Very few studies evaluated the impact of acute kidney injury (AKI) and chronic kidney disease (CKD) on heart failure (HF) hospitalization risk following an acute myocardial infarction (AMI ). For this retrospective cohort analysis, we identified adult AMI survivors from January to June 2014 from the United States Nationwide Readmissions Database. Outcomes were a 6-month HF, fatal HF, composite of HF during the AMI or a 6-month HF, and a composite of 6-month HF or death during a non–HF-related admission. We analyzed differences in outcomes across categories of patients without renal injury, AKI without CKD, stable CKD, AKI on CKD, and end-stage renal disease (ESRD). Of 237,549 AMI survivors, AKI was present in 13.8%, CKD in 16.5%, ESRD in 3.4%, and AKI on CKD in 7.7%. Patients with renal failure had lower coronary revascularization rates and higher in-hospital HF. A 6-month HF hospitalization occurred in 12,934 patients (5.4%). Compared with patients without renal failure (3.3%), 6-month HF admission rate was higher in patients with AKI on CKD (14.6%; odds ratio [OR] 1.99; 95% confidence interval [CI] 1.81 to 2.19), ESRD (11.2%; OR 1.57; 95% CI 1.36 to 1.81), stable CKD (10.7%; OR 1.72; 95% CI 1.56 to 1.88), and AKI (8.6%; OR 1.52; 95% CI 1.36 to 1.70). Results were generally homogenous in prespecified subgroups and for the other outcomes. In conclusion, 1 in 4 AMI survivors had either acute or chronic renal failure. The presence of any form of renal failure was associated with a substantially increased risk of 6-month HF hospitalizations and associated mortality with the highest risk associated with AKI on CKD.
Acute kidney injury (AKI) and chronic kidney disease (CKD) are poor prognostic indicators in patients with acute myocardial infarction (AMI). Heart failure (HF), frequently complicates AMI, and the presence of peri-MI or HF after discharge is associated with increased morbidity and mortality. Post-AMI HF is typically diagnosed within the first 6 months after discharge, and HF requiring hospitalization is associated with a worse prognosis compared with HF managed in the outpatient setting. , Whereas several studies have evaluated the long-term risk of HF and related hospitalizations associated with AKI and CKD in a non-AMI setting, very few studied the impact of AKI and CKD on HF hospitalizations following an AMI. , , , Therefore, the purpose of this study was to evaluate the impact of AKI and CKD on the risk for HF hospitalizations in a large sample of AMI survivors from a more contemporary national database. We also studied the influence of underlying baseline CKD on the effect of AKI on HF hospitalizations.
For this retrospective observational study, data were collected from the publicly available 2014 United States Nationwide Readmissions Database (NRD). The NRD is part of the Healthcare Cost and Utilization Project and is a database of all-payer hospital inpatient stays and can be used to generate national estimates of readmissions. The NRD is drawn from state inpatient databases, which contain verified patient linkage numbers that can be used to track a person across readmissions and maintain confidentiality. Unweighted, the 2014 NRD contains data from approximately 15 million discharges from 22 geographically dispersed states accounting for 51.2% of the total United States resident population and 49.3% of all hospitalizations. Weighted, it estimates roughly 35 million discharges. The NRD 2014 was used because it is the latest yearly dataset that allows International Classification of Diseases, Ninth Edition, Clinical Modification (ICD-9-CM) based analysis which was previously validated to study HF outcomes.
The study sample included all patients ≥18 years who were discharged alive, between January and June 2014 with a primary discharge diagnosis of an AMI (ICD-9 Codes 410 × 1). This population and period were chosen so that study patients could be tracked until the end of 2014, thereby allowing for the analysis of 6-month HF hospitalization. Patients with cardiogenic shock were excluded as they represent a complex phenotype associated with heightened acute and mortality after discharge.
Baseline patient characteristics identified were age, gender, insurance status, median household income, AMI type, and comorbidities including anemia, connective tissue disease, carotid artery disease, previous MI, previous coronary revascularization, previous ischemic cerebrovascular event, atrial fibrillation, coronary artery disease, cancer, chronic lung disease, smoking, depression, drug abuse, diabetes mellitus, hypertension, hypothyroidism, fluid-electrolyte imbalances, liver disease, obesity, peripheral vascular disease, pulmonary circulation disorders, CKD Stage III to V, ESRD (ICD-9 585.6), HF during the index admission, discharge disposition, in-hospital outcomes including percutaneous coronary intervention (PCI), coronary artery bypass grafting, any mechanical revascularization, and development of AKI (ICD-9 584.x).
