Pullback Pressure Gradient (PPG) Global Registry: Prospective Evaluation of the Impact of the PPG Index on Clinical Decision Making and Outcomes

A Fractional Flow Reserve (FFR) evaluation comprises measurement of a distal single value and a pullback maneuver during hyperemic conditions. The PPGindex is a novel metric derived from the FFR pullback curve.3 This metric complements the distal FFR value by informing the spatial distribution of epicardial resistance (i.e. focal or diffuse) along the coronary vessel. The PPGindex relies on two components: first, the magnitude of pressure drop determined as a maximal pressure gradient over 20 millimeters relative to the total vessel gradient; and second, the length of functional disease relative to total vessel length. These two parameters are weighted equally to provide a metric that ranges from 0 to 1. PPGindex values approaching 1 represent functional focal coronary artery disease (CAD) whereas values close to 0 represent diffuse functional CAD. Until now, the interpretation of the FFR pullback relied on visual assessment. The PPGindex quantifies the pattern of functional CAD and has been shown to predict functionally complete revascularization. Percutaneous revascularization in vessels with high PPGindex is associated with high post-PCI FFR and vast improvement in epicardial conductance whilst PCI in vessels with low PPGindex results in low post-PCI FFR. An curvilinear relationship is observed between PPGindex and functional gain (i.e. FFR post-PCI minus FFR pre-PCI). The PPGindex, therefore, aims to predict the response to PCI in physiological terms.

Calculation of the PPGindex is indicated in cases with an FFR≤0.80. FFR pullbacks are performed under hyperemic conditions at a steady pace during manual pullback. A calculation of the PPGindex using the Coroflow console (Coroventis Research Ab, Uppsala, Sweden) is available for online use and computes the PPG value immediately after the pullback maneuver. This software also includes an automated drift correction. The pullback curve is depicted on an dedicated pullback display screen and the pressure gradients are shown per millimeter, allowing correlation between the location of pressure step-ups and the anatomical target for PCI. In summary, we can distinguish three points where FFR influences the clinical decision-making process. First, an FFR ≤0.80 indicates potential benefit of revascularization. Second, the pullback curve assesses disease pattern and PPG index value quantifies it, helping de physician in the decision about treatment options (e.g. PCI, CABG or OMT). And, third, the location of pressure step-ups along the vessels helps plan the PCI strategy with respect to coverage of functional disease. A combined FFR and PPG-guided PCI strategy has the potential to improve patient selection and enhance procedural planning.

The purpose of this study is to determine the predictive capacity of the PPG index for post-PCI FFR and to determine the impact of the PPG index on clinical decision making about revascularization and on clinical outcomes.