Characterization of functionally significant coronary artery disease by a coronary computed tomography angiography-based index: a comparison with positron emission tomography

Aims To test the hypothesis that virtual functional assessment index (vFAI) is related with regional flow parameters derived by quantitative positron emission tomography (PET) and can be used to assess abnormal vasodilating capability in coronary vessels with stenotic lesions at coronary computed tomography angiography (CCTA). Methods and results vFAI, stress myocardial blood flow (MBF), and myocardial flow reserve (MFR) were assessed in 78 patients (mean age 62.2 ± 7.7 years) with intermediate pre-test likelihood of coronary artery disease (CAD). Coronary stenoses ≥50% were considered angiographically significant. PET was considered positive for significant CAD, when more than one contiguous segments showed stress MBF ≤2.3 mL/g/min for ¹⁵O-water or <1.79 mL/g/min for ¹³N-ammonia. MFR thresholds were ≤2.5 and ≤2.0, respectively. vFAI was lower in vessels with abnormal stress MBF (0.76 ± 0.10 vs. 0.89 ± 0.07, P < 0.001) or MFR (0.80 ± 0.10 vs. 0.89 ± 0.07, P < 0.001). vFAI had an accuracy of 78.6% and 75% in unmasking abnormal stress MBF and MFR in ¹⁵O-water and 82.7% and 71.2% in ¹³N-ammonia studies, respectively. Addition of vFAI to anatomical CCTA data increased the ability for predicting abnormal stress MBF and MFR in ¹⁵O-water studies [AUCccta + vfai = 0.866, 95% confidence interval (CI) 0.783–0.949; P = 0.013 and AUCccta + vfai = 0.737, 95% CI 0.648–0.825; P = 0.007, respectively]. An incremental value was also demonstrated for prediction of stress MBF (AUCccta + vfai = 0.887, 95% CI 0.799–0.974; P = 0.001) in ¹³N-ammonia studies. A similar trend was recorded for MFR (AUCccta + vfai = 0.780, 95% CI 0.632–0.929; P = 0.13). Conclusion vFAI identifies accurately the presence of impaired vasodilating capability. In combination with anatomical data, vFAI enhances the diagnostic performance of CCTA.