Delineating the guide-wire flow obstruction effect in assessment of fractional flow reserve and coronary flow reserve measurements

Abstract

Hemodynamic analysis was conducted to determine uncertainty in clinical measurements of coronary flow reserve (CFR) and fractional flow reserve (FFR) over pathophysiological conditions in a patient group with coronary artery disease during angioplasty. The vasodilation-distal perfusion pressure (CFR-p̃rh) curve was obtained for 0.35- and 0.46-mm guide wires. Our hypothesis is that a guide wire spanning the lesions elevates the pressure gradient and reduces the flow during hyperemic measurements. Maximal CFR-p̃rh was uniquely determined by the intersection of measured CFR and calculated p̃rh of native and residual epicardial lesions in patients without microvascular disease, during angioplasty. Extrapolation of the linear curve gave a zero-coronary flow mean pressure (p̃zf) of ∼20 mmHg and a corresponding p̃rh of 55 mmHg in the native lesions, which coincided with the level that causes ischemia in human hearts. On this linear curve, values of CFR and FFRmyo (pathophysiological condition) and CFRg and FFRmyog (in the presence of the guide wire) were obtained in native and residual lesions. A strong linear correlation was found between CFR and CFRg [CFR = CFRg × 0.689 + 1.271 ( R2 = 0.99) for 0.46 mm and CFR = CFRg × 0.757 + 1.004 ( R2 = 0.99) for 0.35 mm] and between FFRmyo and FFRmyog [FFRmyo = FFRmyog × 0.737 + 0.263 ( R2 = 0.99) for 0.46 mm and FFRmyo = FFRmyog × 0.790 + 0.210 ( R2 = 0.99) for 0.35 mm]. This study establishes a strong correlation between CFR and CFRg and between FFRmyo and FFRmyog, which could be used to obtain the true state of occlusion in the coronary artery during angioplasty.