Defining the appropriate CTA stenosis threshold for gatekeeping to invasive angiography: 50% or 70%?

There is currently much debate around the limited positive predictive value (PPV) of CT coronary angiography (CTA). There remain no published studies comparing different thresholds to define significant visual stenoses on CTA compared to the gold standard quantitative coronary angiography (QCA). The spatial resolution for ICA is (0.1 mm)(3) compared with (0.5 mm)(3) in clinical CTA and direct comparison introduces a systematic overestimation of stenosis severity by CTCA. Assessing both ≥ 50% and ≥ 70% visual stenoses on CTA with QCA we found that the negative predictive value (NPV) of CTA is equally high for both. The PPV of CTA improves using ≥ 70% but with a loss of sensitivity. Using ≥ 70% stenosis on CTA for referral for ICA would reduce the number of ICA that does not lead to percutaneous intervention (PCI) but a functional test for intermediate lesions (visual stenoses of 50%-69%) on CTA is recommended to overcome the reduction in sensitivity.