A retrospective study was performed for 149 patients, including 37 (24.9%) female patients, with AMI who successfully received PCI with or without coronary stenting between February 2013 and December 2014 at Chonnam National University Hospital, Gwangju, Korea. Patients were followed up by visits to the outpatient department or via telephone contact. Data on clinical characteristics, laboratory characteristics, and procedural findings for patients with and without MACE were obtained through a retrospective review of clinical records. The median follow-up duration was 30.1 months (interquartile range [IQR], 22.9–36.8 months). The median age was 67 years. Complete blood counts (CBC), glucose, creatinine, and high-sensitivity C-reactive protein (hsCRP) levels were measured at the time of admission. Lipid profiles were obtained after at least 9 hours of fasting within 24 hours of hospitalization. All parameters were measured using an automated chemistry analyzer (AU5832, Beckman Coulter Inc., Brea, CA, USA), except for CBC, which were analyzed using the XE-2100 system (Sysmex Corp., Kobe, Japan). Patients received a loading dose of 300 mg aspirin and other antiplatelet medication (600 mg clopidogrel, 60 mg prasugrel, or 180 mg ticagrelor) prior to PCI. Unfractionated heparin (50–70 U/kg) was administered prior to or during PCI to maintain an activated clotting time of 250–300 seconds. After PCI, 100–300 mg aspirin and 75 mg clopidogrel (10 mg prasugrel or 180 mg ticagrelor) were prescribed daily as a maintenance dose. This study was conducted in accordance with the Declaration of Helsinki and approved by the ethics committee of Chonnam National University Hospital, Gwangju, Korea. We used serum samples that were already collected in another prospective registry of our institution (IRB number: CNUH-2016-048). The requirement for informed consent was waived because of the retrospective nature of the current study.

Blood samples were obtained from 149 patients immediately after successful PCI and collected in serum-separating tubes (Becton Dickinson, Franklin Lakes, NJ, USA). All samples were immediately centrifuged at 2,465 g for 10 minutes at room temperature (20–25℃) and processed according to a standardized operating procedure [13]. Serum samples were stored at −80℃ until analyzed. Copeptin levels were measured using a time-resolved amplified cryptate emission immunoassay (Thermo Fisher Scientific Clinical Diagnostics BRAHMS GmbH, Hennigsdorf, Germany). This assay had a limit of detection of 0.9 pmol/L and a functional sensitivity of 1.9 pmol/L, assessed as an inter-assay precision of 20%. Intra- and inter-assay precision was 2.9% and 2.4%, respectively, at low-level quality control and 2% and 2.2%, respectively, at high-level quality control. The measuring range with automatic dilution was 1.9–2,000 pmol/L.

For reference interval verification of serum copeptin levels, 206 healthy controls (109 males and 97 females) aged 35–87 years were selected among the people who visited the Health Promotion Center; these controls had normal routine laboratory parameters such as renal and liver function tests.

ST-segment elevation MI (STEMI) and non-STEMI (NSTEMI) diagnoses were based on the third universal definition of MI [14]; diagnoses were made by at least two interventional cardiologists at our institution. STEMI diagnosis was also based on recent guidelines for the management of STEMI, with a 12-lead electrocardiogram evaluating infarct-related arteries as determined by coronary angiography with increased cardiac-specific biomarkers such as troponin-I (TnI) [15]. Baseline left ventricular ejection fraction was measured by two-dimensional echocardiography prior to or immediately after PCI. The extent of coronary blood flow prior to and post PCI was graded using thrombolysis in MI (TIMI) flow grade. Complexity of coronary lesions was based on the definitions of the American College of Cardiology/American Heart Association [1617]. Multivessel disease was defined as coronary lesions associated with 50% or more stenosis in at least two coronary arteries, including the culprit artery, by quantitative coronary analysis. The culprit vessel was determined by 12-lead electrocardiogram and coronary angiography in STEMI. For NSTEMI, the culprit vessel was determined by coronary angiography. Coronary stenting was performed for individual patients at the discretion of the operators.

