2.1

Study population

Between September 2006 and February 2010, 199 consecutive patients with STEMI at the Osaka Minami Medical Center underwent primary PCI within 12 hours after onset of symptoms or up to 48 hours after onset of symptoms if there was evidence of continuing myocardial ischemia. Emergent PCI is available at all times (including weekends) in our facility. Patients meeting the following criteria were eligible for primary PCI: (1) typical chest pain lasting over 30 minutes, and (2) at least 1 mm of new ST-segment elevation in two or more contiguous precordial leads or in two continuous limb leads, or new left bundle branch block on the 12-lead electrocardiogram. Twelve patients (6.4%) were dead during hospitalization [cardiogenic shock ( n = 3), heart failure ( n = 8), pneumonia ( n = 1)]. Of them, 5 patients were excluded from study due to death within 2 days after admission. Thus, 194 patients were available for analysis to predict incidence of CI-AKI, and 187 survivors were available for analysis to assess clinical outcomes between patients with and without CI-AKI. All patients provided written informed consent to participate in this study, which was approved by the Institutional Ethics Committee of Osaka Minami Medical Center and performed in accordance with the principles of the Declaration of Helsinki.

2.2

Data collection and primary PCI

Upon admission to our institution, a 12-lead electrocardiogram was performed, and venous blood samples were obtained before administration of any medications. If primary PCI was indicated, patients were pretreated with aspirin (330 mg), ticlopidine (200 mg) or clopidogrel (150-300 mg) and with intravenous heparin (5000 IU) in the coronary care unit. As soon as written informed consent for invasive treatment was obtained, an urgent coronary angiography was performed with nonionic, low-osmolar (790 mOsm/kg H ₂ O), iodinated contrast agent (Optiray350®, Covidien Japan, Tokyo, Japan). The interventional strategy was left to the discretion of the operators. To reduce the amount of contrast agent, left ventriculography was not performed in any patient.

During the procedure, intravenous heparin was administered to maintain an activated clotting time of 250 to 350 seconds. Post-procedural antithrombotic therapy consisted of aspirin (81 to 100 mg once daily) and ticlopidine (100 mg twice daily) or clopidogrel (75 mg once daily). Procedural success was defined as residual lumen diameter stenosis < 50% with Thrombolysis in Myocardial Infarction (TIMI) grade ≥ 3 flow. Unsuccessful reperfusion was classified as failed angioplasty (residual lumen diameter stenosis > 50% with TIMI grade 0 to 3 flow) and angiographic no-reflow (residual lumen diameter stenosis > 50% with TIMI grade < 2 flow). A detailed medical history, including assessment of classical coronary risk factors, smoking status and others, was obtained after PCI. We used an estimated glomerular filtration rate (eGFR) to evaluate renal function, which was calculated by the new Japanese coefficient-modified Modification of Diet in Renal disease study equation, 194 × serum creatinine (sCr) ^{− 1.094} × age ^{− 0.287} × 0.739 (if female) . Renal insufficiency and contrast-induced acute kidney injury were defined as an eGFR < 60 ml/min per 1.73 m ² on admission and a 50% increase in sCr or an increase in sCr of 0.5 mg/dl from baseline sCr values within 48 hours after primary PCI. Excessive contrast volume used during primary PCI indicates more than the maximum allowable amount of contrast agent, previously described as > 5 × body weight (kg)/sCr (mg/dl) ml (up to 300 ml) in patients with STEMI . Clinical outcomes after discharge were measured in terms of all-cause mortality and cardiovascular events (acute coronary syndrome requiring revascularization, unplanned hospitalization for heart failure and stroke) and were compared between patients with and without CI-AKI. Patients who underwent elective planned PCIs for residual obstructive lesions and in-stent restenosis were excluded from analysis of outcomes. Clinical follow-up data were obtained by either a medical chart review or a phone interview with patients or their referring physicians.

2.3

Statistical analysis

Continuous data are expressed as means ± standard deviation. Categorical variables are expressed as numbers and percentages and were compared by the chi-square test or Fisher’s exact test. Predictors of CI-AKI were assessed by multivariate logistic regression analysis using variables with a P value < .10 on univariate analysis. Receiver-operator characteristics analysis was used to determine the optimal cut-off point for an eGFR on admission to develop CI-AKI. Event-free survival probabilities for mortality and cardiovascular events in patients with vs. without CI-AKI were estimated using the Kaplan–Meier method, and their differences were assessed using a log-rank test. To identify predictors of worse outcomes, stepwise Cox proportional hazards regression analysis was conducted. A P value < .05 was considered statistically significant. All statistical analyses were performed using MedCalc software, version 12.3.0 (Mariakeeke, Belgium).

