Routine Pressure-Derived Fractional Flow Reserve Guidance: From Diagnostic to Everyday Practice

Coronary angiography remains the most widely used means of assessing the severity of coronary stenosis. Despite its universal acceptance, coronary angiography is simply luminography, and is inherently limited in determining the physiological significance of coronary stenoses.1,2 During recent years, the pressure-derived myocardial fractional flow reserve (FFR) index, once used only as a research tool, has gained wide acceptance for determining the physiological significance of a coronary stenosis. FFR is defined as the ratio of the maximal blood flow achievable in a stenotic vessel to the normal maximal flow in the same vessel, which represents the fraction of maximum flow that can still be maintained despite the presence of the stenosis. The development of a pressure sensor-tipped angioplasty guidewire,3 which permits measurement of coronary pressure distal to coronary obstructions, has proven clinically practical and has been accepted as a valuable adjunct to coronary angiography in the catheterization laboratory. FFR is a lesion-specific index of the functional severity of coronary stenosis and has a clearly-defined cutoff value that correlates well with the findings from a variety of noninvasive stress tests.4 In patients with intermediate coronary lesions, a FFR value 0.90 and a residual diameter stenosis of 0.90, the restenosis rates at 6, 12 and 24 months were 11%, 12% and 15% compared with 29%, 32% and 42% in patients with post-BA FFR 0.95, the event rate was 4.9%; for values between 0.90 and 0.95, it was 6.2%; for values between 0.80 and 0.90, it was 20.3%; and for post-stenting FFR 0.94 corresponded very well with IVUS results. On the other hand, a recent study conducted by Fearon et al.32 comparing stent implantation guidance with FFR showed that a post-stenting FFR 0.96 did not reliably predict an optimal result based on validated IVUS criteria. Although the question of whether post-stenting FFR is reliable in guiding optimal stent implantation is still a controversial issue, it is generally accepted that the higher the post-stenting FFR value, the lower the event rate and the better the long-term outcome. C. FFR and Intravascular Ultrasound In order to understand whether IVUS has clinical potential to assess the functional severity of coronary stenosis, Takagi and colleagues33 evaluated the relationship between IVUS parameters and the FFR index in 41 patients. Their results showed that the combination of both minimal lumen area of 60% by IVUS reliably predicted a FFR below 0.75, with a sensitivity of 92% and a specificity of 89%. Briguori et al.34 also compared IVUS with FFR in patients with intermediate coronary stenosis. They found that a minimal lumen diameter of 70%, a minimal lumen cross-sectional area of 10 mm were the best cutoff values for FFR 0.75. However, only 50% of lesions with an area of stenosis > 70% had FFR values

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