We further classified AKI into AKI without underlying CKD Stage III to V (ICD-9 585.3, 585.4, 585.5, 585.9) and AKI on CKD Stages III to V. CKD was classified into stable CKD (without the development of AKI), and AKI on CKD. Hospital characteristics (bed size and teaching status) were also identified. Elixhauser comorbidity data were extracted from the NRD. ICD-9-CM and the Healthcare Cost and Utilization Project Clinical Classification Software codes used to identify comorbidities and procedures are available in Supplementary Table 1 .
The primary outcomes of this study were crude and risk-adjusted rate of HF hospitalization within 6 months (180 days) from discharge after an AMI in patients with and without renal injury. Outcomes were evaluated in the categories of patients without any renal injury, AKI without baseline CKD Stages III to V, stable CKD, AKI on CKD Stages III to V, and ESRD. The primary outcome was evaluated in subgroups of prespecified cardiovascular risk factors (age, gender, hypertension, diabetes mellitus, obesity, smoking, atrial fibrillation), AMI type, revascularization status, and in patients with and without HF at the time of index AMI. A composite outcome of 6-month HF readmission or all-cause mortality during a non–HF-related admission was studied in the overall cohort. This outcome was chosen to account for the competing risk of non-HF death on the risk for HF hospitalizations. The impact of a renal injury on the occurrence of death during a non–HF-related admission was also studied. Additional outcomes were differences in the crude rates of fatal HF readmission and the combined in-hospital HF during the index admission or a 6-month HF readmission outcome in patients with and without renal disease. HF hospitalizations were identified as those that had a primary discharge diagnosis of HF within 180 days from discharge ( Supplementary Table 1 ). Fatal HF hospitalization was defined as readmission primarily for HF during which the patient died.
The NRD has a complex semi-random multistage sampling survey design and surveys design-based statistical tests using weighted data were used for all analyses. Categorical variables are expressed as percentages, and continuous variables as mean ± SD. Baseline patient characteristics and outcomes were compared between patients across strata of renal injury using the Rao-Scott chi-square test for categorical variables and general linear models with analysis of variance for continuous variables; Table 1 . Differences in these characteristics based on the occurrence of a 6-month HF hospitalization, composite outcome, or death during a non-HF admission were studied using the Rao-Scott chi-square test for categorical variables and Student’s t test for continuous variables; Supplementary Tables 2 to 4 .
| Renal Disease | |||||||
|---|---|---|---|---|---|---|---|
| Variable | Total (n = 237,549) | None (n = 175,813) | AKI without CKD (n = 14,553) | Stable CKD (n = 20,922) | AKI on CKD (n = 18,282) | ESRD (N = 7,980) | p Value |
| Mean age [years (SD)] | 66.9 (13.8) | 64.9 (13.6) | 70.6 (13.1) | 75.5 (11.8) | 74.2 (12.0) | 66.7 (12.1) | <0.001 |
| Age (years) | <0.001 | ||||||
| 18–65 | 44.4% | 51.2% | 32.6% | 17.3% | 21.0% | 43.0% | |
| ≥65 | 55.6% | 48.8% | 67.4% | 82.7% | 79.0% | 57.0% | |
