Methods

Since 2009, a prospective PCI Registry has been operated by the Department of Cardiology, Hanyang University Hospital, Seoul, South Korea, to evaluate the clinical outcomes and safety of PCI. Written informed consent was provided by all patients before they were enrolled in the study, and the Hanyang University Hospital Institutional Review Board approved the study protocol. From January 2009 to December 2013, patients who successfully underwent PCI in the Hanyang University Hospital using EESs (Promus Element; Boston Scientific, Marlborough, Massachusetts; and Xience V and Xience Prime; Abbott, Santa Clara, California) to treat at least 1 coronary artery stenosis or occlusion were consecutively enrolled in this study. Patients who had previously undergone PCI or coronary artery bypass surgery for culprit arteries were excluded. Patients who displayed debilitating conditions including advanced malignancies, advanced cirrhosis, end-stage renal disease, severe autoimmune diseases, and cerebrovascular accidents with major sequels were also excluded. Demographic characteristics and medical and social histories were obtained. Body weight, height, and waist circumference (WC) were determined during the periprocedural period (within 7 days). Blood samples for lipid profiles, glucose levels, and serum creatinine levels were obtained from all patients after an 8-hour fasting, in the morning before or after the index PCI. The estimated glomerular filtration rate (eGFR) was calculated using the Modification of Diet in Renal Diseases study equation. Before the procedure, 300 mg of aspirin and P2Y12 inhibitors (600 mg of clopidogrel, 60 mg of prasugrel, or 180 mg of ticagrelor) were administered to all patients. After the index procedure, all patients received dual antiplatelet agent therapy (aspirin 300 mg/day for 1 month followed by 100 mg/day indefinitely and a P2Y12 inhibitor for at least 1 year). All patients received high-dose statin therapy following the index procedure, regardless of their low-density lipoprotein cholesterol (LDL-C) serum levels, unless there were contraindications for statin use.

The recommendations of the Third Report of the National Cholesterol Education Program Expert Panel on the Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) were used to identify the MetS components. WC of ≥90 cm in men and ≥85 cm in women were used as the cut-off values for abdominal obesity (AO), in accordance with the recommendations of the Korean Society for the Study of Obesity. Patients who were regularly taking medications for hypertension or diabetes mellitus (DM) were considered to have the components of MetS, although their blood pressure or fasting glucose levels were lower than the levels in the recommendations. Patients with ≥3 of the earlier mentioned features were diagnosed with MetS.

PCI was performed using standard techniques. To specify the grade of stenosis as a percentage, we compared each stenotic lesion with the lumen of a normal vessel, both proximal and distal to the stenotic area. A coronary artery narrowed that required PCI was defined as an artery with at least 1 luminal narrowing ≥70% based on quantitative angiographic measurements. During the observation period, repeat coronary angiography was performed when patients presented with symptoms of angina or signs of myocardial ischemia. Standardized definitions of clinical events frequently used in cardiovascular trials were used as described by Hicks et al. To blind the status of MetS, a researcher who had not participated in the registry data input collected outcome data, using electrical medical records. Telephone surveys were made for patients who had missed their visits. The first clinical event that occurred after index PCI was used as the clinical event of a patient. Cardiac death included death resulting from acute myocardial infarction (MI), heart failure, or cardiogenic shock. MI was defined as an increase and decrease of cardiac troponin I levels at least 3 times more than the upper normal limit with at least 1 clinical evidence consistent with myocardial ischemia, including symptoms associated with angina, ST-segment changes in electrocardiography, and wall motion abnormalities in echocardiography. Repeat revascularization was defined as balloon angioplasty in the target lesion or repeated stent implantation in the target vessel during the observation period. The repeat revascularization was performed when a luminal narrowing ≥70% was present in the target vessel or functional ischemia in any diagnostic test was present in the target vessel territory. A composite event was defined as the combination of repeat revascularization, nonfatal MI, and cardiac death. PCI for de novo coronary lesions was not considered as revascularization.

