Impact of vascular morphology and plaque characteristics on computed tomography derived fractional flow reserve in early stage coronary artery disease.

Background: Computed-tomography (CT) derived fractional-flow-reserve (FFR) gradually may decrease from proximal to distal vessels even without apparent coronary artery disease (CAD). It may be unclear whether the decrease in FFR at the distal coronal artery is physiological or due to stenosis. We decided to study predictive factors of an FFR decline below the pathological value of 0.80 in no-apparent CAD.

Methods: A total of 150 consecutive patients who had both CT angiography coupled to FFR analysis and invasive angiogram showing < 20% coronary stenosis were included. Vessels were divided into two groups according to FFR at the distal vessel: FFR > 0.80 (n = 317) and FFR ≤ 0.80 (n = 114). ΔFFR was defined as the change in FFR from proximal to distal vessel. Vessel morphology (vessel length and lumen volume) and plaque characteristics [low-attenuation plaque volume, intermediate-attenuation (IAP) plaque volume, and calcified plaque volume] were evaluated.

Results: FFR decreased from proximal to distal for the three major vessels in both FFR > 0.80 and FFR ≤ 0.80. Compared to FFR > 0.80, IAP volume was significantly higher in all three major vessels in FFR ≤ 0.80. ΔFFR was correlated with vessel length and lumen volume in FFR > 0.80, whereas ΔFFR was correlated with IAP volume in FFR ≤ 0.80. IAP volume above 44.8 mm was the strongest predictor of distal FFR of ≤ 0.80.

Conclusions: The presence of IAP is a major predictor of gradual decrease of FFR below 0.80 in no-apparent CAD vessels. Vessel morphology and plaque characteristics should be considered when interpreting FFR.