Selecting the Right Fractional Flow Reserve in an Unsteady State: Keep It Simple.

F ractional flow reserve (FFR) works. After 20 years and 3 landmark clinical trials, FFR is arguably the best standard for determining the significance of coronary artery disease. By revealing a specific coronary stenosis’s ischemic potential, FFR often changes clinical decisions on the need for or method of revascularization, leading to demonstrably better clinical outcomes and costeffectiveness. Critical to ensuring continued implementation of any test is the operators’ confidence in an accurate, reliable, and repeatable measurement. The original “instructions for use” from Dr. Pijls stated that FFR should be the distal coronary/arterial pressure ratio (Pd/Pa) during steady-state maximal hyperemia, because “a direct relation between coronary pressure and flow . may be presumed only if coronary resistances are constant (and minimal)” (1). Using this succinct definition, selecting the FFR should be simple. Operators watch the pressures during adenosine infusion, track the Pd/Pa ratios, wait for stable signals, and select the lowest FFR value. However, sometimes the operators must resolve 2 conflicts before finalizing their FFR decision. The first issue is that the manually identified FFR may not always match the automated FFR software, which merely selects the simple minimum Pd/Pa