The patients were divided into MetS and non-MetS groups. The Student’s t tests were used to compare continuous variables, and the chi-square tests were used to compare categorical variables between the 2 groups. Mann-Whitney tests were used for variables with skewed distributions. A Kaplan-Meier survival analysis was used to compare the event-free survival rates of clinical events between the 2 groups. A univariable Cox regression analysis was performed with all variables to estimate their predictive powers for the composite event. A multivariable Cox regression analysis, including MetS, conventional risk factors of coronary artery disease (CAD), and significant predictors in the univariable analysis as covariates, was performed using a backward selection method. If variables presented collinearity, the variable with the lowest p value in the univariable analysis was included in the multivariable models to avoid multicollinearity problems. To retain marginally significant predictors, the p value for the backward variable selection process was set to ≥0.1. The hazard ratios (HRs) corresponding to the number of coronary arteries narrowed (nCAN) and total stent length (TSL) were simulated to determine graphically, whether the effect of MetS on the composite event changed with the severity of CAD or the extent of PCI. The interaction of nCAN and TSL with the effect of MetS on the risk of the composite event was tested using a Cox regression analysis. All statistical analyses were performed using R 3.0.3 and the survival, forestplot, KMsurv, simPH, and rms packages of the software. A p <0.05 was considered significant.

Results

Of the patients who underwent coronary angiography, 903 patients who had undergone coronary stent implantation with EESs were included. The mean age was 64.8 ± 10.7 years, and 607 patients (67.2%) were men. DM and hypertension were present in 318 (35.2%) and 550 patients (60.9%), respectively. MI and MetS were diagnosed in 157 (17.4%) and 570 patients (63.1%), respectively. Statins were prescribed in 87.4% of the patients after the index PCI. The baseline characteristics are described in Table 1 . SBP, DBP, WC, body mass index (BMI), triglyceride levels, fasting glucose levels, and the prevalence of hypertension and DM were higher, and high-density lipoprotein cholesterol levels, eGFR, and male frequency were lower in the MetS group than in the non-MetS group. The prescribed medications did not differ between the 2 groups, 1 month after the index PCI, except calcium channel blockers that were more frequently prescribed in the MetS group, most likely because the prevalence of hypertension was higher in the MetS group. The duration of dual antiplatelet therapy did not differ between the 2 groups. The patients in the MetS group presented more severe CAD and underwent more extensive PCIs than those in the non-MetS group. Multivessel CAD was more frequent in the MetS group than in the non-MetS group. TSL was longer, the number of implanted stents was greater, and the average stent diameter was smaller in the MetS group than in the non-MetS group. However, overall frequencies of repeat revascularization, nonfatal MI, cardiac death, and the composite event were not different between the 2 groups ( Table 2 ). Kaplan-Meier survival analyses showed that there were also no differences in the event-free survival of repeat revascularization, nonfatal MI, cardiac death, and the composite event between the 2 groups ( Figure 1 ).

Kaplan-Meier survival analyses for the clinical events. There were no significant differences in the event-free survival rates of the clinical events between the MetS and non-MetS groups. “*,” Repeat revascularization + nonfatal MI + cardiac death.

Univariable Cox regression analyses revealed that TSL, nCAN, DM, and eGFR <60 ml/min/m ² were associated with increased risk of the composite event. WC and BMI were not associated with the composite event. However, AO based on WC was associated with decreased risk of the composite event. Because, BMI highly correlated with WC (r = 0.72, p <0.001), we transformed BMI into a dichotomized variable, using gender-specific cut-off points (BMI <24.5 kg/m ² for men and <22.0 kg/m ² in women for “low BMI”) derived from a survival receiver operating characteristic curve analysis for the composite event. Then, low BMI was significantly associated with increased risk of the composite event. Male gender was marginally associated with increased risk of the composite event. Age, hypertension, systolic blood pressure, MI, ST-segment elevation MI, current smoking, LDL-C levels, the types of medications after index PCI, average stent diameter, and MetS components other than AO were not associated with the composite event ( Figure 2 ). Because nCAN and TSL were associated with the composite event, we simulated and plotted the HRs, corresponding to each value of nCAN and TSL in the non-MetS group and the MetS group, respectively. The simulation showed that there were no differences in the HRs of the composite event between the 2 groups, regardless of nCAN and TSL ( Figure 3 ).

Univariate Cox regression analyses for predictors of the composite event. Diabetes, low BMI, TSL, the number of CAS, and eGFR <60 ml/min/1.73 m ² increased composite event occurrence, whereas AO decreased composite event occurrence. The gray bars indicate 95% CIs. “*,” BMI <24.5 kg/m ² for men and <22.0 kg/m ² for women. “**,” Waist circumference ≥90 cm for men and ≥85 cm for women. “†,” Each predictor is a component of MetS.

The influence of MetS on the relation of nCAN and TSL to HRs for the composite event. The presence of MetS has no significant impact on the HRs for the composite events, regardless of nCAN and TSL. The colored lines indicate the simulated HR for the composite event and colored bars indicate the 95% CIs of the HRs at the corresponding x axis value.

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