There are limited contemporary data available describing the characteristics of patients who neither died nor were readmitted to the hospital during the first year after hospital discharge for an acute myocardial infarction (AMI) in comparison with those who died and/or were readmitted to the hospital during this high-risk period. Residents of the Worcester, Massachusetts, metropolitan area discharged after an AMI from 3 central Massachusetts hospitals on a biennial basis from 2001 to 2011 comprised the study population. The average age of this population (n = 4,268) was 69 years, 62% were men, and 92% were white. From 2001 to 2011, 43.5% of patients were classified as low-risk survivors of an AMI, 12.3% died, and 44.2% did not die but had at least 1 rehospitalization during the subsequent year. The proportion of low-risk survivors increased from 42.6% to 46.4%, whereas the proportion of those who died within a year after hospital discharge decreased from 14.3% to 10.5%, respectively, during the years under study. After adjusting for several patient characteristics, younger (≤65 years) persons, men, those who were married, those who did not present with multimorbidities, and patients who did not develop in-hospital clinical complications were more likely to be classified as a low-risk AMI survivor. Identifying low-risk survivors of an AMI may help health care providers to focus more intensive efforts and interventions on those at higher risk for dying and/or being readmitted to the hospital during the postdischarge transition period after an AMI.
Acute myocardial infarction (AMI) is a common manifestation of underlying coronary artery disease which affected more than 800,000 American adults in 2010. Although significant improvements in the care of patients hospitalized with AMI have taken place over the past several decades, there are still some gaps in the published reports identifying those at a lower risk for dying or being readmitted to the hospital after an AMI. Most studies that has examined the characteristics of those who died after hospital discharge for an AMI have focused on the role of important risk and prognostic factors including cigarette smoking, overweight or obesity, and extent and severity of underlying coronary disease. However, few contemporary studies have described the characteristics of those who either survived an AMI and/or were not readmitted to the hospital during the high-risk first year after hospital discharge for an AMI. The objectives of this investigation were to describe the characteristics of those who survived and were not readmitted to the hospital during the first year after hospital discharge for an AMI compared with those who died and/or were readmitted to the hospital during this period.
Methods
Described elsewhere in detail, the Worcester Heart Attack Study is an ongoing population-based investigation that is examining long-term trends in the epidemiology of AMI in residents of the Worcester, Massachusetts (MA), metropolitan area (2010 census = 518,000) hospitalized at all medical centers in central MA on an approximate biennial basis.
Computerized printouts of patients discharged from all greater Worcester hospitals with possible AMI were identified, and cases of AMI were independently validated using predefined criteria. Diagnoses of ST-segment elevation myocardial infarction (STEMI) and non–ST-segment elevation myocardial infarction (NSTEMI) were made using standardized criteria.
We restricted our sample to adult residents of central MA who survived their index hospitalization for AMI and did not have do-not-resuscitate orders issued at that time, on a biennial basis from 2001 to 2011. We further restricted our study population to patients hospitalized at the 3 largest tertiary care and community medical centers in central MA. This was done because the majority (approximately 90%) of patients hospitalized for AMI in central MA was discharged from these facilities. This study was approved by the Institutional Review Board at the University of Massachusetts Medical School.
Trained nurses and physicians abstracted information on patient’s demographic and clinical characteristics and hospital treatment practices through the review of hospital medical records. These factors included patient’s age, gender, race or ethnicity, hospital length of stay, history of previously diagnosed co-morbidities (e.g., stroke, diabetes, heart failure), and AMI type (STEMI vs NSTEMI) and order (initial vs previous). Information on the development of important in-hospital complications including atrial fibrillation, cardiogenic shock, heart failure, stroke, and ventricular tachycardia was also collected.
Data on the receipt of thrombolytic therapy and 3 coronary diagnostic and interventional procedures (cardiac catheterization, percutaneous coronary intervention, and coronary artery bypass grafting [CABG]) during hospitalization and effective pharmacotherapies at the time of hospital discharge, namely angiotensin-converting inhibitors or angiotensin receptor blockers, aspirin, β blockers, and lipid-lowering agents, were also obtained.
