Thirty-Day Readmission Risk Model for Older Adults Hospitalized With Acute Myocardial Infarction

Abstract

Background: Early readmissions among older adults hospitalized for acute myocardial infarction (AMI) are costly and difficult to predict. Aging-related functional impairments may inform risk prediction but are unavailable in most studies. Our objective was to, therefore, develop and validate an AMI readmission risk model for older patients who considered functional impairments and was suitable for use before hospital discharge.

Methods and results: SILVER-AMI (Comprehensive Evaluation of Risk in Older Adults with AMI) is a prospective cohort study of 3006 patients of age ≥75 years hospitalized with AMI at 94 US hospitals. Participants underwent in-hospital assessment of functional impairments including cognition, vision, hearing, and mobility. Other variables plausibly associated with readmissions were also collected. The outcome was all-cause readmission at 30 days. We used backward selection and Bayesian model averaging to derive (N=2004) a risk model that was subsequently validated (N=1002). Mean age was 81.5 years, 44.4% were women, and 10.5% were nonwhite. Within 30 days, 547 participants (18.2%) were readmitted. Readmitted participants were older, had more comorbidities, and had a higher prevalence of functional impairments, including activities of daily living disability (17.0% versus 13.0%; P=0.013) and impaired functional mobility (72.5% versus 53.6%; P<0.001). The final risk model included 8 variables: functional mobility, ejection fraction, chronic obstructive pulmonary disease, arrhythmia, acute kidney injury, first diastolic blood pressure, P2Y12 inhibitor use, and general health status. Functional mobility was the only functional impairment variable retained but was the strongest predictor. The model was well calibrated (Hosmer-Lemeshow P value >0.05) with moderate discrimination (C statistics: 0.65 derivation cohort and 0.63 validation cohort). Functional mobility significantly improved performance of the risk model (net reclassification improvement index =20%; P<0.001).

Conclusions: In our final risk model, functional mobility, previously not included in readmission risk models, was the strongest predictor of 30-day readmission among older adults after AMI. The modest discrimination indicates that much of the variability in readmission risk among this population remains unexplained by patient-level factors.

Clinical trial registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT01755052.

Keywords: acute kidney injury; aging; blood pressure; cardiac rehabilitation; myocardial infarction.

Figure 1.. SILVER-AMI study sites.

SILVER-AMI included 94 hospitals throughout the U.S.

Figure 2.. Timing of 30-day readmissions.

Kaplan-Meier curve for survival free from hospital readmission within 30 days of discharge. Among patients readmitted, median time to readmission was 10 days.

Figure 3.. Risk model elements: 30 day readmission.

After Bayesian model averaging with multivariable logistic regression, eight variables were retained in the final risk model. Functional mobility based on Timed Up and Go (TUG) with reference: TUG <15 seconds. Diastolic BP based on categories (in mmHg): <50, 50–59, 60–79, 80–89, 90–99, >100 with reference: <50. SF-12 general health status treated as four-level variable based on single question (“In general, would you say your health status is (1) excellent or very good; (2) good; (3) fair; (4) poor”) with reference: poor. Ejection fraction treated as four-level categorical variable (≥50%, 40–49%, 30–39%, <30%) with reference: <30%.

Figure 4.. Model calibration, validation cohort (by quintile).

Shown are observed (blue) and predicted (red) 30-day readmission rates, by quintiles of predicted readmission risk within the validation cohort. Among these quintiles, the SILVER-AMI readmission risk model was well calibrated (Hosmer-Lemeshow P > 0.05).

Figure 5.. SILVER-AMI 30-day readmission calculator.

A web-based calculator for predicted readmission risk among patients age ≥75 hospitalized for AMI is available at www.silverscore.org.