Coronary artery height differences and their effect on fractional flow reserve

Abstract

Background: Fractional flow reserve (FFR) uses pressure-based measurements to assess the severity of a coronary stenosis. Distal pressure (Pd) is often at a different vertical height to that of the proximal pressure (Pa). The difference in pressure between Pd and Pa due to hydrostatic pressure, may impact FFR calculation. Methods: One hundred computed tomography coronary angiographies were used to measure height differences between the coronary ostia and points in the coronary tree. Mean heights were used to calculate the hydrostatic pressure effect in each artery, using a correction factor of 0.8 2 mmHg/cm. This was tested in a simulation of intermediate coronary stenosis to give the "corrected FFR" (cFFR) and percentage of values, which crossed a threshold of 0.8. Results: The mean height from coronary ostium to distal left anterior descending (LAD) was +5.26 cm, distal circumflex (Cx)-3.35 cm, distal right coronary artery-posterior left ventricular artery (RCA-PLV)-5.74 cm and distal RCA-posterior descending artery (PDA) +1.83 cm. For LAD, correction resulted in a mean change in FFR of +0.042,-0.027 in the Cx,-0.046 in the PLV and +0.015 in the PDA. Using 200 random FFR values between 0.75 and 0.85, the resulting cFFR crossed the clinical treatment threshold of 0.8 in 43% of LAD, 27% of Cx, 47% of PLV and 15% of PDA cases. Conclusions: There are significant vertical height differences between the distal artery (Pd) and its point of normalization (Pa). This is likely to have a modest effect on FFR calculation and the results in values crossing the treatment threshold. Operators should be mindful of this phenomenon when interpreting FFR values.

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

“…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][16][17][18]. 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][16][17][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][16][17][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.…”

The Effect of Hydrostatic Pressure on Coronary Flow and Pressure-Based Indices of Coronary Stenosis Severity

“…Such a factor is the effect of the hydrostatic pressure created by the height difference between the distal position of the pressure wire sensor and the coronary ostium where pressure equalization took place. Coronary arteries lie in different vertical planes [ 6 ] and it has been shown that there is significant height variation between the proximal and distal vessels when the patient is lying flat (such as during coronary angiography and invasive physiological measurements) [ 7 , 8 ]. In clinical practice, this hydrostatic pressure effect is ignored, as the actual pressure gradient is usually small (<5 mmHg) [ 9 ].…”

“…In clinical practice, this hydrostatic pressure effect is ignored, as the actual pressure gradient is usually small (<5 mmHg) [ 9 ]. Nevertheless, recent studies have suggested that the hydrostatic pressure gradient influences significantly pressure-based physiological indices [ 7 , 10 , 11 , 12 , 13 , 14 , 15 ], and as such the quantification of the hydrostatic impact on clinical practice remains poorly understood.…”