The approaches used to ascertain survival status after hospital discharge included a review of records for additional hospitalizations and a statewide and national search of death certificates for residents of the Worcester metropolitan area; follow-up was continued through 2013. A rehospitalization was defined as the patient’s first admission for any reason to a study hospital within a year of discharge after their index hospitalization for AMI during the years under study. Two investigators adjudicated whether the principal reason for the hospital readmission was cardiovascular disease (CVD) or non-CVD related. Indications for CVD-related hospitalizations included conditions such as an acute coronary syndrome or heart failure. Examples of non–CVD-related hospitalizations included urinary tract infections, hemorrhage, and bone fractures. We compared the characteristics of those who survived and were not readmitted to the hospital during their first year after discharge with those who died (comparison group) and with those who died and had at least 1 readmission for any reason to the hospital during this at risk period (second comparison group). We hypothesized that the characteristics of these 2 comparison groups would be different and would provide useful information when designing future interventions and clinical management of these different groups.
One-year rehospitalization rates were examined by calculating the frequency of having a rehospitalization within 365 days in patients discharged from the hospital after their index AMI during the years under study; similar methods were used to calculate 1-year death rates. Differences in the distribution of various patient demographic and clinical characteristics between our case and 2 comparison groups were examined using the analysis of variance test for continuous variables and the chi-square test for categorical variables. Several covariates associated with rehospitalization or death in previous studies were examined. These included age, gender, marital status, AMI type (STEMI vs NSTEMI), previously diagnosed co-morbid conditions (e.g., angina, atrial fibrillation, heart failure, hypertension, stroke, diabetes, chronic obstructive pulmonary disease, and chronic kidney disease), hospital clinical complications (atrial fibrillation, heart failure, cardiogenic shock, ventricular tachycardia, and stroke), and hospital length of stay. Despite the potential for confounding by treatment indication, we further examined the role of several hospital treatment practices, including the receipt of thrombolytic therapy and 3 coronary interventional procedures (cardiac catheterization, percutaneous coronary intervention, and coronary artery bypass grafting), and prescribing of 4 guideline-recommended cardiac medications (angiotensin-converting inhibitors or angiotensin receptor blockers, aspirin, β blockers, and lipid-lowering agents) at the time of hospital discharge in relation to the risk of rehospitalization and/or death.
For ease of analysis and interpretation of our trend findings, we aggregated the 6 individual study years into three 2-year strata (2001 to 2003, 2005 to 2007, and 2009 to 2011).
Multivariate adjusted logistic regression analyses were performed to examine the association between demographic and clinical variables and the outcome of whether the patient survived the first year after hospital discharge for AMI. We further categorized the co-morbidities and complications by number of conditions and repeated the same multivariate adjusted logistic regression analyses. Our results were presented as multivariate adjusted odds ratios and accompanying 95% confidence intervals.
Results
The study population consisted of a total of 4,268 patients with an independently validated AMI. Of these, 43.5% were classified as low-risk survivors (survived for 1 year without any readmissions to the hospital), 44.2% patients survived and had at least 1 readmission to the hospital for any reason during the first year after hospital discharge, and 12.3% of patients died with or without a readmission to the hospital during the first year after being discharged from the hospital after an AMI. From 2001/2003 to 2009/2011, the proportion of low-risk survivors of an AMI slightly increased from 42.6% to 46.4%, whereas the proportion of those who died within a year after hospital discharge decreased from 14.3% to 10.5%, respectively.
Low-risk survivors were approximately 12 years younger on average, included a greater proportion of men, those who were married, presented with an initial AMI, and patients who were more likely to have been diagnosed with an STEMI than the 2 comparison groups ( Table 1 ). Low-risk survivors were less likely to have been previously diagnosed with any of the co-morbidities examined, with the exception of hyperlipidemia. The average hospital stay was significantly shorter in the low-risk, long-term, survivors. Low-risk survivors presented with greater average blood pressures, glomerular filtration rate, and average initial serum cholesterol values but lower initial serum glucose findings, compared with our comparison groups ( Table 1 ). Low-risk survivors of an AMI were significantly less likely to have developed each of the in-hospital complications examined during their acute hospitalization ( Table 1 ).
