Due to rising healthcare costs, appropriate use of cardiovascular imaging is increasingly
emphasized by professional societies, third party payers and accreditation agencies
6],7],13],14]. To the best of our knowledge this is the first study to systematically and prospectively
assess the downstream utilization of angiography and revascularization procedures
based on the AUC for stress-CMR. We have shown that tests categorized by the AUC as
rarely appropriate, infrequently demonstrate ischemia, but the rates of downstream
cardiac catheterization were not significantly different to those categorized as appropriate
or maybe appropriate. Importantly when patients underwent cardiac catheterization
none of the rarely appropriate group went on to require subsequent revascularization.
These findings appear to support the current AUC classification of rarely appropriate
stress-CMR studies, since this group appears to result in suboptimal resource utilization.
In our study population, the great majority of tests ordered were deemed as appropriate
or maybe appropriate. Only, approximately 14% of the stress-CMRs were categorized
as rarely appropriate. This is similar to the inappropriate proportions reported for
stress echocardiography (9–33%) 15],16], Single Photon Emission Computed Tomography (SPECT) (7–46%) 17]–19], and Positron Emission Tomography (PET) (10.2%) 20]. It is interesting to speculate whether growing pre-certification demands by third-party
payers may have affected physicians test orderings patterns, but this cannot be assessed
from this study.
We found that studies that were classified as maybe appropriate had similar rates
of ischemia and led to similar rates of downstream catheterization and revascularization
as those that were deemed appropriate. This suggests that consideration could be given
to upgrading some of the common maybe appropriate indications to the appropriate category
(Table 2).
It is interesting to note that even when ischemia was reported, patients were more
likely to be referred for cardiac catheterization in the appropriate and maybe appropriate
groups. In fact none of the patients with ischemia in the rarely appropriate group
were referred for cardiac catheterization. The reasons for this are unclear but may
relate to physician’s assessment that invasive testing and revascularization would
not significantly change outcomes or symptoms in this patient group.
In this study we have looked at the rates of abnormal stress tests and the endpoints
of downstream angiography and revascularization to help assess optimal test-patient
selection and imaging utilization. However, there are a number of important caveats
to bear in mind. Higher rates of abnormal findings and greater use of angiography
or revascularization doesn’t necessarily imply better outcomes. Such validation would
require performance of prospective randomized outcome trials. Ideally these studies
should be part of larger initiatives to compare the effectiveness of different imaging
modalities. Although, such studies will be challenging to perform and fund, they are
of critical importance in clarifying optimal imaging strategies. Another important
point to emphasize is that stress testing can be very useful in patient management
even when it does not lead to angiography or revascularization 21]. For example a normal study may lead to exclusion of coronary artery disease as a
cause of symptoms, as well as to clinic/hospital discharge; or it may lead to ‘surgical
clearance’ in patients referred prior to elective non-cardiac surgery. Further studies
are required to more comprehensively assess these types of clinical impact and management
change 22],23].
Future steps in assessing and validating AUC for stress-CMR should aim to compare
the prognostic ability of the test across the various AUC categories. Such an approach
was recently undertaken by Doukky et al. in a large nuclear study 19]. They demonstrated that inappropriate use of SPECT was associated with reduced prognostic
value. In those patients whose scans were appropriate or uncertain, abnormal scans
were of significant value in predicting major adverse cardiac events (hazard ratio
3.1–3.7) compared with normal scans. However, in those with inappropriate scans, abnormal
studies did not achieve significance in predicting adverse cardiac events. Moreover,
all abnormal SPECT findings were associated with increasing rates of revascularization,
irrespective of the level of appropriateness.
Limitations
Our study was limited by a small sample size (?=?300) drawn from a single academic institution and may not be representative of
the wider population. However, this may have the advantage of providing uniform scanning,
interpretation and follow-up protocols. Larger studies with greater statistical power
and more events (particularly revascularization) will allow a more comprehensive analysis
of subgroups. The results of this study should therefore be regarded as preliminary,
until larger multicenter studies are completed. As mentioned above, cardiac catheterization
and revascularization are only part of the downstream clinical consequences of CMR-stress.
Cost-effectiveness was not assessed in this study and clearly needs to be the subject
of future studies aiming to establish the validity of the AUC.