The study endpoint was MACE, a term that comprises all-cause death, any repeat PCI, recurrent MI, and coronary artery bypass graft. Nonfatal recurrent MI was defined as the development of recurrent angina symptoms accompanied by changes in 12-lead electrocardiogram or increased levels of cardiac-specific biomarkers. Repeat PCI included target lesion revascularization, target vessel revascularization, and non-target vessel revascularization [18].

Continuous variables were presented as mean±SD or as median with interquartile range (IQR). These were compared using the unpaired t-test or Mann-Whitney rank-sum test. Discrete variables were expressed as counts with percentages and were analyzed using Pearson's chi-squared test or Fisher's exact test. As copeptin levels exhibited a right-skewed distribution, data were subjected to a natural log transformation for statistical analysis. Multivariate logistic regression analysis was used to estimate predictors of MACE occurrence. The following variables with P<0.05 in univariate logistic regression were included in multivariate analysis: age, sex, diabetes mellitus, body mass index, previous history of PCI, use of beta-blocker at discharge, log-transformed copeptin (lnCopeptin), white blood cell counts, hemoglobin, low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), and hsCRP. All patients were divided equally into three groups according to copeptin levels. Kaplan-Meier curves were constructed to illustrate MACE incidence over time according to copeptin level tertiles. Differences were assessed with a log-rank test.

All analyses were two-tailed and performed using SPSS for Windows ver. 23.0 (SPSS Inc., Chicago, IL, USA). P<0.05 was considered statistically significant.

Patients' demographic and clinical characteristics are presented in Table 1. Age was significantly higher in MACE patients (N= 34) than in non-MACE patients (N=115), and a higher percentage of MACE patients had type 2 diabetes mellitus and a history of PCI. However, body mass index was higher in non-MACE patients than in MACE patients. In addition, fewer MACE patients than non-MACE patients received beta-blockers as a discharge medication. However, there were no significant differences in atherosclerotic risk factors such as hypertension, smoking, or dyslipidemia. Further, there were no significant differences in the prevalence of multivessel disease, distribution of culprit vessels, lesion complexity, procedural success rate, mean implanted stent number, or coronary stent implantation between MACE and non-MACE patients.

The laboratory characteristics of all 149 patients are presented in Table 2. MACE patients had higher serum copeptin levels (P=0.020), hsCRP (P=0.019), serum glucose levels (P=0.007), and WBC count (P=0.013) and lower serum LDL-C levels (P=0.002) and hemoglobin (P=0.007) than non-MACE patients. lnCopeptin was also higher (P=0.011) in MACE patients than in non-MACE patients. Peak levels of cardiac enzyme (TnI and CK-MB) and serum creatinine were similar in both groups.

The median copeptin level of all 206 healthy controls was 2.9 pmol/L. The 97.5th percentile copeptin level of the healthy control group was 9.6 pmol/L, and the 2.5th percentile was 0.9 pmol/L. The median copeptin level was higher in men than in women (men, 3.4 pmol/L; women, 2.3 pmol/L). The median copeptin level in the patient group was higher than in the healthy control group (11.5 pmol/L vs 2.9 pmol/L). Patients with STEMI had higher copeptin levels than NSTEMI patients (65.6 pmol/L vs 10.0 pmol/L; Fig. 1).

Overall, 34 (22.8%) patients experienced MACE during a median follow-up period of 30.1 months (IQR, 22.9–36.8 months). Multiple logistic regression analysis demonstrated that an approximate 2.72-fold increase in copeptin levels was associated with increased MACE (odds ratio, 1.6; 95% confidence interval, 1.15–2.20; P=0.005) after adjusting the following confounders: age, sex, diabetes mellitus, body mass index, previous history of PCI, use of beta-blocker at discharge, lnCopeptin, white blood cell counts, hemoglobin, LDL-C, HDL-C, and hsCRP (Table 3).

The MACE occurrence among the patients in copeptin level tertiles is shown in Fig. 2. There was a statistically significant separation among the estimated Kaplan-Meier survival curves of the copeptin tertiles (P=0.045, log-rank test). Serum copeptin levels were associated with MACE in a dose-dependent manner.