Single photon emission computed tomography (spect) with technetium-99m (Tc-99m) sestamibi myocardial perfusion imaging is widely used because of its higher energy and reduced susceptibility to tissue attenuation. Adenosine stress is useful in older subjects who do not exercise well. Thus, the group from Cedars-Sinai Medical Center in Los Angeles sought to assess the value of adenosine stress SPECT sestamibi for the detection of severe coronary artery disease (CAD) in 130 women who also underwent coronary angiography. Those with prior revascularization and contraindications to adenosine were excluded (asthma, hypotension). Occlusion of the left main of more than 90% proximal left anterior descending; of more than 90% in two vessels; or of more than 70% in three vessels was present in 54. The remaining 76 women had no or mild-to-moderate CAD. Multivariate logistic regression analysis of clinical and perfusion imaging characteristics identified prescan likelihood of CAD and summed stress perfusion score as the only independent predictors of severe CAD. The probability of severe CAD increased with the summed stress score such that the point of maximum sensitivity and specificity was 80% at a stress score of 13. Stress scores above 8 had a sensitivity of 91% and a specificity of 70%. Cost analysis of various applications of angiography and perfusion scanning showed a range of cost per patient from $2800 to $2190 for angiography in all, to angiography only in those with a stress score of more than 8. Amanullah and colleagues conclude that adenosine stress SPECT sestamibi is a useful tool for the evaluation of CAD in women. (Amanullah AM, et al. Am J Cardiol 1997;80:132-137.)
COMMENT BY MICHAEL H. CRAWFORD, MD
It is useful to be able to identify high-risk CAD patients because they are more likely to benefit from revascularization. Clearly, adenosine SPECT sestamibi does this with a sensitivity of 91% at summed stress scores higher than 8. Summed stress scores are based upon a 20-segment myocardial model, and the degree of perfusion noted in each (higher numbers represent less perfusion). This may sound good to a radiologist or nuclear cardiologist with little or no direct patient care responsibilities, but the 70% specificity is a problem for the clinician. This means a 30% false-positive ratewomen with no-to-moderate disease who are potential candidates for conservative therapy being sent to angiography. This is undoubtedly why the direct cost analysis is so unimpressive$610 per patient difference between angiography for all and a selective approach using a stress score cut-off of 8. Also, you have the problem that 9% of the women with severe CAD are not properly identified (false-negatives). Based upon these data, angiography looks good.
Amanullah et al counter that true cost will be even higher if angiography is done in all since more will be revascularized. Perhaps, but revascularization may prevent future admissions for events that would otherwise increase the cost of the conservative approach over time. Unless true costs (direct and indirect) are evaluated, such comments are biased speculation. Amanullah et al further argue that their previous study showed that stress scores higher than 8 in women identified a high risk of subsequent death and myocardial infarction, suggesting that false-positive patients for severe CAD may still be at high risk of events and deserve angiography. Of course, this assumes that revascularization of women with mild- to-moderate CAD and a scan score higher than 8 will prevent future coronary events, which to my knowledge, has not been proven.
On the other hand, a scan score of less than 8 confers a good risk and would be reassuring if angiography was not done. The real problem is the poor specificity of a positive scan. This poor specificity is surprising since the high energy of Tc-99m sestamibi is supposed to reduce breast artifacts and other tissue attenuation problems that often lead to false-positive scans in women. In my experience, Tc-99m sestamibi SPECT has made the specificity problem in women worse than that observed in the old planar thallium days. Perhaps the more routine use of prone imaging in addition to supine imaging, three- headed cameras, or other technologic improvements will reduce this problem. For now, a strong argument can be made for proceeding directly to angiography in women with chest pain syndromes and moderate-to-high likelihood of CAD on clinical grounds.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content