Limited information is available regarding the impact of acute kidney injury (AKI) during hospitalization on clinical outcomes after myocardial infarction (MI), and the effect of transient kidney injury (KI) on long-term mortality has not been validated. We retrospectively analyzed 2,289 patients diagnosed with MI. AKI patients were classified into a transient KI group and a persistent KI group based on serum creatinine levels at discharge. The end point of the study was 3-year mortality after MI. We included 2,110 patients of whom 237 patients (11%) developed AKI during hospitalization. Of these 237 patients, 154 (65%) had transient KI, and 83 (35%) had persistent KI. Multivariate analysis showed that age, left ventricular ejection fraction, estimated glomerular filtration rate on admission, and Killip class were significantly associated with developing AKI during hospitalization. The adjusted hazard ratios for 3-year mortality were 1.71 (95% confidence interval: 1.08–2.70) for AKI patients with transient KI and 2.21 (95% confidence interval: 1.34–3.64) for AKI patients with persistent KI, compared with no AKI. In conclusion, AKI was associated with an increased risk of death for patients who experienced MIs and survived during hospitalization. Although renal function had completely recovered in many AKI patients at discharge, these transient KI patients are also at a great risk of death after MI.
Limited information is available about the effect of acute kidney injury (AKI) during hospitalization on clinical outcomes after myocardial infarction (MI). Furthermore, most of the previous studies did not use a standardized definition of AKI and did not focus on the effect of transient (normalization of serum creatinine [SCr] levels at discharge) and persistent (elevation of SCr levels persist at discharge) kidney injury (KI) on clinical outcomes. Because SCr levels return to normal in some patients after AKI regardless of AKI severity, validating the impact of transient KI on long-term mortality after MI is extremely important. However, it remains unclear whether AKI in which the SCr level completely returns to normal is still associated with an increased risk of death in patients with MI. Therefore, we evaluated the incidence and the prognostic impact of transient and persistent AKI in patients with MI.
Methods
Between January 2006 and October 2009, 2,289 patients were diagnosed with MI and admitted to the emergency department of Chonnam National University Hospital; they were evaluated retrospectively. Of the 2,289 patients, 111 who died during hospitalization excluded from the study, and an additional 68 patients were excluded because they met the following exclusion criteria: lack of at least 2 SCr measurements during hospitalization, lack of follow-up data after discharge, end-stage renal disease with dialysis, and admission SCr level ≥4.0 mg/dl. The patients’ demographic, clinical, laboratory, and treatment data were obtained from the hospital’s computerized database. Hypertension was defined as systolic blood pressure >140 mm Hg and/or diastolic blood pressure >90 mm Hg at rest at repeated measurements or treatment with antihypertensive medications. Hyperlipidemia was defined as treatment with a lipid-lowering agent. MI was diagnosed on the basis of the triad of chest pain, electrocardiogram (ECG) changes, and raised serum cardiac enzyme level. In the MI patients, ST-segment elevated MI (STEMI) was defined by the presence of new ST-segment elevation of at least 1 mm (0.1 mV) in continuous leads or new left bundle-branch block on the index or electrocardiogram, and those who were not classified as STEMI were considered to have non-STEMI (NSTEMI) given the presence of positive biomarkers in all patients. The primary end point of the study was 3-year mortality after MI. Assessment of the survival status and validation of clinical outcomes were performed by collecting records from the outpatients clinic or by follow-up telephone interviews. This study was approved by the institutional review board of Chonnam National University Hospital, Gwangju, Republic of Korea.
AKI was defined, according to the recently proposed standard Kidney Disease: Improving Global Outcomes (KDIGO) guidelines, as an absolute increase in the SCr level to ≥0.3 mg/dl within 48 hours or an increase in the SCr level to ≥1.5 times the baseline value, which is known or presumed to have occurred within the previous 7 days. Urine output was not considered a criterion for AKI in this study. Serial SCr levels during hospitalization were obtained from the patients’ medical records and reviewed by a trained study coordinator. The patients who met the AKI criteria were further classified into a transient KI group (normalization of SCr level at discharge; SCr level ≤1.3 mg/dl) and a persistent KI group (sustained elevation of SCr level at discharge; SCr level >1.3 mg/dl). On admission, initial renal function was assessed as the estimated glomerular filtration rate (eGFR), which was calculated using the CKD-Epidemiology Collaboration equation.
