Predicting 6-Month Mortality for Older Adults Hospitalized With Acute Myocardial Infarction: A Cohort Study

Abstract

Background: Older adults with acute myocardial infarction (AMI) have higher prevalence of functional impairments, including deficits in cognition, strength, and sensory domains, than their younger counterparts.

Objective: To develop and evaluate the prognostic utility of a risk model for 6-month post-AMI mortality in older adults that incorporates information about functional impairments.

Design: Prospective cohort study. (ClinicalTrials.gov: NCT01755052).

Setting: 94 hospitals throughout the United States.

Participants: 3006 persons aged 75 years or older who were hospitalized with AMI and discharged alive.

Measurements: Functional impairments were assessed during hospitalization via direct measurement (cognition, mobility, muscle strength) or self-report (vision, hearing). Clinical variables associated with mortality in prior risk models were ascertained by chart review. Seventy-two candidate variables were selected for inclusion, and backward selection and Bayesian model averaging were used to derive (n = 2004 participants) and validate (n = 1002 participants) a model for 6-month mortality.

Results: Participants' mean age was 81.5 years, 44.4% were women, and 10.5% were nonwhite. There were 266 deaths (8.8%) within 6 months. The final risk model included 15 variables, 4 of which were not included in prior risk models: hearing impairment, mobility impairment, weight loss, and lower patient-reported health status. The model was well calibrated (Hosmer-Lemeshow P > 0.05) and showed good discrimination (area under the curve for the validation cohort = 0.84). Adding functional impairments significantly improved model performance, as evidenced by category-free net reclassification improvement indices of 0.21 (P = 0.008) for hearing impairment and 0.26 (P < 0.001) for mobility impairment.

Limitation: The model was not externally validated.

Conclusion: A newly developed model for 6-month post-AMI mortality in older adults was well calibrated and had good discriminatory ability. This model may be useful in decision making at hospital discharge.

Primary funding source: National Heart, Lung, and Blood Institute of the National Institutes of Health.

Figure 1.

Receiver-operating characteristic curves for the SILVER-AMI and GRACE mortality risk models. In our validation cohort, we compared the AUCs for the SILVER-AMI 6-month mortality risk model and the GRACE risk model (which was previously developed for post-AMI 6-month mortality). The GRACE risk model includes the following factors: age, development (or history) of heart failure, peripheral vascular disease, systolic blood pressure, Killip class, initial serum creatinine concentration, elevated initial cardiac markers, cardiac arrest on admission, and ST-segment deviation. The diagonal green line indicates 50% discrimination and is provided to show how much each model improves on purely random assignment of risk. As shown, the SILVER-AMI mortality risk model showed superior discrimination compared with the GRACE model (AUC = 0.84 vs. 0.76; P < 0.001). AMI = acute myocardial infarction; AUC = area under the curve; GRACE = Global Registry of Acute Coronary Events; SILVER-AMI = Comprehensive Evaluation of Risk in Older Adults with AMI.

Figure 2.

Calibration plot for the SILVER-AMI mortality risk model. Shown are deciles of observed 6-month risk versus predicted 6-month mortality, with the GRACE model applied to the SILVER-AMI validation cohort (top) and the SILVER-AMI model applied to the SILVER-AMI validation cohort (bottom). Error bars represent 95% CIs. AMI = acute myocardial infarction; GRACE = Global Registry of Acute Coronary Events; SILVER-AMI = Comprehensive Evaluation of Risk in Older Adults with AMI.