There are limited contemporary data available describing recent trends in the magnitude and characteristics of patients who are rehospitalized multiple times after hospital discharge for an acute myocardial infarction (AMI). We reviewed the medical records of 4,480 residents of the Worcester, Massachusetts, metropolitan area, who were discharged from 3 Central Massachusetts medical centers after an AMI in 6 biennial periods from 2001 to 2011 and were followed for all-cause and cause-specific hospital readmissions over the subsequent 6 months. The average age of our study population was 68 years, 89% were white, and 41% were women. Overall, ∼1 of every 3 patients had a readmission to the hospital within 6 months after hospital discharge for an AMI. The proportion of patients who were readmitted to the hospital 1, 2, or 3 times for any cause within 6 months remained unchanged during the years under study (20%, 8%, and 6%, respectively); 59% of these readmissions were cardiac related. Women, elderly patients, those with multiple chronic conditions, patients with a prolonged index hospitalization, and those who developed heart failure and/or atrial fibrillation during hospitalization were at higher risk for being readmitted multiple times compared with those who were readmitted once. Six-month hospital readmission rates after hospital discharge for an AMI remained stable during the years under study. In conclusion, we identified several groups at higher risk for multiple hospital readmissions who might be targeted for intensified monitoring efforts and tailored educational and treatment approaches.
Acute myocardial infarction (AMI) accounts for most cardiovascular disease (CVD)–related hospitalizations in American adults. Hospital readmissions after discharge for AMI have been targeted for public reporting because these repeat health encounters are a common, costly, and often preventable outcome. Readmissions to the hospital not only have a significant impact on patients’ health and functional status after AMI but also act as an indicator of hospital quality of care. Although several observational studies have examined hospital readmission rates for up to 30-day post-hospital discharge for AMI, there is a lack of relatively contemporary data describing the development of multiple hospital readmissions after a more extended period after hospital discharge for AMI, the reasons for these readmissions, and the characteristics of persons at increased risk for multiple rehospitalizations. Using data from the Worcester Heart Attack Study, we examined overall and decade-long trends (2001 to 2011) in the magnitude, reasons for, and patient characteristics associated with multiple hospital readmissions during the first 6 months after hospital discharge for AMI.
Methods
Data for this study were derived from the Worcester Heart Attack Study. This is an ongoing population-based investigation that is examining long-term trends in the incidence rates, hospital, and post-discharge case-fatality rates of AMI among residents of the Worcester (Massachusetts) metropolitan area. Only patients who had survived their index hospitalization for AMI at the 3 largest tertiary care and community medical centers in Central Massachusetts, which comprise the vast majority of all hospital (∼90%) admissions for AMI among residents of Central Massachusetts and were discharged from the hospital on a biennial basis from 2001 to 2011, were included in the present study.
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 AMI were independently validated using predefined criteria for AMI. Diagnoses of ST-segment elevation myocardial infarction and non–ST-segment elevation myocardial infarction were made using standardized criteria. Trained nurses and physicians abstracted demographic and clinical data from patient’s hospital medical records. Information about the hospital use of important cardiac medications, coronary angiography, percutaneous coronary intervention (PCI), and coronary artery bypass graft surgery was also collected as was information about the development of several significant clinical complications (e.g., atrial fibrillation, cardiogenic shock, stroke, heart failure) during the patient’s index hospitalization.
A hospital readmission was defined as the first, second, or third readmission to a participating study hospital within 6 months of discharge after the patient’s index hospitalization. Due to funding constraints, we only examined up to 3 readmissions to the hospital during this high-risk transition period. Readmission data were abstracted from the electronic medical records data warehouse at our principal study sites, namely the University of Massachusetts-Memorial Medical Center and Saint Vincent Hospital. A staged PCI was not counted as a hospital readmission. Two investigators adjudicated whether the principal reason for the hospital readmission was CVD or non-CVD related. Indications for CVD-related hospitalizations included conditions, such as an acute coronary syndrome, heart failure, and chronic ischemic heart disease. Examples of non–CVD-related hospitalizations included urinary tract infections, hemorrhage, and bone fractures. This study was approved by the Institutional Review Board at the University of Massachusetts Medical School.
Differences in the characteristics of patients with none, 1, 2, or 3 subsequent readmissions to the 3 major teaching and community hospitals in Central Massachusetts during the subsequent 6 months were examined through the use of chi-square tests for categorical variables and ANOVA for continuous variables. For ease of analysis and interpretation, trends in 6-month hospital readmission rates were examined during the aggregated study years of 2001/2003 “earliest,” 2005/2007 “middle,” and 2009/2011 “most recent.” Crude and multivariable adjusted multinomial logistic regression analyses were used to examine demographic, clinical, and other factors associated with the risk of having none, few, or multiple readmissions after adjusting for several potentially confounding variables. Our results were presented as multivariable-adjusted odds ratios and accompanying 95% confidence intervals.
