Impact of Hydrostatic Pressure Variations Caused by Height Differences in Supine and Prone Positions on Fractional Flow Reserve Values in the Coronary Circulation

Abstract

Objectives. To examine the influence of hydrostatic pressure on fractional flow reserve (FFR) in vivo.Background. Systematic differences in FFR values have been observed previously in the left anterior descending artery (LAD), left circumflex artery (LCX), and right coronary artery (RCA). It has been suggested that as the hydrostatic pressure variations caused by the height differences between the catheter tip (mean aortic pressure (Pa)) and pressure-wire sensor (mean distal intracoronary pressure (Pd)) are small, intracoronary pressure need not be corrected.Methods. Resting Pd/Pa and FFR values in 23 patients (27 lesions) were measured and compared in supine and prone positions. These values were corrected by hydrostatic pressure influenced by height levels and compared. Height differences between Pa and Pd were calculated using coronary computed tomography angiographies.Results. In LAD, resting Pd/Pa and FFR values were significantly higher in the prone position than in the supine position (0.97 ± 0.05 vs 0.89 ± 0.04,P<0.001(resting Pd/Pa); 0.81 ± 0.09 vs 0.72 ± 0.07,P<0.001(FFR)). Conversely, in LCX and RCA, these values were significantly lower in the prone position (LCX: 0.93 ± 0.03 vs 0.98 ± 0.03,P<0.001(resting Pd/Pa); 0.84 ± 0.05 vs 0.89 ± 0.04,P<0.001(FFR); RCA: 0.91 ± 0.04 vs 0.98 ± 0.03,P=0.005(resting Pd/Pa); 0.78 ± 0.07 vs 0.84 ± 0.07,P=0.019(FFR)). FFR values corrected by hydrostatic pressure showed good correlations in the supine and prone positions (R2 = 0.948 in LAD;R2 = 0.942 in LCX;R2 = 0.928 in RCA).Conclusions. Hydrostatic pressure variations due to height levels influence intracoronary pressure measurements and largely affect resting Pd/Pa and FFR, which might have caused systematic differences in FFR values between the anterior and posterior coronary territories.

The impact of hydrostatic pressure on the result of physiological measurements in various coronary segments

“…Given the dichotomous interpretation of stenosis severity by the FFR measurement, we found a similar rate in the change of classification of an intermediate severity coronary artery stenosis after adjusting for hydrostatic pressure as in previous publications [ 15 – 18 ]. As a result of the correction of pressure ratios at 100 Hgmm aortic pressure, the interpretation of the measurements changed in 5 (12%) and 11 (27%) cases in our study population.…”

“…According to Pascal´s law the hydrostatic pressure in the coronary arteries can be assumed as 0.77 mmHg per cm height difference, in case of a normal mass density (1050 kg/m 3 ). Studies applying CT coronary angiography have previously showed that pressure differences are systematically detectable between the anterior and posterior coronary territories in supine position [ 15 – 18 ]. Moreover, height measurements at the highest or lowest points of the individual vessels indicated remarkable differences.…”

“…Moreover, height measurements at the highest or lowest points of the individual vessels indicated remarkable differences. In a previous study, intracoronary pressure measurements (resting Pd/Pa and FFR) were carried out in both supine and prone positions, and height differences were analyzed based on CT images [ 15 ]. These studies unequivocally found a significantly lower resting Pd/Pa and FFR values measured in the LAD, while higher values were demonstrated when measurements were carried out in the CX or RCA [ 15 – 18 ].…”

“…In recent years, studies investigating the effect of hydrostatic pressure on intracoronary indices have been published. Most of these examinations were performed using computed tomography (CT) angiographies to calculate the height differences between the orifice and the different segments of the coronary arteries [ 15 – 18 ]. Recently, an invasive angiography-based study has also highlighted the importance of height difference during pressure measurements at the highest and lowest sensor positions, potentially influencing FFR, iFR and Pd/Pa values.…”

Association between plasma xanthine oxidoreductase activity and in-hospital outcomes in patients with stable coronary artery disease after percutaneous coronary intervention

“…The indications for PCI in this study were as follows: 1) Patients in whom the perfusion zone of the coronary artery with significant stenosis (American Heart Association classification >75%) coincided with the area of ischemia demonstrated by noninvasive ischemia evaluation test or 2) Patients with moderate stenosis (50–75% stenosis) or multi-vessel lesions demonstrated by CAG and ischemia by fractional flow reserve (FFR), but with a vessel diameter that allows drug-eluting stent implantation. FFR evaluation was performed following procedures previously described [ 10 ]. The exclusion criteria of PCI included acute coronary syndrome, receiving hemodialysis or PCI failure.…”