The effect of hydrostatic pressure on invasive measures of coronary physiology

Introduction: Coronary arteries are at differing vertical heights in a supine patient relative to the aortic root. Pressure within an artery varies based on distance from the aorta due to hydrostatic effect. This could impact pressure-based indices of stenosis severity, as the vertical distance between distal and proximal pressure sensors creates a baseline pressure difference. This is neglected in clinical practice, as distal and proximal sensors are considered at the same vertical level. Methods: Pd/Pa, instantaneous wave free ratio (iFR), fractional flow reserve FFR and doppler flow velocity were recorded in 23 coronary stenoses in the standard supine patient position, and in the prone position. Measurements between positions were compared using a Student’s t test for matched pairs. Results: There were significant differences in mean Pd/Pa (0.05), iFR (0.06) and FFR (0.06) when comparing prone and supine positioning (p