A major factor contributing to spiralling health care costs is the proliferation of expensive new medical technology for diagnosis and treatment. These new technologies must be critically evaluated by well designed outcome based research to enable rational decisions to be made about their role in health care.
Australian Prescriber has previously featured articles on CT scanning and magnetic resonance imaging. This issue considers the use of thallium scanning, a useful but expensive diagnostic test for imaging myocardial perfusion, and a future issue will describe the very expensive positron emission tomography (PET) used in cardiology and neurology. While the diagnostic accuracy of these technologies is reasonably well defined, their role in contributing to better health outcomes is not.
The introduction of PET scanning into Australia has been carefully regulated; only two centres have been established and the utility of the technology is being critically evaluated. For example, in cardiology, the principal role of PET will be to identify patients with viable but noncontractile myocardium which may benefit from revascularisation. Studies will focus on the short and long term outcomes of diagnostic and management strategies involving both thallium and PET scanning. The benefits which may accompany these strategies will be defined, together with the costs to the patient and the health care system.
The technology of thallium scanning has improved progressively over the 15 years it has been available. There have been many studies of the utility and diagnostic accuracy of thallium scanning in several clinical situations (see Table 1, page 60). However, there have been few well designed studies of its utility as one part of a rational diagnostic and management strategy for patients with various manifestations of coronary disease.
Preoperative dipyridamole thallium scanning is said to identify patients at a high risk of cardiac complications during major vascular surgery. Based on the findings of earlier studies, preoperative thallium scanning has become routine in many centres. However, two recent well designed studies1,2 cast serious doubt on the predictive value of these routine scans. The most recent study2 included 457 consecutive patients undergoing elective abdominal aortic surgery. This study used the most modern methods of thallium scanning, but only age and definite evidence of coronary disease were identified as statistically significant predictors of postoperative cardiac adverse events.
The same arguments can be used with regard to many other widely accepted uses of thallium scanning. For example, thallium scanning can be used for risk stratification after myocardial infarction to identify those patients with an increased risk of further adverse events3, but should it be used? We do not know the answer to this question. My personal view is that it should not be used routinely for an indication where there are no data to show a clear cut improvement in outcome.
There is more than a 20-fold variation in the rate of thallium scanning per head of population between Australian states, and thallium scanning is not widely used in New Zealand. Is there any evidence that cardiovascular health is improved in those regions where more scans are done? The data on total mortality, cardiovascular mortality, incidence of myocardial infarction and mortality from myocardial infarction suggest there is no advantage. Thallium scanning is expensive. The Schedule fee for stress and redistribution imaging, together with ECG monitoring during exercise, amounts to just over $700. Using SPECT (see page 57) brings the total up to $880. Are we getting value for money?
In future, limited health care resources will require all new investigations to be evaluated thoroughly before they become an accepted part of practice.
- Mangano DT, London MJ, Tubau JF, Browner WS, Hollenberg M, Krupski W, et al. Dipyridamole thallium201 scintigraphy as a preoperative screening test: a reexamination of its predictive potential. Circulation 1991;84:493-502.
- Baron JF, Mundler O, Bertrand M, Vicaut E, Barre E, Godet G, et al. Dipyridamolethallium scintigraphy and gated radionuclide angiography to assess cardiac risk before abdominal aortic surgery. N Engl J Med 1994;330:663-9.
- Brown KA. Prognostic value of thallium201 myocardial perfusion imaging: a diagnostic tool comes of age. Circulation 1991;83:363-81.