Are Instantaneous Wave-Free Ratio Measurements Influenced by Vessel Position?

Background: Instantaneous wave-free ratio (iFR) is used to guide decision-making in percutaneous coronary intervention (PCI), with a ratio of ≤0.89 widely used as indication of haemodynamic significance. An observation of higher iFR values in the left circumflex (LCx) and right coronary artery (RCA) as compared with the left anterior descending (LAD), including ratios >1.0, has previously been reported. This study reported iFR values and vessel location in 226 patients (324 lesions). Method: A total of 226 patients had 323 lesions assessed by iFR. Lesion location was: six LMCA (2%), 188 LAD (58%), 63 LCx (20%), and 66 RCA (20%). Results: Of six LM lesions, one had iFR ≤0.89 and none ≥1.0. In the LAD, mean iFR (SD) was 0.88 (0.1); 83 (44%) had iFR ≤0.89 and one (0.5%) ≥1.0. In the LCx, mean iFR (SD) was 0.91 (0.17); 14 (22%) had iFR ≤0.89 and 27 (43%) ≥1.0. In the RCA, mean iFR (SD) was 0.94 (0.14); seven (10%) had iFR ≤0.89 and 21 (32%) ≥1.0. Of all lesions with iFR ≥1.0, 55% were in LCx, 43% were in RCA, and 2% in LAD. Conclusion: The current centre has continued to show a trend to higher iFR values in LCx and RCA, including large proportions of values >1.0 despite no significant drift on pullback. It was hypothesised that this is the result of hydrostatic pressure variations due to the difference in height between the catheter tip (at which the pressure transducer is calibrated) and the posterior coronary arteries. As most iFR measurements are of borderline significance, this could influence the management of intermediate coronary lesions.