2.1

Study population

Between September 2006 and February 2010, 199 consecutive patients with STEMI at the Osaka Minami Medical Center underwent primary PCI within 12 hours after onset of symptoms or up to 48 hours after onset of symptoms if there was evidence of continuing myocardial ischemia. Emergent PCI is available at all times (including weekends) in our facility. Patients meeting the following criteria were eligible for primary PCI: (1) typical chest pain lasting over 30 minutes, and (2) at least 1 mm of new ST-segment elevation in two or more contiguous precordial leads or in two continuous limb leads, or new left bundle branch block on the 12-lead electrocardiogram. Twelve patients (6.4%) were dead during hospitalization [cardiogenic shock ( n = 3), heart failure ( n = 8), pneumonia ( n = 1)]. Of them, 5 patients were excluded from study due to death within 2 days after admission. Thus, 194 patients were available for analysis to predict incidence of CI-AKI, and 187 survivors were available for analysis to assess clinical outcomes between patients with and without CI-AKI. All patients provided written informed consent to participate in this study, which was approved by the Institutional Ethics Committee of Osaka Minami Medical Center and performed in accordance with the principles of the Declaration of Helsinki.

2.2

Data collection and primary PCI

Upon admission to our institution, a 12-lead electrocardiogram was performed, and venous blood samples were obtained before administration of any medications. If primary PCI was indicated, patients were pretreated with aspirin (330 mg), ticlopidine (200 mg) or clopidogrel (150-300 mg) and with intravenous heparin (5000 IU) in the coronary care unit. As soon as written informed consent for invasive treatment was obtained, an urgent coronary angiography was performed with nonionic, low-osmolar (790 mOsm/kg H ₂ O), iodinated contrast agent (Optiray350®, Covidien Japan, Tokyo, Japan). The interventional strategy was left to the discretion of the operators. To reduce the amount of contrast agent, left ventriculography was not performed in any patient.

During the procedure, intravenous heparin was administered to maintain an activated clotting time of 250 to 350 seconds. Post-procedural antithrombotic therapy consisted of aspirin (81 to 100 mg once daily) and ticlopidine (100 mg twice daily) or clopidogrel (75 mg once daily). Procedural success was defined as residual lumen diameter stenosis < 50% with Thrombolysis in Myocardial Infarction (TIMI) grade ≥ 3 flow. Unsuccessful reperfusion was classified as failed angioplasty (residual lumen diameter stenosis > 50% with TIMI grade 0 to 3 flow) and angiographic no-reflow (residual lumen diameter stenosis > 50% with TIMI grade < 2 flow). A detailed medical history, including assessment of classical coronary risk factors, smoking status and others, was obtained after PCI. We used an estimated glomerular filtration rate (eGFR) to evaluate renal function, which was calculated by the new Japanese coefficient-modified Modification of Diet in Renal disease study equation, 194 × serum creatinine (sCr) ^{− 1.094} × age ^{− 0.287} × 0.739 (if female) . Renal insufficiency and contrast-induced acute kidney injury were defined as an eGFR < 60 ml/min per 1.73 m ² on admission and a 50% increase in sCr or an increase in sCr of 0.5 mg/dl from baseline sCr values within 48 hours after primary PCI. Excessive contrast volume used during primary PCI indicates more than the maximum allowable amount of contrast agent, previously described as > 5 × body weight (kg)/sCr (mg/dl) ml (up to 300 ml) in patients with STEMI . Clinical outcomes after discharge were measured in terms of all-cause mortality and cardiovascular events (acute coronary syndrome requiring revascularization, unplanned hospitalization for heart failure and stroke) and were compared between patients with and without CI-AKI. Patients who underwent elective planned PCIs for residual obstructive lesions and in-stent restenosis were excluded from analysis of outcomes. Clinical follow-up data were obtained by either a medical chart review or a phone interview with patients or their referring physicians.

2.3

Statistical analysis

Continuous data are expressed as means ± standard deviation. Categorical variables are expressed as numbers and percentages and were compared by the chi-square test or Fisher’s exact test. Predictors of CI-AKI were assessed by multivariate logistic regression analysis using variables with a P value < .10 on univariate analysis. Receiver-operator characteristics analysis was used to determine the optimal cut-off point for an eGFR on admission to develop CI-AKI. Event-free survival probabilities for mortality and cardiovascular events in patients with vs. without CI-AKI were estimated using the Kaplan–Meier method, and their differences were assessed using a log-rank test. To identify predictors of worse outcomes, stepwise Cox proportional hazards regression analysis was conducted. A P value < .05 was considered statistically significant. All statistical analyses were performed using MedCalc software, version 12.3.0 (Mariakeeke, Belgium).