Results
The present study sample included only patients who survived their index hospitalization for AMI and the full 6-month at-risk period (n = 4,480; ∼12% of patients died during this period). This included 1,798 patients in 2001/2003, 1,419 patients in 2005/2007, and 1,263 patients in 2009/2011. The average age of this population was 68 years, 41% were women, and 89% were white.
Approximately 19.9%, 8.0%, and 5.6% of patients were readmitted to participating study hospitals once, twice, or 3 times within 6 months of discharge after their index AMI, respectively; approximately two thirds of our study population were “readmission free” during the years under study. The 6-month hospital readmission rates remained essentially unchanged during the years under study ( Table 1 ).
| Study Period | Number of Rehospitalizations | |||||
|---|---|---|---|---|---|---|
| % | 1 ORs (95% CI) n=884 | % | 2 ORs (95% CI) n=361 | % | 3 ORs (95% CI) n=252 | |
| 2001/2003 | 20.9 | 1.00 | 8.9 | 1.00 | 5.4 | 1.00 |
| 2005/2007 | 21.6 | 1.12 (0.93-1.35) | 8.9 | 0.90 (0.69-1.18) | 6.1 | 0.91 (0.66-1.25) |
| 2009/2011 | 22.0 | 1.07 (0.87-1.31) | 6.1 | 0.85 (0.63-1.14) | 5.2 | 0.92 (0.66-1.30) |
We examined the risk of being hospitalized once, twice, or 3 times during earlier compared with the most recent years under study after controlling for a number of potentially confounding variables that might have affected the risk of being rehospitalized. After multivariable adjustment, there was no significant change in the odds of experiencing 1, 2, or 3 subsequent readmissions during 2005/2007 and 2009/2011 compared with the referent period of 2001/2003 ( Table 1 ).
Among patients who were readmitted to the hospital during the years under study, 59.1% were readmitted because of a CVD-related condition. Among those who were rehospitalized once during the subsequent 6 months, 58.8% of these readmissions were CVD related; this proportion was 61.3% for those who were readmitted twice during the subsequent 6 months and 56.8% for those who were readmitted 3 times during this period.
Overall, slightly older patients and women were more likely to have 3 readmissions over the subsequent 6 months compared with those with none or fewer readmissions ( Table 2 ). Patients with multiple readmissions were more likely to have been previously diagnosed with several chronic conditions and were less likely to have developed an incident AMI compared with those who were not readmitted to participating hospitals ( Table 2 ). Patients who were readmitted 3 times had a longer average index hospital stay and were more likely to have developed heart failure and/or atrial fibrillation during their acute hospitalization than those who were not re-hospitalized or had fewer readmissions during the follow-up period ( Table 2 ).
| Variable | Number of Rehospitalizations | |||
|---|---|---|---|---|
| None N= 2,983 | 1 N=884 | 2 N= 361 | 3 N=252 | |
| Age (years [mean, SD]) | 66.4±14.1 | 70.1± 13.3 | 69.9± 13.4 | 70.9± 12.5 ∗ |
| Men | 1,859 (62.3%) | 483(54.6%) | 191(52.9%) | 116(46.0%) † |
| Do not resuscitate orders | 348 (11.7%) | 132(14.9%) | 65(18.0%) | 35(13.9%) † |
| ST-segment myocardial infarction | 1,079(36.2%) | 275(31.1%) | 105(29.1%) | 57(22.6%) † |
| Body mass index (kg/m 2 [mean, SD]) | 28.5±6.0 | 28.5±6.5 | 28.6±6.4 | 27.9±6.6 |
| Acute myocardial infarction | 2,116(70.9%) | 546(61.8%) | 209(57.9%) | 130(51.6%) † |
