One of the arguments against CCTA is that it only describes coronary anatomy – and has no demonstrated clinical predictive value regarding whether the observed lesions are flow-limiting or potentially related to anginal symptoms. This study develops a computational fluid dynamics model that attempts to predict flow through coronary stenoses seen on CCTA.
Korea, Latvia, and California come together to evaluate 103 patients in a multicenter trial in which patients with suspected CAD underwent CCTA, invasive coronary angiography, and fractional flow reserve measurement. They used only 256 and 64-slice scanners for CCTA, and CAD was quantified as none, mild (0-49%), moderate (50-70%), and severe (>70%). Patients then underwent invasive coronary angiography where ischemia-related flow-limitation was defined as a fractional flow reserve of < 0.80. The study group then developed a method of deriving the FFR from CCTA data, and compared it to the actual measurements from invasive coronary angiography using the same threshold value.
The conclusions from this article depend what takeaways you’re looking for. On one hand, the FFR-CT method was pretty decent – 87.9% sensitive and 82.2% specific regarding their definition of ischemia-causing lesions. The other real takeaway is that CCTA has abysmal performance at the threshold typically used in the CCTA studies of >50% stenosis. Their calculated +LR for CCTA stenoses >50% was only 1.51 in the setting of a specificity of 39.6%. To me, another nail in the coffin showing CCTA is the d-Dimer of CAD, leading to a ton of unnecessary testing.
Considering it took them 5(!) hours to generate the FFR-CT measurement based on Newtonian fluid and Navier-Stokes equations on a parallel supercomputer, I don’t think we’ll be seeing this anytime soon – but hope is out there for the future.
“Cardiac Imaging Diagnosis of Ischemia-Causing Coronary Stenoses by Noninvasive Fractional Flow Reserve Computed From Coronary Computed Tomographic Angiograms”
http://www.theheart.org/article/1299631.do