Selection bias in the management of unstable angina

To examine the criteria for selecting patients presenting with unstable angina for cardiac catheterisation and to assess the extent to which these criteria successfully incorporate high risk groups.

This was a prospective cohort study of 517 patients admitted 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 on 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 admission (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 rates 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).

Selection for early cardiac catheterisation in this unstable angina population was largely ischaemia-driven, based on ongoing chest pain and 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 first year.