Non-invasive fractional flow reserve using computed tomographic angiography: where are we now and where are we going?

### Learning objectives Coronary computed tomographic angiography (CTA) is now established as a clinically valuable non-invasive anatomical test for the detection and exclusion of significant coronary disease. A number of prospective multicentre trials have shown coronary CTA to be an ideal test for the exclusion and detection of coronary disease using invasive angiography as the reference.1–3 Despite this, owing to its relatively low positive predictive value of 48% and inability to determine functional significance,1 its use in international guidelines has generally been restricted to patients with chest pain at a low-intermediate risk of having coronary artery disease (CAD).4 For patients at an intermediate risk of CAD, functional testing is generally indicated, and for high-risk patients, invasive coronary angiography (ICA) remains the recommended diagnostic test. Although this strategy is designed to determine whether a patient’s symptoms are attributable to CAD, and specifically myocardial ischaemia, recent studies indicate that this approach has important flaws. In a study of almost 400 000 patients, Patel et al showed that up to 62% of the patients who underwent ICA in the USA were subsequently found to have no significant obstructive disease. Furthermore, of those patients with a positive stress test, approximately two-thirds had no obstructive disease and, conversely, 28% of the patients with a negative stress …