The Impact of Hydrostatic Pressure on Fractional Flow Reserve in Saphenous Vein Grafts

The relationship between height differences related to graft anatomy and physiological pressure indices in coronary bypass grafts has not been studied. We sought to study the impact of hydrostatic pressure on fractional flow reserve (FFR) in saphenous vein grafts (SVGs).

Included were 66 symptomatic patients (76 SVGs) with prior coronary artery bypass grafting who underwent coronary computed tomography angiography (CCTA) preceding invasive coronary angiography with FFR interrogation of ≥ 1 SVGs. The graft course and height excursion were reconstructed based on CCTA images. The impact of hydrostatic pressure on FFR (corrected FFR) was calculated by adding or subtracting 0.077 mmHg to the distal coronary pressure for every millimeter height difference in a supine position between the SVG ostium and the pressure wire tip position.

The height difference (mm) between the SVG ostium and pressure wire tip position was largest for single SVGs to the circumflex artery (Cx; -55.1 ± 17.0), followed by sequential SVGs to the Cx (-51.8 ± 17.3) and the right coronary artery (RCA; -36.7 ± 21.6). The correlation between height difference and uncorrected FFR was -0.59 (p < 0.001). Corrected FFR was lower as compared to uncorrected FFR in the overall cohort (0.86 ± 0.17 vs. 0.88 ± 0.18), in single SVGs to Cx (0.85 ± 0.17 vs. 0.90 ± 0.18), and in sequential SVGs to Cx (0.92 ± 0.14 vs. 0.96 ± 0.15) and RCA (0.82 ± 0.17 vs. 0.85 ± 0.21) (p < 0.001 for all).

Hydrostatic pressure related to height differences along the course anatomy of SVGs can impact FFR measurements, with corrected FFR being significantly lower in SVGs to the Cx and sequential SVGs to the RCA.