The purpose of this study was to assess the impact of body mass index (BMI) on clinical outcome of patients treated by percutaneous coronary intervention (PCI) using drug-eluting stents. Patients were stratified according to BMI as normal (<25 kg/m 2 ), overweight (25 to 30 kg/m 2 ), or obese (>30 kg/m 2 ). At 5-year follow-up all-cause death, myocardial infarction, clinically justified target vessel revascularization (TVR), and definite stent thrombosis were assessed. A complete dataset was available in 7,427 patients, of which 45%, 22%, and 33% were classified according to BMI as overweight, obese, and normal, respectively. Mean age of patients was significantly older in those with a normal BMI (p <0.05). Incidence of diabetes mellitus, hypertension, and dyslipidemia increased as BMI increased (p <0.05). Significantly higher rates of TVR (15.3% vs 12.8%, p = 0.02) and early stent thrombosis (1.5% vs 0.9%, p = 0.04) were observed in the obese compared to the normal BMI group. No significant difference among the 3 BMI groups was observed for the composite of death/myocardial infarction/TVR or for definite stent thrombosis at 5 years, whereas the normal BMI group was at higher risk for all-cause death at 5 years (obese vs normal BMI, hazard ratio 0.74, confidence interval 0.53 to 0.99, p = 0.05; overweight vs normal BMI, hazard ratio 0.73, confidence interval 0.59 to 0.94, p = 0.01) in the multivariate Cox proportional hazard model. Age resulted in a linearly dependent covariate with BMI in the all-cause 5-year mortality multivariate model (p = 0.001). In conclusion, the “obesity paradox” observed in 5-year all-cause mortality could be explained by the higher rate of elderly patients in the normal BMI group and the existence of colinearity between BMI and age. However, obese patients had a higher rate of TVR and early stent thrombosis and a higher rate of other risk factors such as diabetes mellitus, hypertension, and hypercholesterolemia.
The purpose of this study was to assess the impact of body mass index (BMI) on 5-year clinical outcome of patients treated by percutaneous coronary intervention (PCI) with a sirolimus-eluting stent (SES) or paclitaxel-eluting stent (PES) in a large 2-institution cohort study in which rates of early and late stent thromboses have been extensively documented.
From April 2002 through December 2005, 8,146 consecutive patients underwent PCI with the 2 drug-eluting stent types approved by the Food and Drug Administration at 2 academic referral hospitals in Switzerland and the Netherlands; 3,823 patients were treated with SESs (Cypher, Cordis Corporation, Johnson & Johnson, Warren, New Jersey) and 4,323 patients were treated with PESs (TAXUS Express or Liberté, Boston Scientific, Natick, Massachusetts). Use of the respective stent platforms at the 2 institutions has been reported previously. For the present 5-year follow-up, patients were contacted 1 year after the last contact with specific questions from a health questionnaire addressing repeat hospital stay and major adverse cardiac events. Patients who did not return the questionnaire were contacted by telephone, at which time the questionnaire was completed. Moreover, survival data were obtained from municipal civil registries. If necessary, medical records and discharge summaries from other institutions were systematically reviewed and primary care physicians were contacted for additional or missing information. The common database was held and analysed at the Thoraxcenter, Erasmus University Hospital. The study was approved by the local ethics committee in the 2 hospitals and is in accordance with the Declaration of Helsinki. Written informed consent was obtained from all patients.
The National Heart, Lung, and Blood Institute and the World Health Organization have introduced a weight classification for BMI that is calculated by dividing a patient’s weight in kilograms by that patient’s height in meters squared. According to this classification, a BMI of 18.5 to 24.9 kg/m 2 is considered normal, a BMI of 25 to 30 kg/m 2 is considered overweight, and a BMI >30 kg/m 2 is considered obese. Patients enrolled in the study were stratified into 3 subgroups according to their BMI: normal (BMI 18.5 to 24.9 kg/m 2 ), overweight (BMI 25 to <30 kg/m 2 ), and obese (BMI >30 kg/m 2 ).
Definite stent thrombosis was defined as presence of Thrombolysis In Myocardial Infarction grade 0 flow with occlusion originating in the peri-stent region or grade 1 and 2 or 3 flow in the presence of a thrombus originating in the peri-stent region. Angiographic evidence of thrombus was defined as a discrete intraluminal filling defect with defined borders and separated from the vessel wall. Moreover, ≥1 of the following criteria had to be met: (1) acute ischemic symptoms (typical chest pain with duration ≥20 minutes); (2) ischemic electrocardiographic changes in ST-segment elevation in the territory of the implanted stent; (3) ST-segment depression or T-wave inversion in the territory of the implanted stent; or (4) typical increase and decrease in cardiac biomarkers.
