Combined functional and anatomical imaging for the detection and guiding the therapy of coronary artery disease.

Cardiac imaging is used to confirm the diagnosis of coronary artery disease (CAD), to document ischaemia in patients with stable symptoms, to risk stratify patients, and to help choose treatment options and evaluate their efficacy. In the classic diagnostic path, the pre-test probability of CAD is estimated based on symptoms, sex, risk factors, biomarkers, and, when available, the result of exercise electrocardiography (ECG). Non-invasive imaging tests are recommended for patients with an intermediate probability (15–85%) of obstructive CAD, while symptomatic patients with a high probability (.85%) can undergo direct invasive examination (Figure 1A). On many occasions the choice of the non-invasive imaging method is based on local expertise and availability of the test. In this path, the final diagnosis and the decision about the revascularization method and the vessels treated are often determined using invasive coronary angiography (ICA). The role of non-invasive tests is mainly to select whether the patients need invasive testing. Coronary computed tomography angiography (CTA) has become an established non-invasive method for anatomic detection of CAD. Current techniques allow robust assessment of coronary atherosclerosis with acceptable radiation dose. Multicentre studies have demonstrated high diagnostic accuracy of CTA for the identification of .50% coronary artery stenoses, and most studies have shown a particularly high negative predictive value (NPV), making CTA an excellent tool for exclusion of CAD especially in symptomatic patients with a lower range of intermediate pre-test probability of CAD. The angiographic severity of a coronary lesion (detected either invasively or non-invasively) is a poor predictor of its haemodynamic significance. As expected, only a proportion of stenoses in CTA are associated with myocardial ischaemia. In stable CAD, the target of revascularization therapy is myocardial ischaemia, not the epicardial coronary disease itself. Revascularization procedures performed in patients with documented ischaemia reduce total mortality through reduction in ischaemic burden. Thus, functional assessment, non-invasiveor invasive, is essential for intermediate stenoses. Interrogation of both coronary anatomy and function is important in order to offer the most appropriate treatment strategy in patients with stable CAD. Non-invasive imaging can provide information on both of these, even in the same imaging session using hybrid imaging. Recently, several studies have combined evaluation of anatomy with CTA and perfusion imaging using either single photon emission tomography (SPECT) or positron emission tomography (PET). These studies have consistently shown improved diagnostic accuracy of combined or hybrid imaging as compared with the single techniques. Furthermore, vessel-specific functional information allowing targeted revascularization strategies can be obtained. Recently, it was also shown that combining anatomy and function added independent prognostic information. Groothuis et al. have now investigated the combined use of CTA and cardiac magnetic resonance imaging (CMR) for the diagnostic evaluation of patients with suspected coronary artery disease (CAD). The authors enrolled 192 patients with low or intermediate pre-test probability of CAD. The patients with obstructive CAD on CTA and/or myocardial ischaemia on CMR were referred for ICA. In addition to anatomical assessment in ICA, functional evaluation of intermediate lesions (30–70% diameter stenosis) with the use of fractional flow reserve (FFR) was planned as the reference method. The combination of CTA and CMR significantly improved specificity and overall accuracy (91%) for the detection of significant CAD as compared with stand-alone CTA or CMR. The results are in good agreement with previous data published on combined anatomical and functional imaging for the detection of CAD. The combination of CMR with CTA has also been studied previoulsy, but the study of Groothuis et al. included a larger population. In addition to perfusion, CMR can provide useful information