Impact of hydrostatic pressure on fractional flow reserve: in vivo experimental study of anatomical height difference of coronary arteries

Background Although pressure equalization of the sensor-tipped guidewire and systemic pressure is mandatory in measuring fractional flow reserve (FFR), pressure in the distal artery (Pd) with wire advancement can be influenced by hydrostatic pressure related to the height difference between the catheter tip and the distal pressure sensor. We therefore analyzed the impact of hydrostatic pressure on FFR in vivo by modification of the height difference. Methods To reveal the anatomical height difference in human coronary arteries, measurement was performed during computed tomography angiography (CTA) of five consecutive patients. Utilizing the healthy coronary arteries of female swine, height difference diversity was reproduced by body rotation and vertical inclination. FFR measurements were performed during maximum hyperemia with adenosine. The height difference was calculated fluoroscopically with a contrast medium–filled balloon for reference. Results In human coronary CTA, height averages from the ostium in the left anterior descending artery (34.6 mm) were significantly higher than in the left circumflex (−15.5 mm, p = 0.008) and right coronary arteries (−2.3 mm, p = 0.008). In our swine model, reproduced height variation ranged from −7.2 cm to +6.5 cm. Mean FFR was significantly lower in positive sensor height and higher in negative sensor height compared to the reference height. Linear regression analyses revealed significant correlations between height difference and FFR, observed among all coronary arteries, as well as between the height difference and Pd–aortic pressure mismatch. Subtracting 0.622 mmHg/cm height difference from Pd could correct the expected hydrostatic pressure influence. Conclusion Hydrostatic pressure variation resulting from sensor height influenced FFR values might affect interpretation during FFR assessment.