Mislabelled table entries in ADVISE Registry by Petraco and colleagues

Abstract

Petraco and colleagues1 have presented the “adjusted” accuracy comparing their new index (instantaneous wave-free ratio, iFR) against the gold standard of fractional flow reserve (FFR). However, Table 2 of their manuscript misrepresents theoretical calculations as clinical observations. Misleading column labels hide the fact from the casual reader that many of its numbers are assumed from a model instead of being measured directly. Specifically, in three of the four studies (ADVISE registry, ADVISE study, FFR-PET study) FFR values were measured only once, yet the table makes no distinction among the agreement data in its “Repeated FFR measurements” column. Even for the DEFER study, which actually repeated FFR measurements, the authors did not have access to the full raw data. Similarly, two of the four studies (DEFER, FFR-PET study) never measured iFR, yet the table presents an “observed” agreement between iFR and FFR for all rows. Should not measured values – true observations – be distinguished from assumptions? For the last row of the table (FFR-PET study), this confluence of hypothetical values reaches too far, calculating an “adjusted” iFR accuracy by dividing the iFR-FFR agreement (for a study that never measured iFR at all) by the repeated FFR agreement (for a study that only measured FFR once). Only after careful reading of the methods section can the reader uncover that five of the eight values (>50%) in the “Overall classification agreement” columns of Table 2 are an estimation instead of a measurement. Indeed, each and every “adjusted” iFR accuracy in Table 2 contains at least one component that has been assumed from a model. Therefore, their statement that the so-called adjusted “iFR accuracy is almost identical, ranging from 94% to 96%” follows trivially from the underlying assumptions. To our knowledge, in the peer-reviewed literature only the VERIFY study2 has actually measured both iFR and FFR twice in the same patients. The VERIFY study found superior reproducibility for repeated FFR measurements compared to repeated iFR measurements. Even their proposal to “adjust” the agreement suffers from three statistical shortcomings as we will detail in a future manuscript. First, mathematically it does not estimate the true, underlying agreement between the two variables. Second, it only accounts for variability in FFR while neglecting the variability in iFR measurements. Third, it does not generalise beyond a single repetition, whereas investigators may perform two or even more repeated measurements. Fundamentally, Table 2 by Petraco and colleagues falls short of presenting its contents accurately.