Measuring fractional flow reserve (FFR) with a 0.014 pressure wire is the standard to assess the functional significance of epicardial coronary artery stenosis. The use of FFR in the clinical practice lags despite strong supporting evidence. Some of the reasons behind this are technical aspects, like pressure wire handling limitations when assessing certain lesions, or how frustrating it can be to lose position and to have to recalibrate pressures when there is too much drift and we are no longer sure the value we have obtained is the real one.
An optical pressure monitoring microcatheter has recently been developed, which can be advanced over a traditional 0.014 guidewire (the one we prefer, the one we use in most cases) and allows us to pull back without losing lesion position. The potential disadvantage of this system might be that it has a higher profile than the pressure wire alone, and this might exaggerate stenosis values, overestimating FFR measurement.
Primary end point was the difference between both measurements, assuming as gold standard the pressure wire value.
The mean difference between the microcatheter and the pressure wire measurements was 0.022 (CI 95%, −0.029 to −0.015). On multivariable analyzis, reference vessel diameter (p=0.027) and lesion length (p=0.044) were independent predictors of bias between the 2 measurements.
FFR measurement with Navvus microcatheter, especially designed to this end, tends to render lower values than pressure wire derived FFR, but the diagnostic and therapeutic impact of this difference seems minimal in most cases.
From the physiological point of view, adding a microcatheter will most likely have a higher impact in lesion flow than pressure wire alone, leading to a higher gradient and, ultimately, a lower FFR, especially in longer lesions and thinner vessels.
The more severe the measurement, the bigger the difference observed vs. the pressure wire, though in most cases, both values resulted functionally significant, so the clinical impact that could change diagnosis and therapy was not modified.
A second generation of microcatheters with a much lower profile is already available, though it has not been tested in this study. On the other hand, FFR guidewires have also evolved, with better torque and handling. At some point, one of these wires will cross the finish line and, most likely, it will be the easiest to handle.
Original title: ACIST-FFR Study (Assessment of Catheter-Based Interrogation and Standard Techniques for Fractional Flow Reserve Measurement).
Reference: William F. Fearon et al. Circ Cardiovasc Interv. 2017 Dec;10 (12).
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