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Debate: CT vs CMR as gatekeepers in suspected CAD

Debate CT vs CMR

Pro Coronary CT – Koen Nieman, Rotterdam, NL
Contra CMR – John Greenwood, Leeds UK

The debate was centered on the advantages and disadvantages of using cardiac Computed Tomography (CCT), as compared with stress imaging modalities such as Cardiac Magnetic Resonance (CMR), in the diagnostic and prognostic evaluation of patients with suspected Coronary Artery Disease (CAD). Dr. Nieman from Rotterdam, defending the CCT approach, underlined that CCT is already included in the current ESC Guidelines on Stable CAD  and is recommended as a possible first test in patients with intermediate-low pre-test probability of disease (PTP 15%-50%) or after stress imaging with uncertain results. Prospective, multicenter, multivendor studies using older 64 slices CT scanners, had shown that CT was a reliable tool for ruling out significant CAD in patients with suspected CAD even if the specificity was limited (64%), due to possible overestimation of the severity of a stenosis mainly in the presenceof calcified lesions, and the radiation exposure relatively high. In later studies which used more advanced scanners and low dose prospective ECG-gated CT angiography, the average effective dose was much lower (< 3 mSv) and the performance of CT as compared with ICA was definitely better with a sensitivity close to 100%  and specificity higher than 80%.  Dr. Nieman showed further evolution of CT technology so that at present a CCT scan can be performed with less than 1 mSv of effective dose and very high image quality. More recently cardiac imaging research was more focused on the impact on patients management and outcome. In the recently published PROMISE trial, 10,003 patients with stable angina and no known CAD were randomized either to a CT guided or a stress imaging guided diagnostic strategy and followed up for 2 yrs. The two groups had a low event rate (3.3 and 3.0 % at 2 yrs) with no difference in outcome. Nevertheless patients submitted to CT had lower proportion of normal findings at ICA and higher number of revascularizations with a slightly higher radiation exposure as compared with patients submitted to stress imaging. Dr Nieman also reported the results of the very recent CRESCENT trial performed in a population of patients (350) enrolled in 4 Dutch centers and randomized 2:1 to CT or stress imaging. The tiered cardiac CT protocol included a calcium scan followed by CT angiography if the Agatston calcium score was between 1 and 400. By 1 year, fewer patients randomized to cardiac CT reported anginal complaints and event-free survival was higher  than  for patients randomized to functional testing. In favour of the CT strategy, the final diagnosis was established sooner and additional downstream testing was required less frequently resulting in lower cumulative diagnostic costs. Dr Nieman concluded that for patients with suspected stable CAD, a tiered cardiac CT protocol incorporating the calcium scan offers an effective and safe alternative to functional testing  lowering diagnostic expenses and radiation exposure. He also underlined that the on going developments in CT technology could soon allow to answer to one of the major criticism to the CT guided approach which  is the lack of information on the functional significance of an anatomic coronary lesions. In fact CT perfusion is a promising approach towards a one stop-shop for anatomo-functional evaluation of suspected CAD by CT and CTA-FFR might provide in the next future a further hemodynamic evaluation of the significance of a coronary lesion on a totally non-invasive basis.

Dr Greenwood focused on some limitations of the CT guided approach advocating the preferential use of stress imaging (and of CMR among these modalities) in the screening of patients with suspected CAD. Coming back to ESC Guidelines on stable CAD he underlined the relevant role that is attributed to risk stratifications of patients with stable symptoms before possibly undergoing ICA and revascularization. In this context the presence of a large (>10%) inducible myocardial ischemia is considered the major determinant of high risk indicating further invasive assessment and possible revascularization. So, since CCT does not provide yet a functional information on the coronary lesions, a stress imaging could be better as first or complementary test to stratify risk and indicating further procedures in patients with suspected CAD. Dr. Greenwood underlined as the evaluation of a technique to be valuable and appropriate for a specific clinical question should rely upon three different capabilities: 1. Clinical efficacy (diagnostic performance); 2. Cost-Effectiveness; 3. Prognostic stratification and improvement of outcome. These three requirements are respected for CMR as some Dr. Greenwood’s studies document such as the original CE-MARC trial (and further analysis) documenting diagnostic accuracy, cost-effectiveness and capability to improve outcome of CMR in patients with stable CAD. Dr. Greenwood finally underscored that CT would not replace ICA and that radiation exposure could be still a risk whether appropriate methodology is not utilized.

The debate went on after the two presentations and was summarized by the two chairmen  by the recognition that both CCT and CMR are valid tools in patients with suspected CAD. Dr. Neglia from Pisa underscored that CCT should be  at present preferentially used to rule out obstructive disease in patients with lower risk and intermediate-low pre-test probability of disease. CCT has also the capability to describe the individual atherosclerotic burden which is per se a prognostic indicator requiring appropriate medical treatment. All agreed that stress imaging including CMR has a relevant role in selecting candidates to invasive procedures. Dr. Schwitter from Lousanne underscored  that efforts to minimize the radiation exposure are warranted.  

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.