Continuous variables have been provided as either mean (±SD) or median (with 25th and 75th percentiles) values, and categorical variables have been provided as numbers and percentages. Baseline characteristics between the groups were compared using 1-way analysis of variance or Student t test for continuous variables and by Pearson chi-squared test or Fisher exact for categorical variables. Logistic regression analysis was performed to determine the independent predictors of AKI. The variables analyzed included age, gender, body mass index (BMI; ≥25 kg/m 2 ), comorbidities (hypertension, diabetes mellitus, ischemic heart disease, hyperlipidemia, smoking status), left ventricle ejection fraction (LVEF), Killip class, diagnosis (STEMI vs NSTEMI), eGFR on admission, coronary angiography and coronary artery bypass graft during hospitalization, and medical treatments during hospitalization. The 3-year mortality was estimated by the Kaplan-Meier method, and curves were compared with the log-rank test. Univariate and multivariate Cox proportional regression analyses were performed to assess the relationship between AKI and 3-year mortality. The following baseline characteristics were considered in the multivariate analysis: age, gender, BMI (≥25 kg/m 2 ), comorbidities (hypertension, diabetes mellitus, ischemic heart disease, hyperlipidemia, and smoking status), Killip class, LVEF, diagnosis (STEMI vs NSTEMI), eGFR on admission, coronary angiography and coronary artery bypass graft during hospitalization, and medical treatments during hospitalization. Age, LVEF, and eGFR on admission analyzed as continuous variables. All statistical tests were 2-tailed, and p <0.05 was considered significant. Statistical analysis was performed using the Statistical Package for Social Sciences software, version 18.0 (SPSS, IBM, Armonk, New York).
Results
The present study included 2,110 patients (mean age, 63.1 ± 12.7 years; men, 71%). Of these patients, 237 patients (11%) developed AKI during hospitalization; 154 (65%) had transient KI and 83 (35%) had persistent KI. The baseline characteristics, clinical presentations on admission, and in-hospital treatments of the patients in all the groups are shown in Tables 1 and 2 . Multivariate logistic regression analysis was used to identify significant predictors of AKI during hospitalization. Multivariate analysis showed that age, eGFR on admission, Killip classes, coronary bypass graft during hospitalization, and medication aldosterone receptor antagonist were significantly associated with developing AKI during hospitalization after multivariate adjustment ( Table 3 ).
| Variable | Total (n = 2,110) | No AKI (n = 1,866) | AKI With Transient KI (n = 154) | AKI With Persistent KI (n = 83) | p Value ∗ | p Value † |
|---|---|---|---|---|---|---|
| Age (yrs) | 63.1 ± 12.7 | 62.3 ± 12.7 | 67.9 ± 11.7 | 72.9 ± 9.9 | <0.001 | 0.001 |
| Male (%) | 1,508 (71%) | 1,363 (72%) | 88 (57%) | 57 (68%) | <0.001 | 0.082 |
| BMI (kg/m 2 ) | 24.1 ± 3.1 | 24.2 ± 3.1 | 23.7 ± 3.5 | 23.1 ± 2.8 | 0.004 | 0.260 |
| Hypertension | 980 (46%) | 840 (44%) | 81 (52%) | 59 (71%) | <0.001 | 0.006 |
| Diabetes mellitus | 552 (26%) | 465 (24%) | 52 (33%) | 35 (42%) | <0.001 | 0.200 |
| Ischemic heart disease | 283 (13%) | 242 (12%) | 24 (15%) | 17 (20%) | 0.034 | 0.342 |
| Hyperlipidemia | 92 (4.4%) | 86 (4.6%) | 3 (1.9%) | 3 (3.6%) | 0.246 | 0.436 |
| Smoker | 1,301 (61%) | 1,179 (62%) | 78 (50%) | 44 (53%) | 0.002 | 0.728 |
| Admission SCr (mg/dl) | 0.99 ± 0.37 | 0.95 ± 0.32 | 0.98 ± 0.35 | 1.70 ± 0.64 | <0.001 | <0.001 |
| Admission eGFR rate (ml/min/1.73 m 2 ) | 80.0 ± 22.6 | 82.1 ± 21.1 | 74.3 ± 24.1 | 42.3 ± 17.7 | 0.019 | <0.001 |
| Admission eGFR rate <60 (ml/min/1.73 m 2 ) | 407 (19%) | 289 (15%) | 48 (31%) | 70 (84%) | <0.001 | <0.001 |
| Peak SCr (mg/dl) | 1.11 ± 0.60 | 1.00 ± 0.35 | 1.44 ± 0.58 | 2.88 ± 1.51 | <0.001 | <0.001 |
| Discharge SCr (mg/dl) | 0.93 ± 0.63 | 0.86 ± 0.29 | 0.95 ± 0.22 | 2.34 ± 2.44 | <0.001 | <0.001 |
∗ Comparison among patients without AKI, AKI patients with transient KI, and AKI patients with persistent KI.
