Non-Invasive FFR: CT Evolves from Anatomical to Functional

In the US, more than 4 million patients with chronic stable angina are looking to rule out heart disease. Most undergo functional diagnostic studies that might lead to invasive coronary angiography followed by revascularization. CT has become an alternative diagnostic tool thanks to its precision to rule out heart disease (negative predictive value between 97 and 99%) but has little positive predictive value (64% to 86%).

To improve positive predictive value, new programs using fluid dynamics models have been developed to calculate non-invasive FFR derived from CT (FFRCT).

Read also: “Routine FFR in Patients with Acute Coronary Syndrome?”

FFRCT has relatively good correlation with (r=0.82) invasive FFR, showing 86% sensitivity and 79% specificity.

The PROMISE study (PROspective Multicenter Imaging Study for Evaluation of Chest Pain) which tested the efficacy of CT coronary angiography, offered the chance to exploit the potential of FFRCT in addition to anatomical information.

The observational study determined the correlation between positive FFRCT (≤0.80) and both conventional invasive and CT angiography. Left main lesions ≥50% and ≥70% lesions in other coronary arteries were considered significant. In addition to correlation with conventional studies, researchers assessed FFRCT predictive capacity of death, infarction or unstable angina.

Read also: “SYNTAX II: Better Stents, IVUS, FFR, or a Combination of All of Them to Catch Up with Surgery”.

FFRCT was discordant with 31% of lesions assessed by CT and with 29% of those assessed by conventional angiography. The vast majority of patients that finally underwent revascularization (91%) had ≤0.80 FFRCT.

≤0.80 FFRCT was a significantly lower predictor of revascularization or events than CT angiography. (HR: 4.3 vs HR: 2.9; p=0.033).

Reserving invasive coronary angiography only for those with ≤0.80 FFRCT could save 44% of patients the trouble of an invasive procedure and, in turn, increase the number of invasive coronary angiography procedures followed by revascularization in 24%.

Read also: “COMPARE-ACUTE: FFR-Guided Non-Culprit Vessel Revascularization in Primary Angioplasty”.

This study should be considered only as a hypothesis generator. However, its outcomes are no less interesting.

Conclusion

CT fractional flow reserve (FFRCT) resulted a tool with better predictive value of events and revascularization than anatomical stenosis alone. Adding FFRCT could improve the efficacy of CT to refer patients to new invasive studies.

Original title: Noninvasive FFR Derived from Coronary CT Angiography. Management and Outcomes in the PROMISE Trial.

Reference: Michael T. Lu et al. J Am Coll Cardiol Img 2017. Article in press.

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