All cases of definite stent thrombosis were reviewed independently by 2 experienced interventional cardiologists; for disagreement, a consensus was established between the 2 reviewers or a third interventional cardiologist was consulted. Moreover, stent thrombosis was categorized as early (within 30 days), late (≥30 to ≤365 days), and very late (>365 days) depending on the timing of the occurrence of the event.
Diagnosis of myocardial infarction was based on the presence of new Q waves in ≥2 contiguous leads with an increased creatinine kinase-MB fraction. In the absence of pathologic Q waves, diagnosis of myocardial infarction was based on an increase in creatinine kinase to >2 times the upper limit of normal with an increased creatinine kinase-MB fraction of >3 times the upper limit of normal.
Target vessel revascularization (TVR) was defined as any repeat PCI or surgical bypass of any segment within the entire major coronary vessel proximal and distal to a target lesion including upstream and downstream branches and the target lesion itself. Revascularization was regarded as clinically justified if the stenosis of the treated lesion was ≥50% of lumen diameter based on quantitative coronary angiogram in the presence of ischemic signs or symptoms or if diameter stenosis was ≥70% irrespective of the presence or absence of ischemic signs or symptoms.
Premature discontinuation of antiplatelet therapy was referred to as cessation of acetylsalicylic acid and/or clopidogrel before the recommended duration of prescription. A creatinine value ≥150 μmol or long-term hemodialysis was defined as renal impairment.
All interventions were performed according to current practice guidelines for PCI. The decision to choose a specific treatment strategy was left to the discretion of the operator. Patients were prescribed acetylsalicylic acid 100 mg 1 time/day plus clopidogrel 75 mg/day (after a loading dose of 300 or 600 mg) before or during baseline coronary interventions. After the procedure, all patients were advised to maintain lifelong acetylsalicylic acid 100 mg 1 time/day.
In the Swiss institution, 12 months of clopidogrel therapy was prescribed irrespective of stent type used. In the Dutch institution, PES-treated patients received ≥6 months of clopidogrel (75 mg/day), whereas patients treated with SESs were prescribed clopidogrel for ≥3 months unless 1 of the following was present (when clopidogrel was maintained for ≥6 months): ≥3 SES implantations, total stent length ≥36 mm, long-term total occlusion, and bifurcations. In a minority of patients under oral anticoagulation therapy, a shorter duration of clopidogrel (e.g., 3-month triple therapy with acetylsalicylic acid, clopidogrel, and warfarin) was recommended.
Continuous variables are expressed as mean ± SD and were compared using analysis of variance. Categorical data are presented as frequency (percentage) and were compared using chi-square test. Survival curves were constructed for time-to-event variables using Kaplan–Meier estimates and compared by log-rank test. Patients lost to follow-up were considered at risk until the date of last contact, at which point they were censored. Overall association between BMI and clinical outcome at 5 years was further examined using univariate and multivariate Cox proportional hazard models. In multivariate models, adjustments were made for the potential confounders of age, gender, smoking status, diabetes, hypercholesterolemia, hypertension, lesion length, stent diameter, stent type, clopidogrel duration, and acute coronary syndrome. A colinearity test on explanatory variables included in the models was performed. A p value <0.05 was considered statistically significant and all tests were 2-tailed.
BMI was available in 7,533 of the 8,146 patients enrolled in the Bern–Rotterdam registry, and complete clinical follow-up at 5 years was achieved in 7,427 patients, which represents 98.6% of all patients with an available BMI. Clinical and procedural characteristics of all patients are presented in Table 1 . Forty-five percent of patients (n = 3,404) were overweight, 22% (n = 1,661) were obese, and 33% (n = 2,468) had a normal BMI. Of note, there was a significant trend toward a higher incidence of diabetes, hypertension, and dyslipidemia with increasing BMI; the normal-weight group was older and presented with a higher rate of acute coronary syndromes compared to the overweight and obese groups. Proportions of patients >65 years old in the normal, overweight, and obese BMI groups were 47%, 43%, and 37%, respectively (p = 0.03).