| Women | 37.9% | 37.0% | 39.4% | 41.0% | 40.5% | 41.6% | |
| Presenting diagnosis | <0.001 | ||||||
| STEMI | 28.1% | 32.8% | 20.4% | 14.9% | 12.9% | 8.4% | |
| Non-STEMI | 71.9% | 67.2% | 79.6% | 85.1% | 87.1% | 91.6% | |
| Median household income (quartile) | <0.001 | ||||||
| 1st | 29.5% | 29.0% | 31.0% | 28.2% | 31.5% | 35.2% | |
| 2nd | 28.3% | 28.4% | 27.8% | 27.8% | 29.0% | 26.7% | |
| 3rd | 23.1% | 23.3% | 22.0% | 23.7% | 22.4% | 20.9% | |
| 4th | 19.1% | 19.3% | 19.1% | 20.3% | 17.2% | 17.2% | |
| Insurance status | <0.001 | ||||||
| Insured | 94.7% | 93.5% | 96.2% | 98.7% | 98.2% | 99.4% | |
| Uninsured | 5.3% | 6.5% | 3.8% | 1.3% | 1.8% | 0.6% | |
| Comorbidities | |||||||
| Hypertension | 74.5% | 71.4% | 73.1% | 87.6% | 84.2% | 88.9% | <0.001 |
| Dyslipidemia | 66.4% | 67.3% | 58.9% | 68.7% | 64.8% | 59.1% | <0.001 |
| Atrial fibrillation | 16.9% | 13.9% | 25.0% | 25.6% | 26.8% | 23.5% | <0.001 |
| Carotid artery disease | 2.4% | 2.0% | 3.4% | 3.9% | 4.1% | 3.0% | <0.001 |
| Diabetes mellitus | 37.3% | 31.5% | 42.3% | 51.9% | 58.2% | 69.6% | <0.001 |
| Anemia | 16.5% | 9.5% | 23.7% | 28.4% | 41.5% | 67.0% | <0.001 |
| Cancer | 2.9% | 2.6% | 3.9% | 3.8% | 3.8% | 2.2% | <0.001 |
| Coronary artery disease | 82.0% | 83.1% | 74.4% | 81.5% | 77.8% | 82.0% | <0.001 |
| Connective tissue disease | 2.6% | 2.5% | 3.4% | 3.3% | 2.9% | 2.5% | <0.001 |
| Chronic Obstructive Pulmonary Disease | 20.8% | 18.9% | 26.0% | 25.8% | 28.0% | 23.5% | <0.001 |
| Previous stroke/TIA | 9.2% | 7.6% | 11.0% | 14.9% | 15.0% | 14.4% | <0.001 |
| Previous myocardial infarction | 12.6% | 11.6% | 11.9% | 18.4% | 15.1% | 15.8% | <0.001 |
| Previous coronary revascularization | 22.1% | 20.0% | 20.9% | 32.0% | 27.4% | 31.3% | <0.001 |
| Smoking | 43.9% | 47.4% | 36.8% | 34.2% | 32.9% | 28.7% | <0.001 |
| Depression | 8.4% | 8.1% | 8.8% | 9.4% | 8.8% | 8.8% | 0.002 |
| Drug abuse | 2.8% | 3.1% | 3.5% | 1.5% | 1.9% | 1.9% | <0.001 |
| Hypothyroidism | 11.7% | 10.2% | 13.1% | 17.9% | 16.4% | 14.9% | <0.001 |
| Liver disease | 1.6% | 1.4% | 2.4% | 1.6% | 2.4% | 3.4% | <0.001 |
| Fluid and electrolyte disorders | 21.3% | 15.7% | 46.0% | 21.5% | 45.5% | 44.4% | <0.001 |
| Obesity | 17.4% | 17.2% | 18.4% | 17.2% | 19.3% | 17.0% | <0.001 |
| Peripheral vascular disease | 12.2% | 9.3% | 14.0% | 21.9% | 21.7% | 27.0% | <0.001 |
| In-hospital Complications and Procedures | |||||||
| HF during index admission | 29.2% | 20.4% | 48.4% | 47.7% | 65.1% | 58.2% | <0.001 |
| PCI | 53.1% | 59.8% | 35.2% | 36.5% | 29.5% | 34.9% | <0.001 |
| CABG | 9.3% | 9.1% | 15.4% | 6.0% | 10.2% | 10.0% | <0.001 |
| Coronary revascularization | 61.7% | 68.1% | 49.6% | 42.2% | 39.4% | 44.5% | <0.001 |
| Disposition | <0.001 | ||||||
| Home | 87.9% | 91.7% | 75.5% | 81.7% | 72.6% | 77.9% | |
| Short term hospital, nursing home, or other facility | 12.1% | 8.3% | 24.5% | 18.3% | 27.4% | 22.1% | |
| Hospital characteristics | |||||||
| Teaching | 64.2% | 64.0% | 68.0% | 61.7% | 64.2% | 67.9% | <0.001 |
| Bed size | <0.001 | ||||||
| Small | 11.6% | 11.5% | 11.4% | 14.3% | 10.4% | 10.2% | |
| Medium | 27.3% | 27.4% | 24.9% | 28.6% | 27.5% | 25.0% | |
| Large | 61.1% | 61.1% | 63.7% | 57.2% | 62.0% | 64.8% | |
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