CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Joanne D. Schuijf, MSc and
Jeroen J. Bax, MD, PhD*
* Department of Cardiology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, the Netherlands (Email: jbax{at}knoware.nl).
We thank Drs. Spevack and Levsky for their interest in our article on the relationship between multislice computed tomography (MSCT) coronary angiography and myocardial perfusion imaging (MPI) (1).
In our study, MSCT and MPI were compared in patients with an intermediate pretest likelihood. In the majority of patients with normal MSCT (no atherosclerosis), MPI was normal as well. However, in patients with significant lesions on MSCT, MPI results were abnormal in only 50%, indicating that MSCT can not predict abnormal perfusion/ischemia. Nonetheless, these observations also showed that the presence of substantial atherosclerosis, including significant stenoses, cannot be ruled out by MPI. Thus, the techniques may be considered to provide different information; whereas MPI provides information on the presence of ischemia, MSCT tells us whether atherosclerosis is present or not. Integration of both, therefore, may prove helpful in deciding the optimal treatment strategy.
The first concern that Drs. Spevack and Levsky raise is that our observations appear to be based on data showing poor efficacy for MPI. However, their argument is predominantly based on the findings of a subanalysis of our data, namely, the performance of MSCT and MPI in those patients referred for conventional coronary angiography. However, we recommend that those observations be treated with care, because they are hampered by the presence of referral bias, thus negatively influencing MPI results in particular. In our paper, therefore, those data are solely used to confirm that MSCT has a good diagnostic accuracy in patients at intermediate risk. Moreover, one needs to realize carefully that even obstructive atherosclerotic lesions do not necessarily result in ischemia. With the increasing awareness of the mismatch between ischemia (MPI) and atherosclerosis/stenosis (MSCT and invasive angiography), one may even question the use of lesions on angiography as the gold standard.
The second issue the authors raise concerns our statement that in patients with abnormal MPI revascularization may be indicated. We fully agree with the authors that clinical presentation also should always be considered when deciding the need for revascularization. Nevertheless, in contrast to the opinion of Drs. Spevack and Levsky, we feel that assessment of the presence and extent of ischemia are of paramount importance in the prediction of benefit from revascularization. Recently, Hachamovitch et al. (2) published their observations in 5,366 consecutive patients without earlier revascularization who received either medical therapy or revascularization after initial MPI. In line with previous studies (3), the authors demonstrated that survival benefit from revascularization is proportional to the extent of ischemia. Although left ventricular ejection fraction was found to predict cardiac death, only inducible ischemia identified which patients had a short-term benefit from revascularization.
However, we fully agree with Drs. Spevack and Levsky that despite normal MPI results long-term outcomes may differ between patients with either minor or severe coronary artery disease (CAD). Indeed, the identification of considerable CAD in patients with still normal MPI may become an important advantage of using MSCT coronary angiography in addition to MPI. To this purpose, sequential imaging strategies could potentially be beneficial. Unfortunately at present, available data are too scarce to support such algorithms. Indeed, we fully agree with the authors that further investigations addressing patient outcomes as well as cost-effectiveness are highly warranted.
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References
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1. Schuijf JD, Wijns W, Jukema JW, et al. Relationship between noninvasive coronary angiography with multi-slice computed tomography and myocardial perfusion imaging J Am Coll Cardiol 2006;48:2508-2514.[Abstract/Free Full Text]2. Hachamovitch R, Rozanski A, Hayes SW, et al. Predicting therapeutic benefit from myocardial revascularization procedures: are measurements of both resting left ventricular ejection fraction and stress-induced myocardial ischemia necessary? J Nucl Cardiol 2006;13:768-778.[CrossRef][Web of Science][Medline] 3. Hachamovitch R, Hayes SW, Friedman JD, et al. Comparison of the short-term survival benefit associated with revascularization compared with medical therapy in patients with no prior coronary artery disease undergoing stress myocardial perfusion single photon emission computed tomography Circulation 2003;107:2900-2927.[Abstract/Free Full Text]
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