A New (Virtual) Reality: Treatment Planning with CT-Derived Fractional Flow Reserve

JACC in a Flash | Can taking a virtual view of a lesion through computed tomographic angiography (CTA) improve treatment and predict functional outcome after stenting? CTA-derived fractional flow reserve (FFR) is a novel noninvasive technology that, according to the authors of a recent study in JACC Cardiovascular Interventions, has the potential to identify ischemia-causing stenosis that would best be treated by medical therapy and/or invasive strategy.

Figure Graphic
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FIGURE: (A) Post-stenting FFR was 0.74, as the ostial lesion (red arrowhead) of LAD was not covered. Intravascular ultrasound showed the uncovered plaque at the ostium of LAD (upper right). FFRct without covering the LAD ostial lesion was 0.76, but it was 0.81 after treating the whole LAD lesion. (B) Post-stent FFR in the left circumflex (LCX) artery was 0.88 despite an angiographically significant stenosis at the ostium of LCX. As part of pre-procedural planning prior to an invasive procedure, functional significance of the ostial lesion could be assessed via FFRct after virtual stenting of distal LCX lesion (post-virtual stenting FFRct 0.83).

To test the validity of the pretreatment model, Kyung-Hee Kim, MD, and colleagues from Seoul National University Hospital in Korea, compared the accuracy of CT-derived FFR (FFRct) with conventional FFR before and after stenting in 44 stable patients (with a total of 48 lesions) from three centers. FFRct was computed in blinded fashion, using CTA and computational fluid dynamics before and after virtual coronary stenting. To perform virtual stenting, the researchers modified the 3-D computation model generated from FFRct to restore the area of the target lesion according to the proximal and distal reference areas.

Prior to intervention, invasive FFR was 0.70±0.14, and this increased to 0.90±0.05 after stenting. Noninvasive FFRct prior to intervention was 0.70±0.15, and this increased to 0.88±0.05 after virtual coronary stenting. Kim et al. found a positive correlation between FFR and FFRct both before and after intervention (p < 0.001), and the mean disagreement between CT-derived and conventional FFR was low 0.006 for pre-intervention and 0.024 for post-intervention.

Overall, the diagnostic accuracy of this novel noninvasive method, in terms of predicting or ruling out myocardial ischemia, was 96% (positive predictive value 50%, negative predictive value 100%) after stenting, as defined by a post-stent FFR of > 0.80. (Sample cases illustrating the potential of virtual stenting to guide treatment planning can be seen in the FIGURE.)

"It is important to note that virtual stenting is performed by modification of the computational model derived from the original [coronary CTA] taken before the invasive procedure, and that post-stent FFR can be predicted from this same model without any additional noninvasive or invasive procedures," Dr. Kim and colleagues wrote. While more data from larger cohorts are needed, they also suggest that clinical application of such a noninvasive planning approach has the potential to reduce clinically unnecessary interventions, procedural time, radiation dose, and costs.

Kim K-H, Doh J-H, Koo B-K, et al. JACC Cardiovasc Interv. 2013 December 11. [Epub ahead of print]

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