There are limited data available describing relatively contemporary trends in 90-day rehospitalizations in patients who survive hospitalization after an acute myocardial infarction (AMI) in a community setting. We examined decade-long (2001 to 2011) trends in, and factors associated with, 90-day rehospitalizations in patients discharged from 3 central Massachusetts (MA) hospitals after AMI. Residents of the Worcester, MA, metropolitan area discharged after AMI from 3 central MA hospitals on a biennial basis from 2001 to 2011 comprised the study population (n = 4,810). The average age of this population was 69 years, 42% were women, and 92% were white. From 2001 to 2011, 30.0% of patients were rehospitalized within 90 days after hospital discharge, and 38% of 90-day rehospitalizations occurred after the first month after hospital discharge. Crude 90-day rehospitalization rates decreased from 31.5% in 2001/2003 to 27.3% in 2009/2011. After adjusting for several sociodemographic characteristics, co-morbidities, and in-hospital factors, there was a reduced risk of being rehospitalized within 90 days after hospital discharge in 2009/2011 compared with 2001/2003 (risk ratio = 0.87, 95% CI = 0.77 to 0.98); this trend was slightly attenuated (risk ratio = 0.90, 95% CI = 0.79 to 1.02) after further adjustment for hospital treatment practices. Female sex, having several previously diagnosed co-morbidities, an increased hospital stay, and the in-hospital development of atrial fibrillation, cardiogenic shock, and heart failure were significantly associated with an increased risk of being rehospitalized. In conclusion, the likelihood of subsequent 90-day rehospitalizations remained frequent, and we did not observe a significant decrease in these rates during the years under study.
Owing to current hospital reimbursement policies that enforce penalties on excess 30-day readmissions, several studies have reported 30-day rehospitalization rates and associated risk factors in patients surviving hospitalization for acute myocardial infarction (AMI). However, little is known about recent trends in 90-day rehospitalization rates, the reasons for rehospitalization and risk factors that may affect 90-day rehospitalization rates in patients surviving an AMI. Our primary study objective was to describe decade-long (2001 to 2011) trends in the frequency of having a first rehospitalization within 90 days of discharge in patients surviving hospitalization for an AMI. Our secondary study objective was to describe the reasons for being rehospitalized, and factors associated with an increased risk of 90-day rehospitalizations, among residents of central Massachusetts (MA) discharged from the 3 principal medical centers in central MA after an AMI.
Methods
Described elsewhere in detail, the Worcester Heart Attack Study is a population-based investigation examining long-term trends in the descriptive epidemiology of AMI in residents of the Worcester, MA, metropolitan area (2010 census = 518,000) hospitalized at all 16 medical centers in central MA on an approximate biennial basis from 1975 to 2011. Owing to hospital closures, mergers, or conversion to long-term care facilities, fewer hospitals (n = 11) have been providing care to greater Worcester residents since the 1990s.
Computerized printouts of patients discharged from all greater Worcester hospitals with possible AMI ( International Classification of Disease, Ninth Revision codes: 410 to 414, 786.5) were identified and cases of possible AMI were independently validated using predefined criteria for AMI. These criteria included a suggestive clinical history, increases in several serum biomarkers, and serial electrocardiographic findings during hospitalization consistent with the presence of AMI. Patients who satisfied at least 2 of these 3 criteria, and were residents of the Worcester metropolitan area because this study is population-based, were included.
Because the focus of the present study was rehospitalization after hospital discharge for AMI, we included adult residents of the Worcester metropolitan area who survived their index hospitalization for AMI 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 were discharged from these facilities. The patient’s index hospitalization and any subsequent readmission occurred in any of the 3 study hospitals. Patients who had their index hospitalization or their rehospitalization outside these 3 major medical centers were not included. This study was approved by the Institutional Review Board at the University of Massachusetts Medical School.
Trained nurses and physicians abstracted data on patient’s sociodemographic characteristics, medical history, clinical data, and treatment practices through the review of hospital medical records. These factors included patient’s age, gender, race, marital status, year of hospitalization, hospital length of stay, history of several previously diagnosed co-morbidities (e.g., stroke, hypertension, and diabetes mellitus), AMI order (initial vs previous) and AMI type (ST-segment elevation myocardial infarction [STEMI] versus non-STEMI). Information on the development of important in-hospital complications (e.g., atrial fibrillation, cardiogenic shock, heart failure, and stroke ) was also collected.
Data on the receipt of thrombolytic therapy and 3 coronary diagnostic and interventional procedures (cardiac catheterization, percutaneous coronary intervention (PCI), and coronary artery bypass grafting) during hospitalization, and medications prescribed at the time of hospital discharge, including 4 effective cardiac medications (angiotensin-converting inhibitors/angiotensin receptor blockers, aspirin, β blockers, and lipid-lowering agents), were obtained.
A rehospitalization was defined as the patient’s first readmission to a study hospital within 90 days of hospital discharge after AMI. Two independent investigators adjudicated whether the principal reason for readmission was either cardiovascular disease (CVD) or non-CVD related based on information contained in hospital medical records. Indications for CVD-related hospitalizations included an acute coronary syndrome, heart failure, the type 2 diabetes mellitus, and chronic ischemic heart disease. Examples of non-CVD–related hospitalizations included urinary tract infections, hemorrhage, osteoarthritis, and bone fractures.
For ease of analysis and interpretation, we aggregated the 6 individual study years into 3 2-year strata (2001/2003, earliest; 2005/2007, middle; and 2009/2011, most recent) for purposes of examining trends in our principal study outcome. Differences in the distribution of patient sociodemographic and clinical characteristics between patients hospitalized during the 3 aggregated periods were examined using the analysis of variance or Kruskal–Wallis tests for continuous variables and the chi-square test for categorical variables. The Cochran–Armitage tests and linear or quantile regression models were used to assess for linear trends over time among categorical and continuous variables, respectively.
