Original title: FIRST: Fractional Flow Reserve and Intravascular Ultrasound Relationship Study Reference: Ron Waksman et al. J Am Coll Cardiol 2013. Article in Press

For patients with angiographically assessed intermediate lesions such as stenosis between 40% and 80%, criteria that favor revascularization remains under debate. 

Fractional Flow Reserve (FFR) is considered the gold standard to assess intermediate lesions, and ≤ 0.8 is considered a significative value. Intravascular ultrasound has traditionally used a 4 mm2 cut-off minimum lumen area (MLA) to classify a lesion as severe; however, this cut-off IVUS value has not been proved equivalent to the functional parameter of FFR.

This prospective, multicenter registry designed to determine the correlation between FFR, IVUS and virtual histology (VH) in intermediate lesions included 350 patients (367 intermediate lesions). Whether to perform an angioplasty procedure or not was the operator’s decision.

ROC analysis identified the 3.07 mm2 global MLA cut-off by IVUS as the best threshold to indentify <0.8 FFR lesions (64% sensitivity, 64% specificity). This global MLA cut-off changes according to the vessel’s reference diameter. For vessels < 3.0 mm in diameter, MLA is <2.4 mm2, vessels between 3.0 and 3.5 mm, MLA = <2.7 mm2 and vessels >3.5 mm, MLA = <3.6 mm2. With these optimal MLA cut-offs by IVUS, taking FFR as gold standard, false positives reached 25.7%. A plaque burden of 68.7 ± 11.2% was the only HV variable which correlated with a <0.8 FFR.

Conclusion 

Anatomical measurement by intravascular ultrasound has a moderate correlation with FFR and depends on the reference diameter.

Comment 

The therapeutic decision for an intermediate lesion should be taken, firstly, following clinical criteria, since both techniques present limitations. IVUS may be a better tool to guide the strategy and monitor the final outcome of an angioplasty procedure, rather than to decide whether to perform it or not.

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