Introduction and objectives: The reliability of quantitative flow ratio (QFR) has been questioned. Our aim was to evaluate the diagnostic accuracy of QFR in intermediate nonculprit lesions during the index ST-segment elevation myocardial infarction (STEMI) procedure compared with positive pressure wire-based fractional flow reserve (FFR ≤ 0.80) in a staged procedure.

Methods: This was a substudy of the multicenter, controlled, and randomized VULNERABLE trial, including 428 intermediate nonculprit lesions from 388 consecutive STEMI patients undergoing FFR assessment in a staged procedure between 1 and 60 days. Off-line QFR analyses were performed during both the index and staged procedures. The primary objective was to assess the diagnostic accuracy of index QFR compared with staged positive FFR.

Results: Angiographic vessel diameter (2.80 ± 0.59 vs 2.91 ± 0.57 mm; P < .01), stenosis severity (51.33 ± 8.04% vs 50.54 ± 7.63%; P = .053), and QFR values (0.85 ± 0.09 vs 0.86 ± 0.09; P = .120) showed minimal changes between the index and staged procedures. Moderate concordance was observed between index QFR and staged FFR (kappa index = 0.629; intraclass correlation coefficient = 0.641). The diagnostic accuracy of index QFR for predicting positive FFR was good (area under the curve = 0.825). An index QFR cutoff ≤ 0.80 showed moderate sensitivity (72%) and excellent specificity (91%). An index QFR ≤ 0.87 achieved a sensitivity of 86% for detecting lesions with positive FFR, with 55% of lesions presenting QFR ≤ 0.87 at the index procedure.

Conclusions: Index QFR demonstrated good diagnostic accuracy for identifying lesions with positive FFR in a staged procedure. However, an index QFR cutoff value of ≤ 0.80 showed moderate sensitivity and may underdiagnose approximately 3 out of 10 lesions with positive FFR. An index QFR ≤ 0.87 provided higher sensitivity and may help avoid invasive (staged) procedures in many patients..