Invasive coronary angiography is problematic – specifically, it’s invasive. Radial artery approaches have reduced the incidence of bleeding complications, but it remains a costly and non-risk-free procedure. In lieu of ICA, CT coronary angiography has become increasingly popular. However, CCTA is problematic – specifically, it’s inaccurate.
A few years ago, DeFACTO was published in JAMA and covered on this blog, a study evaluating a non-invasive model of fractional flow reserve added on to CCTA in an attempt to improve accuracy at identifying true culprit lesions. DeFACTO was negative – specifically, the per-vessel performance at predicting flow-limiting lesions compared to the traditional 50% stenosis cut-off of CCTA was nearly identical.
Two years have passed, however, and we have a new study – NXT – using the next iteration of the HeartFlow software, and, of course, performed by authors with robust conflicts-of-interest. Now, improvements in image quality and luminal modeling – as well as refined exclusion criteria to prevent troublesome images confounding their software – have improved performance to the point where, yes, it now seems to out-perform baseline CCTA.
The catch, of course, is the CCTA criterion standard is abysmal. Compared with the ACRIN-PA or ROMICAT studies with their pro-CCTA COI, in which CCTA is the best thing since sliced bread, these folks are unconcerned with the collateral damage of degrading CCTA. In this study, as performed on patients with suspected CAD, of 237 vessels read as “positive” by CCTA (>50% stenosis), only 83 (35.0%) were actually judged to be flow-limiting lesions on ICA – which is to say, false positives doubled the true positives. Likewise – in contrast to the ROMICAT and ACRIN studies purveying CCTA as a bulletproof mechanism for discharge – 17 of 247 (6.8%) patients read as negative by CCTA (<50% stenosis) actually had flow-limiting disease.
False positives more two-thirds of the time? And then a 7% miss rate of clinically important stenosis? Basic, anatomic CCTA as previously described – not as fantastic as you’ve been led to believe.
The HeartFlow software? Perhaps. Effectiveness evaluations absent pervasive COI will be necessary to truly describe its value.
“Diagnostic Performance of Noninvasive Fractional Flow Reserve Derived From Coronary Computed Tomography Angiography in Suspected Coronary Artery Disease”
http://www.ncbi.nlm.nih.gov/pubmed/24486266