Among 2,001,529 PCI admissions in the NCDR database between January 1, 2004 and June 20, 2009 (), there were 1,040,889 patients discharged after PCI between 2004 and 2007, of whom 518,195 were age 65 or older. Of these 518,195 patients, successful linkage to the CMS database was accomplished in 343,496 (66%). The comparison of linked to unlinked data is available in an electronic appendix (Table e1
). Due to uncertainty about the date of death, 30 additional patients were excluded from the final dataset for analysis, resulting in a final study population of 343,466.
The 343,466 patients in the study population were randomly divided into a derivation cohort with 206,081 patients (60%) and a validation cohort with 137,385 patients (40%). Patient characteristics overall, in the STEMI and in the Without STEMI study populations of the derivation cohort are displayed in . Overall, these groups are representative of patients undergoing PCI with the exception that the study population was limited to those over age 65. The mean age of our study population was 75 years and the majority of patients were white. The mean BMI was within the overweight range, and just under half never smoked. Diabetes was present in a substantial minority, and the majority had hypertension. Prior revascularization was common. A history of heart failure was noted in a minority, and comorbidities were common. Mean ejection fraction was below 0.50 for STEMI patients, above 0.50 for Without STEMI. While multivessel disease was common, left main disease remained a small minority. Within the group Without STEMI, most cases were elective or urgent, while most cases of STEMI were emergent or salvage.
Patient Characteristics in the Derivation Cohort*
Median follow-up was 15 months from index procedure. Mortality is summarized in . Of the 206,081 patients in the derivation cohort, 22,012 died, of whom 4,526 were in the STEMI group and 17,486 in the Without STEMI group. Mortality at 3 years was 18.7% overall, 25.4% in the STEMI group and 17.7% in the group Without STEMI.
Multivariable predictors of mortality in the derivation study populations for STEMI and Without STEMI are shown in . The 30-day, 1-year and 2-year c indices in the validation dataset were 0.78, 0.79 and 0.79 for STEMI and 0.76, 0.78 and 0.78 for the Without STEMI models, respectively. The hazard ratios (HRs) and 95% confidence intervals (CIs) are shown for each group at less than 1 month, 1 to 12 months and greater than 12 months. In general, the 95% confidence intervals were relatively small due to the size of the study population. Many variables were predictive, although few had large hazard ratios. Predictive variables include demographics, co-morbidity, prior procedures, severity of illness, and urgency of presentation. Variables related to anatomical severity of disease, such as ejection fraction and left main disease, or to severity of disease at presentation, such as cardiogenic shock, were relatively powerful predictors of mortality. Some variables, such as age, had relatively constant hazard ratios across the time periods. Others, such as male sex, were initially neutral or associated with decreased risk, but showed increased risk over time. Some, such as prior valve surgery, were unstable due to low numbers of patients. Finally, variables associated with the acuteness of the presentation, such as cardiogenic shock, portended increased risk during the first month, but not long term.
Predictors of Survival in the Derivation Cohort
Calibration of the model in the validation population is presented in , with observed and predicted risk displayed across the spectrum of risk from under 5% to over 70% risk in STEMI (Panel A) and from approximately 2% to 40% in patients Without STEMI (Panel 2b). The observed and predicted risks were almost identical up to 20% predicted mortality; above this range mortality risks was underestimated to some extent.. Survival curves for both STEMI and Without STEMI groups in the validation population are displayed in , with slight under prediction of mortality in the STEMI patients (Panel 3A), and with observed and predicted curves being nearly identical for patients Without STEMI (Panel B). Note that there is significantly higher initial mortality with STEMI than Without STEMI, accounting for most of the difference in survival by 1000 days. Observed and predicted survival in subgroups of STEMI and Without STEMI in the validation population are displayed in and . There is a difference in survival for all subgroups except by sex. The observed and predicted survival rates are quite similar in subgroups with larger sample sizes, but varied somewhat from the predicted in STEMI subgroups with smaller sample sizes.
Predicted and observed mortality at 1 year in patients with ST elevation MI (STEMI) and without ST elevation myocardial infarction (Without STEMI).
Predicted and observed mortality over 3 years in patients with ST elevation MI (STEMI) and without ST elevation myocardial infarction (Without STEMI).
Predicted and observed mortality for subgroups over 3 years in patients with ST elevation MI (STEMI).
Predicted and observed mortality for subgroups over 3 years in patients without ST elevation myocardial infarction (Without STEMI).