| Characteristic | Survived without any hospital readmissions (n=1,855) | Survived with 1 hospital readmission (n=1,887) | Died with/without any hospital readmission (n=526) |
|---|---|---|---|
| Age (mean, years) (SD) | 63.2±13.2 | 67.8± 13.0 | 75.0± 11.1 ∗ |
| Men | 69.1% | 58.0% | 57.6% ∗ |
| Married | 63.1% | 54.3% | 47.5% ∗ |
| Body mass index (kg/m 2) (mean, SD) | 28.8± 5.7 | 28.9± 6.5 | 26.6± 5.9 ∗ |
| Non ST-segment myocardial infarction | 59.7% | 67.8% | 78.7% ∗ |
| Initial Acute Myocardial Infarction | 77.4% | 61.6% | 54.6% ∗ |
| Atrial fibrillation | 5.4% | 12.8 | 22.1 ∗ |
| Chronic kidney disease | 8.2% | 19.0 | 36.9 ∗ |
| Chronic lung disease | 10.2% | 17.7% | 24.0% ∗ |
| Diabetes mellitus | 24.9% | 40.1% | 47.7% ∗ |
| Heart failure | 7.6% | 20.8% | 42.2% ∗ |
| Hyperlipidemia+ | 62.5% | 65.8% | 59.7% † |
| Hypertension++ | 64.5% | 76.8% | 81.9% ∗ |
| Peripheral vascular disease | 8.7% | 19.9% | 31.8% ∗ |
| Stroke | 5.3% | 10.1% | 16.0% ∗ |
| Hospital length of stay (mean, days) (SD) | 4.4± 4.6 | 5.6± 4.8 | 7.0± 8.3 ∗ |
| Heart rate (mean, SD) | 92.0± 22.2 | 85.0± 21.7 | 81.5± 19.5 ∗ |
| Initial systolic blood pressure (mmHg) (mean, SD) | 144.2± 29.5 | 145.1± 31.4 | 139.7± 32.0 † |
| Diastolic systolic blood pressure (mmHg) (mean, SD) | 82.1± 18.1 | 78.3± 19.0 | 75.1± 19.9 † |
| Glomerular filtration rate (1.73 Ml/min) (mean, SD) | 65.7± 18.2 | 58.5± 21.0 | 47.2± 22.1 ∗ |
| Initial serum total cholesterol (mg/dl) (mean, SD) | 179.7± 43.4 | 169.6± 45.7 | 154.0± 44.2 |
| Initial serum glucose (mg/dl) (mean, SD) | 156.0± 69.3 | 171.3± 80.1 | 189.2± 89.2 ∗ |
| LDL-Cholesterol(mg/dl) (mean, SD) | 92.0± 42.7 | 100.5± 40.3 | 110.7± 39.6 |
| In-Hospital Clinical Complications | |||
| Atrial fibrillation | 11.0% | 18.0% | 29.5% ∗ |
| Cardiogenic shock | 2.3% | 3.1% | 7.4% ∗ |
| Heart failure | 31.0% | 42.6% | 62.7% ∗ |
| Stroke | 0.5% | 1.2% | 1.5% † |
| Ventricular tachycardia | 72.4% | 71.3% | 74.5% |
During the patient’s index hospitalization, low-risk survivors, and those who had at least 1 hospitalization during the following year, were significantly more likely to have been treated with aspirin, β blockers, and lipid-lowering medications compared with those who died ( Table 2 ). Low-risk survivors were significantly more likely to have undergone any of the cardiac interventional procedures during their acute hospitalization as compared with both comparison groups ( Table 2 ).
| Variable | Survived No readmissions (n=1,855) | Survived with 1 readmission (n=1,887) | Died with/without readmissions (n=526) |
|---|---|---|---|
| Diagnostic/Interventional Procedure | |||
| Cardiac catheterization | 81.0% | 76.8% | 45.6% ∗ |
| Percutaneous coronary intervention | 60.0% | 54.5% | 27.4% ∗ |
| Coronary bypass | 9.5% | 8.3% | 2.1% ∗ |
| Medications at discharge | |||
| Angiotensin converting enzyme inhibitors /Angiotensin receptor blockers | 66.7% | 69.6% | 67.3% |
| Aspirin | 96.4% | 96.0% | 91.8% ∗ |
| Beta blockers | 94.9% | 95.1% | 89.5% ∗ |
| Lipid lowering medications | 84.8% | 84.7% | 72.4% ∗ |
| Anticoagulants | 87.9% | 86.1% | 83.7% † |
After controlling for a variety of factors of prognostic importance, younger (<65 years) persons, men, those who were married, those who did not present with multimorbidities, those who presented with an initial AMI, and patients who did not develop any of the in-hospital clinical complications examined were more likely to be classified as a low-risk survivor ( Table 3 ). Differences in the receipt of various hospital treatment approaches between the 3 comparison groups were attenuated in the final adjusted models, but we continued to demonstrate greater receipt of effective medications and procedures in the low-risk group compared with those who died.
