Coronary CT angiography derived fractional flow reserve: Methodology and evaluation of a point of care algorithm

• We provide a methodological background of an on-site CTA-FFR application.
• Misalignment CT acquisition artifacts reduce CTA-FFR diagnostic performance.
• Left ventricle mass, diabetes, and vessels size increase deviation of CTA-FFR.
• Increasing CAC scores non-significantly reduce CTA-FFR diagnostic specificity.

BackgroundRecently several publications described the diagnostic value of coronary CT angiography (coronary CTA) derived fractional flow reserve (CTA-FFR). For a recently introduced on-site CTA-FFR application, detailed methodology and factors potentially affecting performance have not yet been described.ObjectiveTo provide a methodological background for an on-site CTA-FFR application and evaluate the effect of patient and acquisition characteristics.MethodsThe on-site CTA-FFR application utilized a reduced-order hybrid model applying pressure drop models within stenotic regions. In 116 patients and 203 vessels the diagnostic performance of CTA-FFR was investigated using invasive FFR measurements as a reference. The effect of several potentially relevant factors on CTA-FFR was investigated.Results90 vessels (44%) had a hemodynamically relevant stenosis according to invasive FFR (threshold ≤0.80). The overall vessel-based sensitivity, specificity and accuracy of CTA-FFR were 88% (CI 95%:79–94%), 65% (55–73%) and 75% (69–81%). The specificity was significantly lower in the presence of misalignment artifacts (25%, CI: 6–57%). A non-significant reduction in specificity from 74% (60–85%) to 48% (26–70%) was found for higher coronary artery calcium scores. Left ventricular mass, diabetes mellitus and large vessel size increased the discrepancy between invasive FFR and CTA-FFR values.ConclusionsOn-site calculation of CTA-FFR can identify hemodynamically significant CAD with an overall per-vessel accuracy of 75% in comparison to invasive FFR. The diagnostic performance of CTA-FFR is negatively affected by misalignment artifacts. CTA-FFR is potentially affected by left ventricular mass, diabetes mellitus and vessel size.