Methods: A probabilistic model was constructed to estimate costs and quality-adjusted life years (QALYs) of an early interventional strategy (routine angiography followed by revascularization) and a conservative strategy (ischemia-driven or symptom-driven angiography). A short-term decision tree was used to model costs and events during the acute hospitalization and a Markov structure was employed for the long-term decision model. Using individual-patient data from the Randomized Intervention Trial of unstable Angina (RITA-3), which followed 1810 patients for 5 years, the probability of a combined event of non-fatal myocardial infarction or death from cardiovascular causes during the acute hospitalization was estimated using logistic regression. A Weibull regression was used to estimate the rate of the combined event over the remainder of the clinical trial. Estimated parameters from the Weibull regression, adjusted for age, were used to extrapolate event rates from the end of the clinical trial. A pooled relative treatment effect for the combined event was estimated from a random effects meta-analysis of 7 trials in this patient population. Heterogeneity in baseline events rates, costs and utilities was explicitly modelled using covariates such as age, gender and several clinical risk factors, and cost-effectiveness was estimated for patients with different characteristics.
Results: The incremental cost per QALY of an early interventional strategy compared with a conservative strategy was well below generally accepted cost-effectiveness thresholds for all analysed subgroups (ranging from 8,000 to 16,000 pounds sterling). The results of the probabilistic analysis indicated that the probability of an early interventional strategy being cost-effective was over 80 % for all analysed subgroups employing a cost-effectiveness threshold of 30,000 pounds per QALY.
Conclusions: An early interventional strategy in patients presenting with NSTE-ACS has incremental costs per QALY gained below conventional thresholds. Patients with low baseline risk gain less from an early interventional strategy in the short term but have longer life expectancy to utilise this initial gain whereas the opposite is the case for patients with high baseline risk.