AIMS: There is no mention in the current "appropriateness criteria for CTCA" of the need of CTCA investigation prior to an attempt at recanalisation of a CTO. To define better the role of CTCA in the treatment of patients with CTOs, we performed CTCA in a consecutive cohort of eligible patients who were scheduled for percutaneous recanalisation of a CTO.METHODS AND RESULTS: Symptomatic patients due to a CTO suitable for percutaneous treatment were included. One hundred and thirty-nine (142 CTOs) patients were studied. Overall success rate was 62.7%. By CTCA, the occlusion length was 24.9 +/- 18.3 vs. 30.7 +/- 20.7 mm in successful and failed cases (p = 0.1), but the frequency of patients with an occlusion length >15 mm was different, i.e., 63.2% vs. 82.7%, respectively (p = 0.02). Severe calcification, (> 50% CSA) was more prevalent in failed cases (54.7% vs. 35.9%, p = 0.03). Calcification at the entry of the occlusion was present in 58.5% of the failures vs. 41.6% of the successful cases (p = 0.04), while calcium at the exit was not different. The length of calcification was 8.5 +/- 8.4 vs. 5.5 +/- 6.6 mm in the failed and successful cases respectively (p = 0.027). By multivariable analysis, the only independent predictor of procedural success was the absence of severe calcification as defined by CTCA. The mean effective radiation dose of the PCI was 39.3 +/- 30.1 mSv. The mean effective radiation dose of CT scan was 22.4 mSv: 19.2 +/- 6.5 mSv for contrast-enhanced scan, 3.2 +/- 1.7 mSv for calcium scoring scan.CONCLUSIONS: More severe calcified patterns, as assessed by CTCA, are seen in failed cases. The radiation exposure during a CT scan prior to a CTO PCI is considerable, and further studies are required to determine whether this extra diagnostic study is warranted.