The effect of hydrostatic pressure on invasive coronary pressure measurements: Comparison with [15O]H2O-positron emission tomography flow data

Background: Fractional flow reserve (FFR) has emerged as the invasive gold standard for assessing vessel-specific ischemia. However, FFR measurements are influenced by the hydrostatic effect, which might adversely impact the assessment of ischemia. Aims: This study aimed to investigate the impact of hydrostatic pressure on FFR measurements by correcting for the height and comparing FFR with [15O]H2O positron emission tomography (PET)-derived relative flow reserve (RFR). Methods: The 206 patients were included in this analysis. Patients underwent coronary computed tomography angiography (CCTA), [15O]H2O PET, and invasive coronary angiography with routine FFR in every epicardial artery. Height differences between the aortic guiding catheter and distal pressure sensor were quantified on CCTA images. An FFR ≤ 0.80 was considered significant. Results: The study found a reclassification in 7% of the coronary arteries. Notably, 11% of left anterior descending (LAD) arteries were reclassified from hemodynamically significant to nonsignificant. Conversely, 6% of left circumflex (Cx) arteries were reclassified from nonsignificant to significant. After correcting for the hydrostatic pressure effect, the correlation between FFR and PET-derived RFR increased significantly from r = 0.720 to r = 0.786 (p = 0.009). The average magnitude of correction was +0.05 FFR units in the LAD, −0.03 in the Cx, and −0.02 in the right coronary artery. Conclusion: Hydrostatic pressure has a small but clinically relevant influence on FFR measurements obtained with a pressure wire. Correcting for this hydrostatic error significantly enhances the correlation between FFR and PET-derived RFR.