Analytical approach:
A decision analytic model was developed to conduct the economic evaluation. For initial diagnosis a decision tree allocated patients to the appropriate diagnostic group; prognostic implications of being in one of these groups were then quantified using three distinct Markov models. The analysis used a lifetime horizon. The authors stated that the analysis was conducted from an NHS and Personal Social Services (PSS) perspective.
Effectiveness data:
The key effectiveness estimates were sensitivities and specificities of the diagnostic tools. Coronary angiography was assumed to have 100% sensitivity and specificity. All other diagnostic accuracy values were derived from the CE-MARC study. In the CE-MARC study all patients underwent ETT if physically able and were randomly scheduled for SPECT and CMR followed by coronary angiography irrespective of clinical intention. Other clinical inputs, such as mortality, severe stenosis and without stenosis but with angina were derived from the CE-MARC study, UK life tables, the EUROPA study, published literature and expert opinion.
Monetary benefit and utility valuations:
Utility estimates were based on the combination of several sources augmented by authors' assumptions to derive HRQoL weights by age, gender, baseline Canadian Cardiovascular Society classification and treatment status (whether the patient had received a revascularisation procedure or medical management). It was assumed that health-related quality of life (HRQoL) reductions for patients who experienced angina were a fixed proportion of the HRQoL of the general population by age.
Measure of benefit:
The health benefit was measured in quality-adjusted life-years (QALYs). Future benefits were discounted at an annual rate of 3.5%.
Cost data:
Direct costs to the NHS and PSS were included in the analysis. Cost categories included testing costs, revascularisation procedure costs, general treatment costs, fatal and non-fatal cardiovascular events and fatal non-cardiovascular events. Costs were derived from NHS Reference costs (2010-2011), a NICE document, Personal Social Services Research Unit costs and the EUROPA trial. For patients without significant stenosis or angina only the initial testing costs were included. Costs were expressed in 2010-2011 UK pounds sterling (£). Future costs were discounted at an annual rate of 3.5%.
Analysis of uncertainty:
Probabilistic sensitivity analysis was conducted to assess the impact of joint parameter uncertainty on the model results. The probability that each strategy was cost-effective across a range of willingness to pay thresholds (for an additional QALY) was calculated. A range of alternative scenarios for age, gender, Canadian Cardiovascular Society grade, prior likelihood of disease, quality of life decrements and costs of the diagnostic tests were considered.