Selection bias in the management of unstable angina

Objectives: To examine the criteria for selecting patients presenting with unstable angina for cardiac catheterisation and to assess the extent to whi ch these criteria successfully incorporate high risk groups. Methods and results: This was a prospective cohort study of 517 patients ad mitted with unstable angina with 12 months follow-up; 139 patients (26.9%) had cardiac catheterisation 32 days or longer after presentation. The odds of early catheterisation were increased by regional ST segment depression o n the presenting ECG (odds ratio (OR) 1.70, 95% confidence intervals (CI) 1 .01-2.87) and ongoing ischaemic chest pain more than 12 hours after admissi on (OR 9.72, CI 6.10-15.49), and reduced by age over 65 years (OR 0.56, 95% CI 0.35-0.90) and heart failure (OR 0.26, CI 0.11-0.64). The 12-month rate s of myocardial infarction (MI) or death were 8.6% and 17.7% (p = 0.01) in patients who were and were not referred for early cardiac catheterisation, respectively. Survival analysis showed that the odds of MI and death in the first 12 months were increased substantially by heart failure (OR 2.82, 95 % CI 1.53-5.20) and age over 65 (OR 1.91, 95% CI 1.13-3.23). Conclusion: Selection for early cardiac catheterisation in this unstable an gina population was largely ischaemia-driven, based on ongoing chest pain a nd ST segment depression. This policy was associated with a low event rate in the ischaemic group, but it failed to target elderly patients and those with heart failure who were at greatest risk of MI and death during the fir st year.