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KCE Reports 82 Multislice CT in Coronary Heart Disease 85
DISCUSSION
The economic evaluation presented in this paragraph is limited to an application of
Belgian cost data to one RCT and extending the economic assessment presented by
Goldstein et al. to include health outcomes. The objective was modest, being to
challenge the conclusion drawn by Goldstein et al. and frequently cited about the costeffectiveness
of MSCT relative to standard of care. A full economic evaluation would
require evidence on the effectiveness of MSCT in real world in low- to intermediate
risk patients. Evidence on diagnostic accuracy in well-defined patient populations is being
built up, meanwhile leaving the assessment of the impact of MSCT on patient outcomes
unevaluated. An option is to model final outcomes such as life-years gained based on
evidence about the relationship between intermediate outcomes parameters (e.g.
detected CAD) and final outcome parameters (e.g. life-years gained). This means that
sufficient information must be available about the clinical significance of the CAD
detected by MSCT or its comparator in the target population. Unfortunately this
information is rarely available for patients at low- to intermediate risk for coronary
events, as most studies stop whenever CAD is diagnosed.
Our economic assessment, based on observed data from one RCT, showed that the
total costs of MSCT angiography in patients admitted to the emergency department
because of chest pain and deemed at low risk for future events are higher than that of
the standard of care, defined as 3 cardiac biomarker tests (at 0, 4 and 8 hours), 2 ECGs
and nuclear stress testing. The outcomes of the diagnostic strategy with MSCT as a
filter for nuclear stress testing, i.e. only patients with intermediate or inconclusive
MSCT test results undergo a nuclear stress test, are worse than the outcomes of the
standard of care strategy. Because more patients in the MSCT arm undergo
revascularisation, and revascularisation impacts on health-related quality of life, this
result is not surprising. If the observed trend in the RCT of more revascularisations in
the MSCT arm continues in longer follow-up periods, the difference between the costs
and outcomes of both diagnostic strategies will only increase. The RCT is, however,
underpowered to allow such hypothesis.
Goldstein et al. did not reach the same conclusion, mainly because they stopped their
costing procedure when the decision to do an invasive angiography was taken. 67 Their
endpoint, therefore, was an intermediate one. The relevance of it can be questioned, in
general but especially in this patient population. The general argument against the use of
intermediate endpoints in economic evaluation is that they are not relevant for the
policy maker or the patient. The policy maker is interested in how he can obtain the
highest health benefit at a given cost. The patient is interested in how he can obtain the
highest health benefit at reasonable out-of-pocket expenses. The fact of reaching more
or less quickly a decision to do a CCA is not relevant if eventually this has no impact on
final outcomes such as life years gained or quality-adjusted life years gained.
The results of our economic evaluation only pertain to the diagnostic and treatment
path followed by actual patients observed in the trial and to the period of observation in
the trial. The advantage of this approach is that no assumptions have to be made about
the future events and interventions, thereby reducing the uncertainty of the results. The
disadvantage of the approach, however, is that it also introduces a level of uncertainty in
the sense that it is uncertain to what extent the results would hold if larger patient
populations are treated. The patient numbers in each health state were too small to
reliably estimate transition probabilities and make the model more generic. For
instance, none of the patients in the “standard of care”-arm who underwent a late CCA
were revascularised. This might be a coincidence due to the small number of patients
undergoing a late CCA. The RCT was not powered to detect such potential relevant
differences. In real life, with very large patient numbers, the situation might be different,
and some patients might undergo revascularisation if late CCA is positive. To increase
the generalizability of the results, more data on the long term consequences of both
diagnostic interventions would be needed (need for revascularisation, AMI, death). Data
from larger data sets would allow us to define transition probabilities and hence built a
more generic model.