|Variable||BMI <25 kg/m 2||BMI 25–30 kg/m 2||BMI >30 kg/m 2||p Value|
|(n = 2,468)||(n = 3,404)||(n = 1,661)|
|Women||723 (29.3%)||720 (21.2%)||476 (28.7%)||<0.05|
|Mean body mass index (kg/m 2 )||22.83 ± 2.37||27.29 ± 1.38||33.44 ± 5.03||N/A|
|Age (years)||63.52 ± 1.22||62.61 ± 1.12||61.26 ± 1.15||<0.05|
|Acute coronary syndrome||1,376 (56%)||1,770 (52%)||840 (51%)||<0.05|
|Stable angina pectoris||1,084 (44%)||1,623 (48%)||818 (49%)||<0.05|
|Blood pressure ≥165/95 mm Hg||981 (40%)||1,608 (45%)||979 (59%)||<0.05|
|Diabetes mellitus||285 (12%)||523 (15%)||451 (27%)||<0.05|
|Total cholesterol >190 mg/dl||1,130 (46%)||1,820 (53%)||960 (58%)||<0.05|
|Current smoker||907 (37%)||1,260 (38%)||652 (39%)||NS|
|Bifurcation treatment||135 (11%)||191 (12%)||95 (13%)||NS|
|Sirolimus eluting stent||1,316 (53%)||1,735 (51%)||827 (50%)||NS|
|Renal impairment||40 (4.0%)||54 (4.0%)||27 (4.0%)||NS|
|Left ventricular ejection fraction (%)||55 ± 12||55 ± 12||55 ± 11||NS|
|Total stent length (mm) per patient||36 ± 27||36 ± 26||36 ± 25||NS|
|Average stent diameter (mm) per patient||2.92 ± 0.36||2.93 ± 0.37||2.95 ± 0.37||NS|
Unadjusted and adjusted clinical outcomes at 5-year follow-up stratified according to the 3 BMI groups are listed in Table 2 . Kaplan–Meier survival curves for all-cause death; myocardial infarction; clinically justified TVR; composite of all-cause death, myocardial infarction, and clinically justified TVR; and stent thrombosis in the 3 BMI groups at 5-year follow-up are displayed in Figure 1 .
|Censored Events (%)||Unadjusted HR (95% CI)||p Value||Adjusted HR ⁎ (95% CI)||p Value|
|Normal body mass index (reference)||12.6%|
|Overweight||9.8%||0.76 (0.65–0.89)||0.01||0.73 (0.59–0.94)||0.01|
|Obese||9.6%||0.76 (0.63–0.92)||0.05||0.74 (0.53–0.99)||0.05|
|Normal body mass index (reference)||4.9%|
|Overweight||4.9%||0.98 (0.77–1.24)||0.87||0.86 (0.60–1.21)||0.39|
|Obese||5.3%||1.08 (0.82–1.42)||0.57||0.99 (0.65–1.51)||0.97|
|Target vessel revascularization|
|Normal body mass index (reference)||12.8%|
|Overweight||13.7%||1.06 (0.92–1.23)||0.41||0.92 (0.73–1.16)||0.48|
|Obese||15.3%||1.21 (1.02–1.43)||0.02||1.05 (0.79–1.39)||0.73|
|Death/myocardial infarction/target vessel revascularization|
|Normal body mass index (reference)||25.5%|
|Overweight||24.1%||0.93 (0.84–1.04)||0.20||0.84 (0.61–0.98)||0.30|
|Obese||25.2%||1.00 (0.88–1.13)||0.97||0.87 (0.71–1.06)||0.17|
|Definite stent thrombosis|
|Normal body mass index (reference)||3.1%|
|Overweight||2.8%||0.88 (0.65–1.19)||0.41||0.68 (0.43–1.07)||0.10|
|Obese||2.9%||0.93 (0.65–1.34)||0.41||0.78 (0.45–1.35)||0.37|
|Early stent thrombosis (<30 days)|
|Normal body mass index (reference)||0.9%|
|Overweight||1.1%||1.12 (0.66–1.86)||0.67||0.94 (0.43–1.00)||0.05|
|Obese||1.5%||1.47 (0.83–1.70)||0.03||0.56 (0.31–1.03)||0.06|
|Late stent thrombosis (≥30–≤365 days)|
|Normal body mass index (reference)||0.6%|
|Overweight||0.5%||0.76 (0.55–1.53)||0.44||0.53 (0.21–1.35)||0.19|
|Obese||0.4%||0.58 (0.23–1.51)||0.27||0.47 (0.12–1.73)||0.25|
|Very late stent thrombosis (>365 days)|
|Normal body mass index (reference)||1.6%|
|Overweight||1.2%||0.74 (0.47–1.15)||0.18||0.55 (0.27–1.09)||0.09|