QAngio XA 3D QFR and CAAS vFFR imaging software for assessing coronary stenosis during invasive coronary angiography

The CAAS vFFR software (Pie Medical Imaging) works by building a 3D reconstruction of a coronary artery as well as assessing the pressure drop across the stenosis and calculating a vFFR value. Therefore, it gives both anatomical and functional assessments of the stenosis. It uses 2 standard X-ray angiograms, and is compatible with most X-ray systems (that is, it is vendor independent). The company claims that the total analysis time is about 2 minutes per coronary artery. Thresholds for interpretation of vFFR are not provided in the instructions for use document.

The QAngio software (Medis Medical Imaging) uses X-ray angiographic images taken during invasive coronary angiography. Two images are needed, which have to be taken with at least 25 degrees difference in viewing angle and with a frame speed of at least 12.5 frames per second. High image quality is crucial for appropriate results. The QAngio software creates a 3D anatomical model of a coronary artery from these 2 images, and then estimates QFR from the 3D vessel anatomy and flow velocity. The company claims that the total analysis time is about 4 to 5 minutes per coronary artery. The analysis time may decrease with routine use of the software. The QFR represents an assessment of the pressure drop over the artery, with a value of 1 representing a normally functioning artery with no pressure drop. A 20% or more drop in blood pressure (QFR value of 0.80 or less) is usually considered a significant obstruction, where revascularisation should be considered.

The QAngio software offers 2 different flow models to calculate QFR:

• fixed-flow QFR (fQFR), using fixed-flow velocity and

• contrast QFR (cQFR), using contrast frame count in an angiogram without hyperaemia.
  
  Fixed-flow QFR is faster to compute, but may be less accurate than contrast QFR.