We retrospectively reviewed patients who had received PCI for CAD from 2006 to 2015 at the Taipei Veterans General Hospital. Patients with a measured serum phosphate level at enrollment, who underwent successful PCI, were enrolled. The demographic characteristics, biochemical data, procedural details, and clinical outcomes of these patients were collected from the electronic medical record review. This study followed the Declaration of Helsinki and was approved by the Internal Research Board of Taipei Veterans General Hospital (IRB No. 2016-03-014CC).
It was not appropriate or possible to involve patients or the public in the design, or conduct, or reporting, or dissemination plans of our research. The patient data used in this study was untraceable and anonymous before entering the analysis. According to the Internal Research Board of Taipei Veterans General Hospital, patient informed consent formed was not required.
PCI procedures were performed in conformity with the 2010 ESC/EACTS guidelines on myocardial revascularization. 30 In brief, coronary angiography was performed with standard procedures. Unfractionated heparin was administered to achieve an activated clotting time of > 300 s. After successful wire-crossing, lesion modification was usually performed by balloon dilatations. Rotablations were performed for heavily calcified or balloon-uncrossable lesions. Following dilatation and/or lesion modification, a stent was deployed for most lesions. Successful PCI was defined as residual stenosis < 30% with thrombolysis in MI (TIMI), grade 3 flow at the end of the procedure. Following the procedures, all patients received aspirin (100 mg/d) indefinitely and a P2Y12 inhibitor for at least one month if a bare-metal stent (BMS) was deployed, or at least one year if a drug-eluting stent (DES) was deployed. All patients were observed for a minimum of 8 hours and then discharged under stable conditions.
Baseline information such as body mass index (BMI) and smoking status were collected. We obtained a detailed medical history for comorbid conditions such as hypertension (HTN), diabetes mellites (DM), dyslipidemia, stroke, chronic kidney disease (CKD), heart failure (HF), and the medication history transcribed from electronic medical records. Procedure details of the PCI, including indication for the procedure (ACS or elective), the type of deployed stents (BMSs or DESs), were collected from the procedure notes. Biochemical parameters, including serum phosphate, serum calcium, serum creatinine, uric acid, hemoglobin, low-density lipoprotein-cholesterol (LDL-C), and high-density lipoprotein-cholesterol (HDL-C), were measured using a TBA-c16000 automatic analyzer (Toshiba Medical Systems, Tochigi, Japan) following an overnight fast before the index procedure. The ejection fraction from the left ventriculography and echocardiographic study were also evaluated when available.
The primary endpoint was the composite of CV deaths, nonfatal MIs, nonfatal strokes, or HF hospitalizations. The key secondary outcome was major adverse CV events [MACE, defined as the composite of CV deaths, nonfatal MIs, and nonfatal strokes]. Other secondary outcomes included the individual components of MACE, HF hospitalizations, and repeat revascularization.
The data was expressed as mean ± standard deviation for continuous variables and mean ± 95% confidence interval (CI) for categorical variables. Demographic characteristics and biochemical variables were compared using the Student’s t-test and the Mann–Whitney U test to compare continuous variables when appropriate, with chi-square tests used for categorical variables. The association between the serum phosphate level and clinical and biochemical variables was evaluated sequentially with multiple linear regression. To evaluate the association between serum phosphate and clinical outcomes, the serum phosphate was categorized into four quartiles. Survival to the primary and secondary endpoints of the four groups was compared with the stepwise Cox proportional hazards models, while backward selection was used to calculate hazard ratios (HRs) and 95% CI for serum phosphate categories. To adjust for confounding variables, a second Cox hazard ratio was performed with adjustment for age, gender, hypertension, DM, smoking status, and estimated glomerular filtration rate (eGFR). Subgroup and sensitivity analyses were also performed. Prespecified subgroups in these analyses were defined according to age (< 65 years of age, or > 65 years of age or older), gender, DM, hypertension (HTN), smoking, BMI (< 22kg/m2, or 22kg/m2 or more), LDL (< 70 mg/dL, 70 mg/dL or more), HDL (< 40 mg/dL, 40 mg/dL or more), ACS, eGFR (< 60 ml/min/1.732, 60 ml/min/1.732 or more), LVEF (< 50%, 50% or more), DES use, and dialysis status. Statistical significance was set as P < 0.05. All statistical analyses were carried out with SPSS 20.0 software (IBM, Inc. Chicago, IL, USA)