Background An influence of hydrostatic pressure on intracoronary indices of stenosis severity in vitro was recently reported. We sought to analyze the influence of hydrostatic pressure, caused by the height difference between the distal and proximal pressure sensor after guidewire positioning in the interrogated vessel, on intracoronary pressure measurements in vivo.
Methods and results In 30 coronary stenoses, intracoronary pressure measurements were performed in supine, left, and right lateral patient position. Height differences between the distal and proximal pressure sensor were measured by blinded observers. Measurement results of the position with the highest ("high") and lowest height difference ("low") were compared. In group "high", all measured indices were higher: mean difference of fractional flow reserve (FFR) 0.045 (SD 0.033, 95% CI 0.033-0.057, p <0.0001), of instantaneous wave-free ratio (iFR) 0.043 (SD 0.04, 95% CI 0.029-0.057, p <0.0001), and of resting Pd/Pa 0.037 (SD 0.034, 95% CI 0.025-0.049, p <0.0001). Addition of the physically expectable hydrostatic pressure to the distal coronary pressures of the control group abolished the differences: corrected Delta FFR -0.006 (SD 0.027, 95% CI -0.015 to 0.004, p = 0.26), corrected Delta Pd/Pa -0.008 (SD 0.03, 95% CI -0.019 to 0.003, p = 0.18). Adjustment for hydrostatic pressure of FFR values in a standard supine position increased all values in anterior vessels and decreased all values in posterior vessels. The mean changes of FFR due to adjustment were: LAD -0.048 (SD 0.016), CX 0.02 (SD 0.009), RCA 0.02 (SD 0.021). Dichotomous severity classification changed in 12.9% of stenoses.
Conclusions The study demonstrates a relevant influence of hydrostatic pressure on intracoronary indices of stenosis severity in vivo, caused by the height differences between distal and proximal pressure sensor.