Postdischarge rehospitalization rates were examined by calculating the frequency of having a first rehospitalization within 90 days in patients discharged from the hospital after their index AMI. We examined average weekly rates of being rehospitalized during the first 90 days after hospital discharge. We also examined the reasons for being rehospitalized during this period and calculated the cause-specific 90-day rehospitalization rates. Multivariable-adjusted Poisson regression models with robust error variance were used to examine the association between period of hospitalization and the outcome of whether the patient was rehospitalized during the following 90 days while adjusting for several potentially confounding variables of prognostic importance.
Several covariates associated with rehospitalization after AMI in previous studies were examined including age, gender, race, marital status, AMI order and type, previously diagnosed co-morbid conditions, hospital clinical complications, and hospital length of stay. We further adjusted for hospital treatment practices (i.e., thrombolytic therapy, cardiac catheterization, PCI, and coronary artery bypass grafting surgery and the prescribing of angiotensin-converting inhibitors/angiotensin receptor blockers, aspirin, β blockers, and lipid-lowering agents at the time of hospital discharge) during the patient’s index hospitalization to examine their potential effects on 90-day rehospitalization trends. We repeated the same analyses after excluding patients (n = 246) who were not rehospitalized but died during the 90-day postdischarge period or by treating patients who were not rehospitalized but died within the 90-day postdischarge period as those who had a 90-day readmission. The results were presented as multivariable-adjusted risk ratios (RRs) and accompanying 95% CIs.
Results
The study population consisted of 4,810 adult residents of the Worcester metropolitan area who survived their hospitalization for AMI at the 3 major central MA medical centers from 2001 to 2011 ( Table 1 ). Overall, the average age of this population was 68.9 years, 41.8% were women, 92.4% were white, and 54.6% were married.
| Variable | 2001/2003 (n=1,923) | 2005/2007 (n=1,517) | 2009/2011 (n=1,370) | P-value ∗ | P for trend † |
|---|---|---|---|---|---|
| Age, mean (years) | 70.8 | 69.2 | 65.7 | <.001 | <.001 |
| Age <55 years | 15.2% | 18.1% | 23.1% | <.001 | |
| Age 55-64 years | 17.5% | 19.3% | 23.0% | ||
| Age 65-74 years | 21.6% | 20.0% | 24.5% | ||
| Age 75-84 years | 28.0% | 28.0% | 21.5% | ||
| Age ≥85 years | 17.7% | 14.6% | 7.9% | ||
| Female | 42.8% | 41.9% | 40.3% | 0.35 | 0.16 |
| White | 94.0% | 91.7% | 91.1% | <.005 | 0.002 |
| Married | 53.7% | 54.4% | 56.1% | 0.40 | 0.19 |
| Hospital length of stay, median (IQR) (days) | 5 (3-8) | 4 (3-6) | 3 (2-5) | <.001 | <.001 |
| Angina pectoris | 22.5% | 12.9% | 4.6% | <.001 | <.001 |
| Atrial fibrillation | 14.1% | 12.9% | 13.0% | 0.50 | 0.33 |
| Heart failure | 22.6% | 24.3% | 19.6% | 0.01 | 0.08 |
| Hypertension | 71.0% | 75.4% | 75.4% | <.005 | 0.003 |
| Peripheral vascular disease | 14.9% | 20.4% | 19.9% | <.001 | <.001 |
| Stroke | 11.5% | 10.8% | 9.8% | 0.28 | 0.11 |
| Diabetes mellitus | 33.0% | 34.4% | 37.4% | 0.028 | 0.009 |
| Chronic obstructive pulmonary disease | 18.3% | 15.7% | 15.8% | 0.06 | 0.041 |
| Depression | 15.5% | 16.7% | 17.5% | 0.29 | 0.12 |
| Chronic kidney disease | 15.8% | 22.3% | 22.3% | <.001 | <.001 |
| ST-segment myocardial infarction | 34.0% | 32.2% | 31.1% | 0.19 | 0.07 |
| Initial myocardial infarction | 65.0% | 64.9% | 64.8% | 0.99 | 0.91 |
| In-hospital clinical complications | |||||
| Atrial fibrillation | 20.9% | 19.9% | 14.5% | <.001 | <.001 |
| Cardiogenic shock | 3.4% | 4.1% | 3.0% | 0.26 | 0.66 |
| Stroke | 1.8% | 0.5% | 1.8% | <.001 | 0.83 |
| Heart failure | 37.9% | 36.4% | 27.5% | <.001 | <.001 |
| In-hospital management | |||||
| Cardiac catheterization | 62.1% | 74.9% | 76.1% | <.001 | <.001 |
| Percutaneous coronary intervention | 41.4% | 55.5% | 60.0% | <.001 | <.001 |
| Coronary artery bypass grafting | 8.3% | 6.3% | 7.2% | 0.09 | 0.17 |
| Thrombolytic therapy | 6.3% | 0.5% | 0.2% | <.001 | <.001 |
| Medication at hospital discharge | |||||
| Angiotensin converting enzyme inhibitors/Angiotensin receptor blockers | 59.3% | 68.6% | 64.8% | <.001 | <.001 |
| Aspirin | 83.2% | 92.4% | 93.2% | <.001 | <.001 |
| Beta blockers | 83.1% | 91.0% | 89.7% | <.001 | <.001 |
| Lipid-lowering agents | 65.6% | 79.1% | 88.8% | <.001 | <.001 |
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