regards to risk categorization, we did not look further into the BMI categories

Ann Thorac Surg PRABHAKAR ET AL 2002;74:1125 31 RISKS OF OBESITY FOR CABG OUTCOMES 1131 greater than 40. We divided them purely by the NIH guidelines, because most publications seemed to be based on that. It would certainly be interesting to look and subclassify the BMI greater than 40. In terms of changing strategy with BMI greater than 40, I think all of us have consciously or subconsciously already changed the strategy over many years in that we seem to be choosing younger patients, as well as those with lower risk factors, and that is what is keeping the mortality low. I think if we blinded ourselves to other risk factors, I suspect the mortality would be considerably more than has been shown today. So I think all of us are already pre-selecting patients. What is also important noting is that when patients with BMI greater than 40 were followed over the intermediate or long term, almost 20% of them developed angina in the first1to2 years. We do not have any long-term results. So I think it is certainly worth following up these patients over the long term to see, one, whether we should be operating; two, what we should be doing differently; and three, how we should be selecting the patients better. Unless we have more long-term results, I think it will be hard to do any more selection than we are already doing. I think we are fortunate in having the results we have today. The pulmonary embolic rates in The Society of Thoracic Surgeons database are very similar for all BMI categories. I know there are one or two other studies that show that the pulmonary embolic rate is higher, but in the STS database there is no difference in the pulmonary embolic rate based on clinical criteria that are used in the database. Thank you.