I have read the article published by the group at the Hospital Clínic de Barcelona1 with great interest, and would like to congratulate the authors publically on their outstanding research endeavor.
Nonetheless, although the authors recommend “a balanced strategy” combining both techniques, in my reading of the article I detect an underlying conflict between them, and would like to make some comments related to this. These comments are intended in no way to diminish the authors’ extraordinary work, but rather to present “the current value” of computed tomography (CT).
- 1.
A limitation not mentioned by the authors is the long time elapsed between the conduct of the study and its publication. It may be that the intervening 6 years have brought no changes in exercise echocardiography and that older results thus remain applicable in 2014; however, developments in multidetector computed tomography (MDCT) during this period have been truly spectacular and exponential. Besides improved spatial and temporal resolution and reduced radiation doses, these developments include the introduction of complementary explorations for the detection of ischemia (perfusion, noninvasive determination of functional repercussion of stenosis, etc.). These advances have made MDCT one of the most sensitive and specific methods for ruling out significant coronary artery disease, second only to invasive coronary angiography. The noninvasive nature of MDCT moreover brings added benefits, including the detection of subclinical coronary artery disease,2 the potential to characterize high-risk plaques, and prognostic value.
- 2.
Technical considerations. The diagnostic performance of MDCT could have been improved with an optimized spatial resolution of the reconstructions, achievable by modifying the slice thickness, the between-slice increase and filters as described by other authors3 working with exactly the same type of scanner. Additionally, given the mean body surface area observed in the study population (although the benchmark parameter in cardiac CT is body-mass index), a tube potential of 100kV would have improved luminal contrast in the coronary arteries, thereby facilitating image interpretation and exponentially reduces the radiation dose. Such dose reductions are line with Society of Cardiovascular Computed Tomography guidelines, which recommend the establishment of quality assurance procedures to meet the following objectives: sufficient diagnostic quality in ≥ 95% of scans, a demonstrable diagnostic accuracy at least 75% that of invasive coronary angiography, and a mean radiation dose at the reference level (12 mSv according to the most recent guidelines).4 Today, with a careful acquisition protocol and the latest scanners, doses are normally in the region of 1-2 mSv or even lower, well below the 7-10 mSv in invasive coronary angiography and the 8-10 mSv in isotope studies with gamma radiation, demonstrated to be more harmful than X rays.
- 3.
Methodological considerations. An Agatston score > 400 is not equivalent to the detection of significant coronary artery disease by MDCT because this threshold drags down the specificity of the method, with 20% of patients with this score having no disease.5 The authors’ statement in the Discussion that “MDCT has low diagnostic specificity” seems to me to be inappropriate. What limits specificity is setting the significance threshold at ≥ 50% when the “reference pattern” is ≥ 70% for invasive coronary angiography (luminogram) and MDCT is based on this same “luminogram”, with the advantage of assessing the coronary wall. The ≥ 50% significance threshold was established in the cited study by Hoffmann, in which final cost-effectiveness did not reach statistical significance. In contrast, the Goldstein study, using a significance threshold of ≥ 70%, showed a significantly positive cost-effectiveness for MDCT ($2137 for MDCT compared with $3458 for standard; P < .0001).
The major scientific societies now accept the diagnostic value of both techniques and their complementary nature, especially in non-diagnostic MDCT studies and studies that indirectly evaluate the functional repercussion of intermediate or limiting stenosis, an evaluation achieved directly with pressure guides in invasive coronary angiography.