† Comparison between AKI patients with transient KI and AKI patients with persistent KI.
| Variable | Total (n = 2,110) | No AKI (n = 1,866) | AKI With Transient KI (n = 154) | AKI With Persistent KI (n = 83) | p Value ∗ | p Value † |
|---|---|---|---|---|---|---|
| Initial presentation | ||||||
| Systolic BP (mm Hg) | 131 ± 28 | 131 ± 27 | 127 ± 41 | 126 ± 34 | 0.081 | 0.878 |
| Diastolic BP (mm Hg) | 81 ± 17 | 82 ± 16 | 78 ± 25 | 79 ± 21 | 0.028 | 0.686 |
| Heart rate (beats/min) | 76 ± 18 | 75 ± 17 | 77 ± 27 | 80 ± 22 | 0.031 | 0.466 |
| LVEF (%) | 55.2 ± 12.3 | 56.0 ± 12.0 | 51.3 ± 13.5 | 45.6 ± 12.4 | <0.001 | 0.002 |
| Killip class | <0.001 | 0.020 | ||||
| I | 1,647 (78%) | 1,537 (82%) | 80 (51%) | 30 (36%) | ||
| II | 211 (10%) | 169 (9%) | 26 (16%) | 16 (19%) | ||
| III | 173 (8%) | 116 (6%) | 28 (18%) | 29 (34%) | ||
| IV | 79 (3%) | 51 (2%) | 20 (13%) | 8 (9%) | ||
| Diagnosis | ||||||
| STEMI | 1,217 (57%) | 1,072 (57%) | 103 (66%) | 42 (50%) | 0.814 | 0.014 |
| NSTEMI | 893 (42%) | 801 (42%) | 51 (33%) | 41 (49%) | 0.814 | 0.014 |
| Duration of hospital stay (days) | 10.1 ± 9.8 | 9.1 ± 7.9 | 16.9 ± 15.2 | 21.2 ± 20.3 | <0.001 | 0.097 |
| In-hospital treatment | ||||||
| CA | 1,780 (84%) | 1,587 (86%) | 127 (84%) | 66 (80%) | 0.108 | 0.416 |
| CABG | 43 (2.0%) | 31 (1.7%) | 8 (5.2%) | 4 (4.8%) | 0.001 | 0.584 |
| Medication | ||||||
| Aspirin | 2,091 (99%) | 1,857 (99%) | 152 (98%) | 82 (98%) | 0.510 | 0.719 |
| Clopidogrel | 2,072 (98%) | 1,839 (98%) | 151 (98%) | 82 (98%) | 0.823 | 0.562 |
| Beta blocker | 1,797 (85%) | 1,598 (85%) | 129 (83%) | 70 (84%) | 0.622 | 0.909 |
| ACE inhibitor or ARB | 1,883 (89%) | 1,686 (90%) | 126 (81%) | 71 (85%) | 0.003 | 0.465 |
| ARA | 316 (15%) | 224 (12%) | 55 (35%) | 37 (44%) | <0.001 | 0.182 |
| Statin | 1,508 (71%) | 1,347 (72%) | 104 (67%) | 57 (68%) | 0.426 | 0.857 |
∗ Comparison among patients without AKI, AKI patients with transient KI, and AKI patients with persistent KI.
† Comparison between AKI patients with transient KI and AKI patients with persistent KI.
| Predictor | OR | 95% CI | p Value |
|---|---|---|---|
| Age per yr increase | 1.02 | 1.01–1.04 | 0.005 |
| Admission eGFR per ml/min/1.73 m 2 increase | 0.98 | 0.97–0.99 | <0.001 |
| Killip class | |||
| Killip class I | 1 (ref) | ||
| Killip class II | 2.37 | 1.54–3.65 | <0.001 |
| Killip class III | 2.28 | 1.42–3.66 | 0.001 |
| Killip class IV | 3.40 | 1.81–6.36 | <0.001 |
| CABG during hospitalization | 2.70 | 1.08–6.72 | 0.033 |
| LVEF per % increase | 0.99 | 0.98–1.00 | 0.085 |
| Female | 0.92 | 1.01–1.04 | 0.701 |
| BMI (≥25 kg/m 2 ) | 1.06 | 0.75–1.49 | 0.732 |
| Comorbidities | |||
| Hypertension | 1.16 | 0.84–1.62 | 0.369 |
| Previous ischemic heart disease | 1.23 | 0.80–1.89 | 0.352 |
| Diabetes mellitus | 1.25 | 0.89–1.76 | 0.206 |
| Hyperlipidemia | 0.64 | 0.25–1.63 | 0.350 |
| Smoking | 1.04 | 0.68–1.57 | 0.873 |
| STEMI | 1.26 | 0.89–1.78 | 0.189 |
| Performed coronary angiography | 1.10 | 0.62–1.92 | 0.756 |
| In-hospital medication | |||
| Aspirin | 0.44 | 0.06–3.48 | 0.436 |
| Clopidogrel | 0.96 | 0.21–4.32 | 0.956 |
| Beta blocker | 1.36 | 0.82–2.25 | 0.231 |
| ACE inhibitor or ARB | 0.56 | 0.33–0.94 | 0.029 |
| ARA | 2.33 | 1.61–3.37 | <0.001 |
| Statin | 1.07 | 0.75–1.54 | 0.697 |
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