| Anemia | 202(6.8%) | 92(10.4%) | 49(13.6%) | 50(19.8%) † |
| Atrial fibrillation | 261(8.8%) | 142(16.1%) | 56(15.5%) | 54(21.4%) † |
| Chronic kidney disease | 364(12.2%) | 175(19.8%) | 95(26.3%) | 75(29.8%) † |
| Chronic obstructive pulmonary disease | 392(13.1%) | 167(18.9%) | 68(18.8%) | 70(27.8%) † |
| Diabetes mellitus | 851(28.5%) | 346(39.1%) | 127(42.4%) | 127(50.4%) † |
| Heart failure | 398(13.3%) | 226(25.6%) | 91(25.2%) | 97(38.5%) † |
| Hypertension | 2,074(69.5%) | 676(76.5%) | 291(80.6%) | 205(81.4%) † |
| Peripheral vascular disease | 353(11.8%) | 168(19.0%) | 98(27.2%) | 86(34.1%) † |
| Stroke | 242(8.1%) | 86(9.7%) | 54(15.0%) | 44(17.5%) † |
| Current smoker | 795(26.7%) | 187(21.2%) | 85(23.6%) | 58(23.0%) |
| Number of morbidities | ||||
| None | 619(20.8%) | 103(11.7%) | 23(6.4%) | 13(5.2%) † |
| 1 | 929(31.1%) | 214(24.2%) | 90(24.9%) | 37(14.7%) ∗ |
| 2 | 704(23.6%) | 198(22.4%) | 73(20.2%) | 52(20.6%) ∗ |
| 3 | 355(11.9%) | 175(19.8%) | 72(19.9%) | 40(15.8%) † |
| ≥ 4 | 376(12.6%) | 194(22.0%) | 103(28.5%) | 110(43.7%) † |
| Length of stay during index hospitalization (days [mean, SD]) (days) | 4.8± 5.0 | 5.8± 4.9 | 5.9± 4.7 | 6.1± 4.9 † |
| Glomerular filtration rate (ml/min/1.73m 2 [mean, SD]) | 62.3±19.8 | 56.2± 20.5 | 53.7± 21.9 | 52.3± 21.4 ∗ |
| Systolic blood pressure(mm Hg [mean ,SD]) | 144.3±30.2 | 143.8± 31.3 | 145.3± 32.6 | 145.2± 35.2 |
| Diastolic blood pressure(mm Hg [mean, SD]) | 80.3± 18.7 | 77.2± 18.5 | 76.5± 20.0 | 76.2± 20.4 † |
| Glucose (mg/dl [mean, SD]) | 161.7± 73.1 | 172.5± 80.9 | 183.1± 87.6 | 179.4± 85.4 † |
| Total cholesterol(mg/dl [mean, SD]) | 175.7± 43.9 | 166.5± 45.3 | 169.3± 50.0 | 164.9± 44.7 |
| Hemoglobin (g/dl [mean, SD]) | 14.4±3.2 | 13.4±5.0 | 13.1±2.8 | 12.7±2.2 † |
| Complications during hospitalization | ||||
| Atrial fibrillation | 422(14.2%) | 179(20.3%) | 65(18.0%) | 65(25.8%) † |
| Cardiogenic shock | 68 (2.3%) | 31(3.5%) | 15(4.2%) | 9(3.6%) |
| Heart failure | 1,078(36.1%) | 421(47.6%) | 179(49.6%) | 151(59.9%) † |
| Stroke | 24(0.8%) | 13(1.5%) | 6(1.7%) | 5(2.0%) |
The proportion of patients who received evidence-based inhospital medications and cardiac interventions was similar for those with and without multiple readmissions; however, a slightly higher proportion of patients who were readmitted 3 times received angiotensin-converting enzyme inhibitors. In contrast, a lower proportion of patients with 3 readmissions underwent cardiac catheterization and/or a PCI during their index hospitalization compared with those who were not re-admitted or had fewer readmissions during this period ( Table 3 ).
| Variable | Number of Rehospitalizations | |||
|---|---|---|---|---|
| None N= 2,983 | 1 N=884 | 2 N= 361 | 3 N=252 | |
| Cardiac medications during hospitalization | ||||
| ACE-I/ARBs | 1,988(66.6%) | 612(69.2%) | 240(66.5%) | 193(76.6%) ∗ |
| Aspirin | 2,870(96.2%) | 848(95.9%) | 340(94.2%) | 243(96.4%) |
| Beta-blockers | 2,819(94.5%) | 838(94.8%) | 343(95.0%) | 240(95.2%) |
| Lipid-lowering agents | 2,466(82.7%) | 723(81.8%) | 290(80.3%) | 207(82.1%) |
| Interventions | ||||
| Cardiac catheterization | 2,209(74.1%) | 621(70.3%) | 217(60.1%) | 150(59.5%) † |
| Coronary bypass | 242(8.1%) | 69(7.8%) | 26(7.2%) | 9(3.6%) |
| Percutaneous coronary intervention | 1,606(53.8%) | 437(49.4%) | 158(43.8%) | 99(39.3%) † |
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