180-day readmission risk model for older adults with acute myocardial infarction: the SILVER-AMI study

Abstract

Objective: To develop a 180-day readmission risk model for older adults with acute myocardial infarction (AMI) that considered a broad range of clinical, demographic and age-related functional domains.

Methods: We used data from ComprehenSIVe Evaluation of Risk in Older Adults with AMI (SILVER-AMI), a prospective cohort study that enrolled participants aged ≥75 years with AMI from 94 US hospitals. Participants underwent an in-hospital assessment of functional impairments, including cognition, vision, hearing and mobility. Clinical variables previously shown to be associated with readmission risk were also evaluated. The outcome was 180-day readmission. From an initial list of 72 variables, we used backward selection and Bayesian model averaging to derive a risk model (N=2004) that was subsequently internally validated (N=1002).

Results: Of the 3006 SILVER-AMI participants discharged alive, mean age was 81.5 years, 44.4% were women and 10.5% were non-white. Within 180 days, 1222 participants (40.7%) were readmitted. The final risk model included 10 variables: history of chronic obstructive pulmonary disease, history of heart failure, initial heart rate, first diastolic blood pressure, ischaemic ECG changes, initial haemoglobin, ejection fraction, length of stay, self-reported health status and functional mobility. Model discrimination was moderate (0.68 derivation cohort, 0.65 validation cohort), with good calibration. The predicted readmission rate (derivation cohort) was 23.0% in the lowest quintile and 65.4% in the highest quintile.

Conclusions: Over 40% of participants in our sample experienced hospital readmission within 180 days of AMI. Our final readmission risk model included a broad range of characteristics, including functional mobility and self-reported health status, neither of which have been previously considered in 180-day risk models.

Keywords: acute coronary syndrome; epidemiology; health care; outcome assessment.

Figure 1

Risk model elements: 180-day readmission. After Bayesian model averaging with multivariable logistic regression, 10 variables were retained in the final risk model: these included comorbidities, presentation characteristics, self-reported health status and functional mobility. *Based on Short-Form 12 general health: excellent or very good (reference), good, fair and poor. †ECG changes: no ischaemic changes (reference), ST depression or T-wave inversion, ST elevation. ‡Timed Up and Go scores: ≤15 s (reference), >15–≤25 s, >25 s, unable to complete. §Ejection fraction categories ≥50 (reference), 40–<50, 30–<40 and <30. ¶Heart rate categories: <50 (reference), 50–69, 70–79, 80–89, 90–99, 100–109, 110–129, 130–149 and ≥150 bpm. #Diastolic blood pressure categories:<50 (reference), 50–59, 60–69, 70–79, 80–89, 90–99 and ≥100. COPD, chronic obstructive pulmonary disease.

Figure 2

Calibration of predicted versus observed probability of readmission at 180-days in the SILVER-AMI validation cohort, by quintile. Model calibration, validation cohort (by quintile). Shown are observed versus predicted 180-day readmission rates, by quintile, within the validation cohort. Error bars (red) represent 95% CIs. Among these quintiles, the SILVER-AMI readmission risk model was well calibrated (Hosmer-Lemeshow p > 0.05). SILVER-AMI, ComprehenSIVe Evaluation of Risk in Older Adults with AMI.