FIRST (Fractional Flow Reserve and Intravascular Ultrasound Relationship Study) is multicenter registry report with intermediate coronary lesions, defined as 40% to 80% stenosis by angiography. Totally 350 patients with 367 lesion were enrolled.
FFR is considered gold standard for assessing ischemia of intermediate lesion, FFR of less than 0.8 is considered indication for stenting a lesion. Traditionally cutoff value by IVUS to stent an intermediate lesion was minimal luminal area (MLA) of less than 4.0 mm2 but this was too generous approach so it is criticized. FIRST trial looked into coralataion of IVUS MLA with FFR weather same value of 4.0mm2 to be used for all vessels or does it very with reference vessel diameter (RVD) does “same size fit all”
FIRST trail showed poor correlation of IVUS MLA with FFR and also same size does not fit all vessels and also FFR was not helpful in assessing plaque morphology.
Results of FIRST correlating with FFR of less than 0.8 were
1. Overall MLA of less than 3.07 mm2, 64.0% sensitivity, 64.9% specificity
2. Accuracy improved with reference vessel correlation with MLA
a. MLA less than 2.4 mm2 was best for reference vessel diameters less than 3.0 mm
b. MLA less than 2.7 mm2 was best for reference vessel diameters of 3.0 to 3.5 mm
c. MLA less than 3.6 mm2 was best for reference vessel diameters more than 3.5 mm
3. FFR correlated with plaque burden but not with other plaque morphology.
As there is poor correlation between FFR and IVUS MLA it appears IVUS MLA may not be good choice to decide to stent or to defer stenting of intermediate lesion
Anatomically feasibility can be used by IVUS to guide PCI of intermediate lesions