Coronary Physiology to Guide Percutaneous Coronary Intervention: Why, When, and How

Figures

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  Figure 1. Longitudinal vessel interrogation with a nonhyperemic index with dedicated analysis software. Intracoronary pressure pullback curve in diseased coronary vessels show ups and downs caused by the Venturi effect. Intraluminal pressure (Pd) decreases with higher flow velocity within coronary stenoses, causing dips of intracoronary pressure ratio values. Dedicated software for analysis of pullback curves omits such transient dips. This facilitates the interpretation of the pullback curve and the prediction of the effect of PCI on vessel hemodynamics. NHPR, nonhyperemic pressure ratio.

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  Figure 2. Approaches to longitudinal vessel analysis with wire-based physiology tools. (A) iFR pullback curve displays continuous iFR values on a beat-to-beat basis along the length of vessel. By visually inspecting the step-up patterns, it is possible to discriminate focal vs diffuse disease. (B) Calculation of the PPG index using FFR pullback. Values of PPG index reflect focal (closer to 1) or diffuse (closer to 0) patterns of obstructive disease. (C) The instantaneous FFR gradient per unit time (dFFR(t)/dt) quantifies the amount of FFR changes across the target stenosis. The presence of a major FFR gradient (dFFR(t)/dt ≥ 0.035) predicts a good functional PCI result. Conversely, a minor FFR gradient (defined as 0.035 ≥ dFFR(t)/dt ≥ 0.015), reflecting diffuse atherosclerotic disease patterns, is associated with worse functional PCI results. FFR, fractional flow reserve; iFR, instantaneous wave-free ratio; PCI, percutaneous coronary intervention; PPG, pressure pullback gradient. Adapted with permission from Lee et al.28

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  Figure 3. Coregistration of iFR pullback with the coronary angiogram. Losses in iFR value documented over the vessel are displayed over the coronary angiogram as yellow beads, each accounting for a loss in 0.01 iFR units. Accumulation of yellow beads at a specific vessel location denotes a more focal pattern of flow-limiting disease (A), while a more spread out distribution of beads over the vessel is characteristic of a diffuse pattern (B). Frequently, a mixed pattern of focal and diffuse obstructive disease is documented (C). iFR, instantaneous wave-free ratio.

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  Central Illustration. Stepwise approach using invasive physiological PCI guidance. Left panel: The first step of physiology-guided PCI is assessing the overall burden of ischemia caused by the vessel, and this is best achieved by placing the pressure wire as distally as safely possible within the vessel after normalization. The spot use of resting (iFR, resting full-cycle ratio, diastolic pressure ratio, diastolic hyperemia-free ratio) and/or hyperemic indices (FFR) provide a quantifiable metric that should not be interpreted strictly dichotomously, but instead seen as a probability of epicardial ischemia. Resting indices and/or FFR can be used in isolation or together in a Bayesian approach. Middle panel: If epicardial ischemia is unlikely following spot distal measurements (resting indices >0.95 or FFR >0.85), full vessel pullback is not needed and, following drift check, assessment can be ended. In all other cases, with borderline or more significant lesions, a full vessel pullback is essential for better understanding of when and how revascularization should be performed. Resting indices offer an advantage for pullback as they suffer less from cross-talk between lesions. At this stage, “virtual…

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  Figure 4. Stepwise approach using invasive physiologic PCI guidance.Left panel: The first step of physiology-guided PCI is assessing the overall burden of ischemia caused by the vessel, and this is best achieved by, following normalization, placing the pressure wire as distal as safely possible within the vessel. The spot use of resting (iFR, RFR, dPR, DFR) and/or hyperemic (FFR) indices provide a quantifiable metric that should not be interpreted strictly dichotomously but, instead, seen as a probability of epicardial ischemia. Resting indices and/or FFR can be used in isolation or together in a Bayesian approach. (Middle panel) If epicardial ischemia is unlikely following spot distal measurements (resting indices > 0.95 or FFR > 0.85), full-vessel pullback is not needed, and following drift check, assessment can be ended. In all other cases, with borderline or more significant lesions, a full-vessel pullback is essential for better understanding of when and how revascularization should be performed. Resting indices offer an advantage for pullback as they experience less crosstalk between lesions. At this stage, “virtual PCI” can be performed for estimation of physiologic gain following…