RELATionship bEtween Lesion-level Invasive Fractional Flow Reserve AND Endothelial Wall Shear Stress the RELATE FFR and WSS Study

BACKGROUND AND RATIONALE Despite great advances in atherothrombosis science, the complex interplay of factors leading to plaque progression remains elusive. Specifically, the dynamics leading a stable plaque towards rupture and over imposed thrombosis are largely speculative. Wall shear stress (WSS), the mechanical force elicited by blood flow on the vessel walls, is emerging as a potent trigger of bio-humoral processes eventually leading to endothelial damage, plaque progression and destabilization.

Fractional flow reserve (FFR), assessing the aggregate hemodynamical significance of a stenosis on the subtended myocardium, stratifies the risk of major adverse cardiovascular events and reduces their occurrence when used to guide revascularization. While this event reduction is mainly driven by ischemia-caused urgent revascularization, it is emerging that FFR-guided revascularization may also reduce myocardial infarction.

While the physiological relationship between a lesion's FFR and resulting ischemia in the subtended myocardium is intuitive, the mechanisms linking FFR to atherothrombosis are less clearly defined.

Lesions with lower FFR are associated with adverse atherosclerotic plaque characteristics (APCs), however, the causative nexus of this relationship is not well established. It has been proposed both that the physiological base for this relation underlies in disturbed lesion hemodynamics, occurring at a greater extent as the degree of functional obstruction increases (i.e. FFR reduction drives APCs), and that APCs directly impair the vessel's vasodilatory reserve resulting in detrimental hyperemic perfusion (i.e. APCs drive FFR reduction).

WSS measures the regional tangential hemodynamic forces produced by viscous blood flow on the endothelium, which is established drivers of plaque progression and transformation toward an adverse plaque phenotype. Intriguingly, WSS may thus represent the missing link between FFR and atherothrombosis.