Optimizing the Technique for Invasive Fractional Flow Reserve to Assess Lesion-Specific Ischemia

Invasive fractional flow reserve (FFR_INV) is the standard technique for assessing myocardial ischemia. Pressure distortions and measurement location may influence FFR_INV interpretation. We report a technique for performing invasive fractional flow reserve (FFR_INV) by minimizing pressure distortions and identifying the proper location to measure FFR_INV.

FFR_INV recordings were obtained prospectively during manual hyperemic pullback in 100 normal and diseased coronary arteries with single stenosis, using 4 measurements from the terminal vessel, distal-to-the-lesion, proximal vessel, and guiding catheter. FFR_INV profiles were developed by plotting FFR_INV values (y-axis) and site of measurement (x-axis), stratified by stenosis severity. FFR_INV≤0.8 was considered positive for lesion-specific ischemia.

Erroneous FFR_INV values were observed in 10% of vessels because of aortic pressure distortion and in 21% because of distal pressure drift; these were corrected by disengagement of the guiding catheter and re-equalization of distal pressure/aortic pressure, respectively. There were significant declines in FFR_INV from the proximal to the terminal vessel in normal and stenotic coronary arteries (P<0.001). The rate of positive FFR_INV was 41% when measured from the terminal vessel and 20% when measured distal-to-the-lesion (P<0.001); 41.5% of positive terminal measurements were reclassified to negative when measured distal-to-the-lesion. Measuring FFR_INV 20 to 30 mm distal-to-the-lesion (rather than from the terminal vessel) can reduce errors in measurement and optimize the assessment of lesion-specific ischemia.

Meticulous technique (disengagement of the guiding catheter, FFR_INV pullback) is required to avoid erroneous FFR_INV, which occur in 31% of vessels. Even with optimal technique, FFR_INV values are influenced by stenosis severity and the site of pressure measurement. FFR_INV values from the terminal vessel may overestimate lesion-specific ischemia, leading to unnecessary revascularization.